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Samei, Ehsan

Overview:

Dr. Ehsan Samei, PhD, DABR, FAAPM, FSPIE is a tenured Professor of Radiology, Medical Physics, Biomedical Engineering, Physics, and Electrical and Computer Engineering at Duke University, where he also serves as the Director of Carl E. Ravin Advanced Imaging Laboratories and the founding Chief of the Clinical Imaging Physics Group. He is certified by the American Board of Radiology, and is a Fellow of the American Association of Physicists in Medicine (AAPM), and the International Society of Optical Engineering (SPIE). He was the founding Director of the Graduate Studies of the Duke Medical Physics Graduate Program, and the co-founder of the Society of Directors of Academic Medical Physics Programs (SDAMPP). He has held senior leadership positions in the AAPM, the SPIE, and SDAMPP. He is a Councilor of the National Council of Radiation Protection and Measurements (NCRP), and a Distinguished Investigator of the Academy of Radiology Research.


Dr. Samei’s interests and expertise include x-ray imaging, theoretical imaging models, simulation methods, and experimental techniques in medical image formation, analysis, assessment, display, and perception. His current research includes methods to develop image quality and dose metrics that are clinically relevant and that can be used to design and utilize advanced imaging techniques towards precise interpretive and quantitative performance. He further has an active interest in bridging the gap between scientific scholarship and clinical practice, in the meaningful realization of translational research and in clinical processes that are informed by scientific evidence. While he works across most diagnostic imaging modalities, his main modalities of interest are CT and Tomosynthesis for breast, lung, and abdominal imaging applications. He has been the recipient of 29 extramural grants from the US government, private foundations, and medical industry, and has 700 scientific publications including 190 referred journal articles.

Positions:

Professor of Radiology

Radiology
School of Medicine

Professor in the Department of Physics

Physics
Trinity College of Arts & Sciences

Professor of Biomedical Engineering

Biomedical Engineering
Pratt School of Engineering

Member of the Duke Cancer Institute

Duke Cancer Institute
School of Medicine

Education:

M.E. 1995

M.E. — University of Michigan at Ann Arbor

Ph.D. 1997

Ph.D. — University of Michigan at Ann Arbor

Grants:

Precision Cardiac CT: Development of a Computational Platform for Optimizing Imaging

Administered By
Radiology
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
March 15, 2017
End Date
February 28, 2021

Training in Medical Imaging

Administered By
Biomedical Engineering
AwardedBy
National Institutes of Health
Role
Mentor
Start Date
July 15, 2003
End Date
August 31, 2019

Simulation Tools for 3D and 4D CT and Dosimetry

Administered By
Radiology
AwardedBy
National Institutes of Health
Role
Co-Principal Investigator
Start Date
March 01, 2007
End Date
December 31, 2018

Imaging Physics Residency Grant

Administered By
Radiology
AwardedBy
American Association of Physicists in Medicine
Role
Principal Investigator
Start Date
December 01, 2014
End Date
November 30, 2018

Reconstruction Software Evaluation

Administered By
Radiology
AwardedBy
Siemens Medical Solutions USA, Inc.
Role
Principal Investigator
Start Date
July 01, 2014
End Date
February 01, 2018

Methodology and Reference Image set for Volumetric Characterization and Compliance

Administered By
Radiology
AwardedBy
Radiological Society of North America
Role
Principal Investigator
Start Date
September 30, 2014
End Date
September 29, 2017

Reference Image Set for Quantitation Conformance of Algorithmic Lesion Characterization

Administered By
Radiology
AwardedBy
Radiological Society of North America
Role
Principal Investigator
Start Date
September 30, 2014
End Date
September 29, 2017

Advancement and Effective Implementation of Dose and Risk Monitoring Systems

Administered By
Radiology
AwardedBy
GE Healthcare
Role
Principal Investigator
Start Date
January 01, 2014
End Date
September 01, 2017

Decreased Variability for Robust Imaging-based Quantification of Tumor Heterogeneity

Administered By
Radiology, Abdominal Imaging
AwardedBy
Radiological Society of North America
Role
Advisor
Start Date
July 01, 2015
End Date
June 30, 2017

IAEA scientific visit and training

Administered By
Radiology
AwardedBy
International Atomic Energy Agency
Role
Principal Investigator
Start Date
October 17, 2016
End Date
October 21, 2016

Duke Clinical Imaging Physics Group Fellowship

Administered By
Radiology
AwardedBy
Bracco Foundation
Role
Principal Investigator
Start Date
September 07, 2015
End Date
September 06, 2016

A Diagnostic Capability Concurrence study of a SSXI Mobile Fluoroscopy System and the OEC 9900 Elite Mobile Fluoroscopy

Administered By
Radiology
AwardedBy
General Electric Corporation
Role
Investigator
Start Date
October 22, 2013
End Date
April 20, 2016

X-Ray Scatter and Phase Imaging for Explosive Detection

Administered By
Electrical and Computer Engineering
AwardedBy
US Department of Homeland Security
Role
Co-Principal Investigator
Start Date
September 23, 2011
End Date
September 25, 2015

3D Digital Breast Phantoms For Multimodality Research

Administered By
Radiology
AwardedBy
National Institutes of Health
Role
Collaborator
Start Date
January 01, 2010
End Date
January 31, 2014

Cross-disciplinary Training in Medical Physics

Administered By
Radiology
AwardedBy
National Institutes of Health
Role
Director
Start Date
July 01, 2007
End Date
June 30, 2013

Information-Theoretic Based CAD in Mammography

Administered By
Radiology
AwardedBy
National Institutes of Health
Role
Scientist
Start Date
July 01, 2003
End Date
June 30, 2011

Tomosynthesis for Improved Breast Cancer Detection

Administered By
Radiology
AwardedBy
National Institutes of Health
Role
Co Investigator
Start Date
June 20, 2006
End Date
April 30, 2011

Bi-Plane Correlation Imaging for Early Detection of Lung Cancer

Administered By
Radiology
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
September 24, 2004
End Date
June 30, 2010

Task-Specific Optimization of Mammographic Systems

Administered By
Radiology
AwardedBy
United States Army Medical Research and Materiel Command
Role
Principal Investigator
Start Date
February 15, 2004
End Date
March 14, 2007

Resolution Requirements for Mammographic Displays

Administered By
Radiology
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
July 01, 2003
End Date
June 30, 2006

Early Detection of Lung Cancer via Bi-plane Correlation Chest Imaging

Administered By
Radiology
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
July 01, 2001
End Date
June 30, 2004
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Awards:

Fellow. International Society for Optics and Photonics.

Type
National
Awarded By
International Society for Optics and Photonics
Date
January 01, 2010

Fellows. American Association of Physicists in Medicine.

Type
National
Awarded By
American Association of Physicists in Medicine
Date
January 01, 2009

Publications:

Image noise and dose performance across a clinical population: patient size adaptation as a metric of CT performance.

Modern CT systems adjust x-ray flux accommodating for patient size to achieve certain image noise values. The effectiveness of this adaptation is an important aspect of CT performance and should ideally be characterized in the context of real patient cases. The objective of this study was to characterize CT performance with a new metric that includes image noise and radiation dose across a clinical patient population.The study included 1526 examinations performed by three CT scanners (one GE Healthcare Discovery CT750HD, one GE Healthcare Lightspeed VCT, and one Siemens SOMATOM definition Flash) used for two routine clinical protocols (abdominopelvic with contrast and chest without contrast). An institutional monitoring system recorded all the data involved in the study. The dose-patient size and noise-patient size dependencies were linearized by considering a first order approximation of analytical models that describe the relationship between ionization dose and patient size, as well as image noise and patient size. A 3D-fit was performed for each protocol and each scanner with a planar function, and the Root Mean Square Error (RMSE) values were estimated as a metric of CT adaptability across the patient population.The data show different scanner dependencies in terms of adaptability: the RMSE values for the three scanners are between 0.0385 HU1/2 and 0.0215 HU1/2 .A theoretical relationship between image noise, CTDIvol and patient size was determined based on real patient data. This relationship may be interpreted as a new metric related to the scanners' adaptability concerning image quality and radiation dose across a patient population. This method could be implemented to investigate the adaptability related to other image quality indexes and radiation dose in a clinical population. This article is protected by copyright. All rights reserved.

Authors
Ria, F; Wilson, JM; Zhang, Y; Samei, E
MLA Citation
Ria, F, Wilson, JM, Zhang, Y, and Samei, E. "Image noise and dose performance across a clinical population: patient size adaptation as a metric of CT performance." Medical physics (February 24, 2017).
Website
http://hdl.handle.net/10161/13805
PMID
28235130
Source
epmc
Published In
Medical physics
Publish Date
2017
DOI
10.1002/mp.12172

Effect of Radiation Dose Reduction and Reconstruction Algorithm on Image Noise, Contrast, Resolution, and Detectability of Subtle Hypoattenuating Liver Lesions at Multidetector CT: Filtered Back Projection versus a Commercial Model-based Iterative Reconstruction Algorithm.

Purpose To determine the effect of radiation dose and iterative reconstruction (IR) on noise, contrast, resolution, and observer-based detectability of subtle hypoattenuating liver lesions and to estimate the dose reduction potential of the IR algorithm in question. Materials and Methods This prospective, single-center, HIPAA-compliant study was approved by the institutional review board. A dual-source computed tomography (CT) system was used to reconstruct CT projection data from 21 patients into six radiation dose levels (12.5%, 25%, 37.5%, 50%, 75%, and 100%) on the basis of two CT acquisitions. A series of virtual liver lesions (five per patient, 105 total, lesion-to-liver prereconstruction contrast of -15 HU, 12-mm diameter) were inserted into the raw CT projection data and images were reconstructed with filtered back projection (FBP) (B31f kernel) and sinogram-affirmed IR (SAFIRE) (I31f-5 kernel). Image noise (pixel standard deviation), lesion contrast (after reconstruction), lesion boundary sharpness (average normalized gradient at lesion boundary), and contrast-to-noise ratio (CNR) were compared. Next, a two-alternative forced choice perception experiment was performed (16 readers [six radiologists, 10 medical physicists]). A linear mixed-effects statistical model was used to compare detection accuracy between FBP and SAFIRE and to estimate the radiation dose reduction potential of SAFIRE. Results Compared with FBP, SAFIRE reduced noise by a mean of 53% ± 5, lesion contrast by 12% ± 4, and lesion sharpness by 13% ± 10 but increased CNR by 89% ± 19. Detection accuracy was 2% higher on average with SAFIRE than with FBP (P = .03), which translated into an estimated radiation dose reduction potential (±95% confidence interval) of 16% ± 13. Conclusion SAFIRE increases detectability at a given radiation dose (approximately 2% increase in detection accuracy) and allows for imaging at reduced radiation dose (16% ± 13), while maintaining low-contrast detectability of subtle hypoattenuating focal liver lesions. This estimated dose reduction is somewhat smaller than that suggested by past studies. © RSNA, 2017 Online supplemental material is available for this article.

Authors
Solomon, J; Marin, D; Roy Choudhury, K; Patel, B; Samei, E
MLA Citation
Solomon, J, Marin, D, Roy Choudhury, K, Patel, B, and Samei, E. "Effect of Radiation Dose Reduction and Reconstruction Algorithm on Image Noise, Contrast, Resolution, and Detectability of Subtle Hypoattenuating Liver Lesions at Multidetector CT: Filtered Back Projection versus a Commercial Model-based Iterative Reconstruction Algorithm." Radiology (February 7, 2017): 161736-.
PMID
28170300
Source
epmc
Published In
Radiology
Publish Date
2017
Start Page
161736
DOI
10.1148/radiol.2017161736

CT breast dose reduction with the use of breast positioning and organ-based tube current modulation.

This study aimed to investigate the breast dose reduction potential of a breast-positioning (BP) technique for thoracic CT examinations with organ-based tube current modulation (OTCM).This study included 13 female anthropomorphic computational phantoms (XCAT, age range: 27-65 y.o., weight range: 52-105.8 kg). Each phantom was modified to simulate three breast sizes in standard supine geometry. The modeled breasts were then morphed to emulate BP that constrained the majority of the breast tissue inside the 120° anterior tube current (mA) reduction zone. The OTCM mA value was modeled using a ray-tracing program, which reduced the mA to 20% in the anterior region with a corresponding increase to the posterior region. The organ doses were estimated by a validated Monte Carlo program for a typical clinical CT system (SOMATOM Definition Flash, Siemens Healthcare). The simulated organ doses and organ doses normalized by CTDIvol were used to compare three CT protocols: attenuation-based tube current modulation (ATCM), OTCM, and OTCM with BP (OTCMBP ).On average, compared to ATCM, OTCM reduced breast dose by 19.3 ± 4.5%, whereas OTCMBP reduced breast dose by 38.6 ± 8.1% (an additional 23.8 ± 9.4%). The dose saving of OTCMBP was more significant for larger breasts (on average 33, 38, and 44% reduction for 0.5, 1, and 2 kg breasts, respectively). Compared to ATCM, OTCMBP also reduced thymus and heart dose by 15.1 ± 7.4% and 15.9 ± 6.2% respectively.In thoracic CT examinations, OTCM with a breast-positioning technique can markedly reduce unnecessary exposure to radiosensitive organs in anterior chest wall, specifically breast tissue. The breast dose reduction is more notable for women with larger breasts.

Authors
Fu, W; Tian, X; Sturgeon, GM; Agasthya, G; Segars, WP; Goodsitt, MM; Kazerooni, EA; Samei, E
MLA Citation
Fu, W, Tian, X, Sturgeon, GM, Agasthya, G, Segars, WP, Goodsitt, MM, Kazerooni, EA, and Samei, E. "CT breast dose reduction with the use of breast positioning and organ-based tube current modulation." Medical physics 44.2 (February 2017): 665-678.
PMID
28032894
Source
epmc
Published In
Medical physics
Volume
44
Issue
2
Publish Date
2017
Start Page
665
End Page
678
DOI
10.1002/mp.12076

Size Specific Optimization of CT Protocols Based on Minimum Detectability.

To develop a comprehensive model of task-based performance of CT across a broad library of CT protocols, so that radiation dose and image quality can be optimized within a large multi-vendor clinical facility.80 adult CT protocols from the Duke University Medical Center were grouped into 23 protocol groups with similar acquisition characteristics. A size-based image quality phantom (Duke Mercury Phantom 2.0) was imaged using these protocol groups for a range of clinically relevant dose levels on two CT manufacturer platforms (Siemens SOMATOM Definition Flash and GE CT750 HD). For each protocol group, phantom size, and dose level, the images were analyzed to extract task-based image quality metrics, the task transfer function (TTF) and the noise power spectrum (NPS). The TTF and NPS were further combined with generalized models of lesion task functions to predict the detectability of the lesions in terms of areas under the receiver operating characteristic curve (Az ). A graphical user interface (GUI) was developed to present Az as a function of lesion size and contrast, dose, patient size, and protocol, as well as to derive the necessary dose to achieve a detection threshold for a targeted lesion.The GUI provided the prediction of Az values modeling detection confidence for a targeted lesion, patient size, and dose. As an example, an abdomen pelvis exam for the GE scanner, with a reference task size/contrast of 5-mm/50-HU, and an Az of 0.9 indicated a dose requirement of 4.0, 8.9, and 16.9 mGy for patient diameters of 25, 30, and 35 cm, respectively. For a constant patient diameter of 30 cm and 50-HU lesion contrast, the minimum detected lesion size at those dose levels were predicted to be 8.4, 5.0, and 3.9 mm, respectively.A CT protocol optimization platform was developed by combining task-based detectability calculations with a GUI that demonstrates the tradeoff between dose and image quality. The platform can be used to improve individual protocol dose efficiency, as well as to improve protocol consistency across various patient sizes and CT scanners. This article is protected by copyright. All rights reserved.

Authors
Zhang, Y; Smitherman, C; Samei, E
MLA Citation
Zhang, Y, Smitherman, C, and Samei, E. "Size Specific Optimization of CT Protocols Based on Minimum Detectability." Medical physics (January 25, 2017).
PMID
28122119
Source
epmc
Published In
Medical physics
Publish Date
2017
DOI
10.1002/mp.12125

Automated, patient-specific estimation of regional imparted energy and dose from tube current modulated computed tomography exams across 13 protocols.

Currently, computed tomography (CT) dosimetry relies on surrogates for dose, such as CT dose index and size-specific dose estimates, rather than dose per se. Organ dose is considered as the gold standard for radiation dosimetry. However, organ dose estimation requires precise knowledge of organ locations. Regional imparted energy and dose can also be used to quantify radiation burden and are beneficial because they do not require knowledge of organ size or location. This work investigated an automated technique to retrospectively estimate the imparted energy from tube current-modulated (TCM) CT exams across 13 protocols. Monte Carlo simulations of various head and body TCM CT examinations across various tube potentials and TCM strengths were performed on 58 adult computational extended cardiac-torso phantoms to develop relationships between scanned mass and imparted energy normalized by dose length product. Results from the Monte Carlo simulations indicate that normalized imparted energy increases with increasing both scanned mass and tube potential, but it is relatively unaffected by the strength of the TCM. The automated algorithm was tested on 40 clinical datasets with a 98% success rate.

Authors
Sanders, J; Tian, X; Segars, WP; Boone, J; Samei, E
MLA Citation
Sanders, J, Tian, X, Segars, WP, Boone, J, and Samei, E. "Automated, patient-specific estimation of regional imparted energy and dose from tube current modulated computed tomography exams across 13 protocols." Journal of medical imaging (Bellingham, Wash.) 4.1 (January 24, 2017): 013503-.
PMID
28149922
Source
epmc
Published In
Journal of medical imaging (Bellingham, Wash.)
Volume
4
Issue
1
Publish Date
2017
Start Page
013503
DOI
10.1117/1.jmi.4.1.013503

The Effect of Contrast Material on Radiation Dose at CT: Part I-Incorporation of Contrast Material Dynamics in Anthropomorphic Phantoms.

Purpose To develop a method to incorporate the propagation of contrast material into computational anthropomorphic phantoms for estimation of organ dose at computed tomography (CT). Materials and Methods A patient-specific physiologically based pharmacokinetic (PBPK) model of the human cardiovascular system was incorporated into 58 extended cardiac-torso (XCAT) patient phantoms. The PBPK model comprised compartmental models of vessels and organs unique to each XCAT model. For typical injection protocols, the dynamics of the contrast material in the body were described according to a series of patient-specific iodine mass-balance differential equations, the solutions to which provided the contrast material concentration time curves for each compartment. Each organ was assigned to a corresponding time-varying iodinated contrast agent to create the contrast material-enhanced five-dimensional XCAT models, in which the fifth dimension represents the dynamics of contrast material. To validate the accuracy of the models, simulated aortic and hepatic contrast-enhancement results throughout the models were compared with previously published clinical data by using the percentage of discrepancy in the mean, time to 90% peak, peak value, and slope of enhancement in a paired t test at the 95% significance level. Results The PBPK model allowed effective prediction of the time-varying concentration curves of various contrast material administrations in each organ for different patient models. The contrast-enhancement results were in agreement with results of previously published clinical data, with mean percentage, time to 90% peak, peak value, and slope of less than 10% (P > .74), 4%, 7%, and 14% for uniphasic and 12% (P > .56), 4%, 12%, and 14% for biphasic injection protocols, respectively. The exception was hepatic enhancement results calculated for a uniphasic injection protocol for which the discrepancy was less than 25%. Conclusion A technique to model the propagation of contrast material in XCAT human models was developed. The models with added contrast material propagation can be applied to simulate contrast-enhanced CT examinations. © RSNA, 2017 Online supplemental material is available for this article.

Authors
Sahbaee, P; Segars, WP; Marin, D; Nelson, RC; Samei, E
MLA Citation
Sahbaee, P, Segars, WP, Marin, D, Nelson, RC, and Samei, E. "The Effect of Contrast Material on Radiation Dose at CT: Part I-Incorporation of Contrast Material Dynamics in Anthropomorphic Phantoms." Radiology (January 13, 2017): 152851-.
PMID
28092496
Source
epmc
Published In
Radiology
Publish Date
2017
Start Page
152851
DOI
10.1148/radiol.2016152851

Hallway Conversations in Physics.

Authors
Mileto, A; Samei, E
MLA Citation
Mileto, A, and Samei, E. "Hallway Conversations in Physics." AJR. American journal of roentgenology 208.1 (January 2017): W24-W27.
PMID
27786544
Source
epmc
Published In
AJR. American journal of roentgenology
Volume
208
Issue
1
Publish Date
2017
Start Page
W24
End Page
W27
DOI
10.2214/ajr.16.16462

Accuracy assessment and characterization of x-ray coded aperture coherent scatter spectral imaging for breast cancer classification.

Although transmission-based x-ray imaging is the most commonly used imaging approach for breast cancer detection, it exhibits false negative rates higher than 15%. To improve cancer detection accuracy, x-ray coherent scatter computed tomography (CSCT) has been explored to potentially detect cancer with greater consistency. However, the 10-min scan duration of CSCT limits its possible clinical applications. The coded aperture coherent scatter spectral imaging (CACSSI) technique has been shown to reduce scan time through enabling single-angle imaging while providing high detection accuracy. Here, we use Monte Carlo simulations to test analytical optimization studies of the CACSSI technique, specifically for detecting cancer in ex vivo breast samples. An anthropomorphic breast tissue phantom was modeled, a CACSSI imaging system was virtually simulated to image the phantom, a diagnostic voxel classification algorithm was applied to all reconstructed voxels in the phantom, and receiver-operator characteristics analysis of the voxel classification was used to evaluate and characterize the imaging system for a range of parameters that have been optimized in a prior analytical study. The results indicate that CACSSI is able to identify the distribution of cancerous and healthy tissues (i.e., fibroglandular, adipose, or a mix of the two) in tissue samples with a cancerous voxel identification area-under-the-curve of 0.94 through a scan lasting less than 10 s per slice. These results show that coded aperture scatter imaging has the potential to provide scatter images that automatically differentiate cancerous and healthy tissue within ex vivo samples. Furthermore, the results indicate potential CACSSI imaging system configurations for implementation in subsequent imaging development studies.

Authors
Lakshmanan, MN; Greenberg, JA; Samei, E; Kapadia, AJ
MLA Citation
Lakshmanan, MN, Greenberg, JA, Samei, E, and Kapadia, AJ. "Accuracy assessment and characterization of x-ray coded aperture coherent scatter spectral imaging for breast cancer classification." Journal of medical imaging (Bellingham, Wash.) 4.1 (January 2017): 013505-.
PMID
28331884
Source
epmc
Published In
Journal of medical imaging (Bellingham, Wash.)
Volume
4
Issue
1
Publish Date
2017
Start Page
013505
DOI
10.1117/1.jmi.4.1.013505

Dual-Source Single-Energy Multidetector CT Used to Obtain Multiple Radiation Exposure Levels within the Same Patient: Phantom Development and Clinical Validation.

Purpose To develop, in a phantom environment, a method to obtain multidetector computed tomographic (CT) data sets at multiple radiation exposure levels within the same patient and to validate its use for potential dose reduction by using different image reconstruction algorithms for the detection of liver metastases. Materials and Methods The American College of Radiology CT accreditation phantom was scanned by using a dual-source multidetector CT platform. By adjusting the radiation output of each tube, data sets at six radiation exposure levels (100%, 75%, 50%, 37.5%, 25%, and 12.5%) were reconstructed from two consecutive dual-source single-energy (DSSE) acquisitions, as well as a conventional single-source acquisition. A prospective, HIPAA-compliant, institutional review board-approved study was performed by using the same DSSE strategy in 19 patients who underwent multidetector CT of the liver for metastatic colorectal cancer. All images were reconstructed by using conventional weighted filtered back projection (FBP) and sinogram-affirmed iterative reconstruction with strength level of 3 (SAFIRE-3). Objective image quality metrics were compared in the phantom experiment by using multiple linear regression analysis. Generalized linear mixed-effects models were used to analyze image quality metrics and diagnostic performance for lesion detection by readers. Results The phantom experiment showed comparable image quality between DSSE and conventional single-source acquisition. In the patient study, the mean size-specific dose estimates for the six radiation exposure levels were 13.0, 9.8, 5.8, 4.4, 3.2, and 1.4 mGy. For each radiation exposure level, readers' perception of image quality and lesion conspicuity was consistently ranked superior with SAFIRE-3 when compared with FBP (P ≤ .05 for all comparisons). Reduction of up to 62.5% in radiation exposure by using SAFIRE-3 yielded similar reader rankings of image quality and lesion conspicuity when compared with routine-dose FBP. Conclusion A method was developed and validated to synthesize multidetector CT data sets at multiple radiation exposure levels within the same patient. This technique may provide a foundation for future clinical trials aimed at estimating potential radiation dose reduction by using iterative reconstructions. © RSNA, 2016 Online supplemental material is available for this article.

Authors
Bellini, D; Ramirez-Giraldo, JC; Bibbey, A; Solomon, J; Hurwitz, LM; Farjat, A; Mileto, A; Samei, E; Marin, D
MLA Citation
Bellini, D, Ramirez-Giraldo, JC, Bibbey, A, Solomon, J, Hurwitz, LM, Farjat, A, Mileto, A, Samei, E, and Marin, D. "Dual-Source Single-Energy Multidetector CT Used to Obtain Multiple Radiation Exposure Levels within the Same Patient: Phantom Development and Clinical Validation." Radiology (December 5, 2016): 161233-.
PMID
27935766
Source
epmc
Published In
Radiology
Publish Date
2016
Start Page
161233
DOI
10.1148/radiol.2016161233

Comparison of low-contrast detectability between two CT reconstruction algorithms using voxel-based 3D printed textured phantoms.

To use novel voxel-based 3D printed textured phantoms in order to compare low-contrast detectability between two reconstruction algorithms, FBP (filtered-backprojection) and SAFIRE (sinogram affirmed iterative reconstruction) and determine what impact background texture (i.e., anatomical noise) has on estimating the dose reduction potential of SAFIRE.Liver volumes were segmented from 23 abdominal CT cases. The volumes were characterized in terms of texture features from gray-level co-occurrence and run-length matrices. Using a 3D clustered lumpy background (CLB) model, a fitting technique based on a genetic optimization algorithm was used to find CLB textures that were reflective of the liver textures, accounting for CT system factors of spatial blurring and noise. With the modeled background texture as a guide, four cylindrical phantoms (Textures A-C and uniform, 165 mm in diameter, and 30 mm height) were designed, each containing 20 low-contrast spherical signals (6 mm diameter at nominal contrast levels of ∼3.2, 5.2, 7.2, 10, and 14 HU with four repeats per signal). The phantoms were voxelized and input into a commercial multimaterial 3D printer (Object Connex 350), with custom software for voxel-based printing (using principles of digital dithering). Images of the textured phantoms and a corresponding uniform phantom were acquired at six radiation dose levels (SOMATOM Flash, Siemens Healthcare) and observer model detection performance (detectability index of a multislice channelized Hotelling observer) was estimated for each condition (5 contrasts × 6 doses × 2 reconstructions × 4 backgrounds = 240 total conditions). A multivariate generalized regression analysis was performed (linear terms, no interactions, random error term, log link function) to assess whether dose, reconstruction algorithm, signal contrast, and background type have statistically significant effects on detectability. Also, fitted curves of detectability (averaged across contrast levels) as a function of dose were constructed for each reconstruction algorithm and background texture. FBP and SAFIRE were compared for each background type to determine the improvement in detectability at a given dose, and the reduced dose at which SAFIRE had equivalent performance compared to FBP at 100% dose.Detectability increased with increasing radiation dose (P = 2.7 × 10-59) and contrast level (P = 2.2 × 10-86) and was higher in the uniform phantom compared to the textured phantoms (P = 6.9 × 10-51). Overall, SAFIRE had higher d' compared to FBP (P = 0.02). The estimated dose reduction potential of SAFIRE was found to be 8%, 10%, 27%, and 8% for Texture-A, Texture-B, Texture-C and uniform phantoms.In all background types, detectability was higher with SAFIRE compared to FBP. However, the relative improvement observed from SAFIRE was highly dependent on the complexity of the background texture. Iterative algorithms such as SAFIRE should be assessed in the most realistic context possible.

Authors
Solomon, J; Ba, A; Bochud, F; Samei, E
MLA Citation
Solomon, J, Ba, A, Bochud, F, and Samei, E. "Comparison of low-contrast detectability between two CT reconstruction algorithms using voxel-based 3D printed textured phantoms." Medical physics 43.12 (December 2016): 6497-.
PMID
27908164
Source
epmc
Published In
Medical physics
Volume
43
Issue
12
Publish Date
2016
Start Page
6497
DOI
10.1118/1.4967478

Estimation of Radiation Dose in CT Based on Projection Data.

Managing and optimizing radiation dose has become a core problem for the CT community. As a fundamental step for dose optimization, accurate and computationally efficient dose estimates are crucial. The purpose of this study was to devise a computationally efficient projection-based dose metric. The absorbed energy and object mass were individually modeled using the projection data. The absorbed energy was estimated using the difference between intensity of the primary photon and the exit photon. The mass was estimated using the volume under the attenuation profile. The feasibility of the approach was evaluated across phantoms with a broad size range, various kVp settings, and two bowtie filters, using a simulation tool, the Computer Assisted Tomography SIMulator (CATSIM) software. The accuracy of projection-based dose estimation was validated against Monte Carlo (MC) simulations. The relationship between projection-based dose metric and MC dose estimate was evaluated using regression models. The projection-based dose metric showed a strong correlation with Monte Carlo dose estimates (R (2) > 0.94). The prediction errors for the projection-based dose metric were all below 15 %. This study demonstrated the feasibility of computationally efficient dose estimation requiring only the projection data.

Authors
Tian, X; Yin, Z; De Man, B; Samei, E
MLA Citation
Tian, X, Yin, Z, De Man, B, and Samei, E. "Estimation of Radiation Dose in CT Based on Projection Data." Journal of digital imaging 29.5 (October 2016): 615-621.
PMID
26893140
Source
epmc
Published In
Journal of Digital Imaging
Volume
29
Issue
5
Publish Date
2016
Start Page
615
End Page
621
DOI
10.1007/s10278-016-9869-x

Patient-specific quantification of image quality: An automated method for measuring spatial resolution in clinical CT images.

To develop and validate an automated technique for evaluating the spatial resolution characteristics of clinical computed tomography (CT) images.Twenty one chest and abdominopelvic clinical CT datasets were examined in this study. An algorithm was developed to extract a CT resolution index (RI) analogous to the modulation transfer function from clinical CT images by measuring the edge-spread function (ESF) across the patient's skin. A polygon mesh of the air-skin boundary was created. The faces of the mesh were then used to measure the ESF across the air-skin interface. The ESF was differentiated to obtain the line-spread function (LSF), and the LSF was Fourier transformed to obtain the RI. The algorithm's ability to detect the radial dependence of the RI was investigated. RIs measured with the proposed method were compared with a conventional phantom-based method across two reconstruction algorithms (FBP and iterative) using the spatial frequency at 50% RI, f50, as the metric for comparison. Three reconstruction kernels were investigated for each reconstruction algorithm. Finally, an observer study was conducted to determine if observers could visually perceive the differences in the measured blurriness of images reconstructed with a given reconstruction method.RI measurements performed with the proposed technique exhibited the expected dependencies on the image reconstruction. The measured f50 values increased with harder kernels for both FBP and iterative reconstruction. Furthermore, the proposed algorithm was able to detect the radial dependence of the RI. Patient-specific measurements of the RI were comparable to the phantom-based technique, but the patient data exhibited a large spread in the measured f50, indicating that some datasets were blurrier than others even when the projection data were reconstructed with the same reconstruction algorithm and kernel. Results from the observer study substantiated this finding.Clinically informed, patient-specific spatial resolution can be measured from clinical datasets. The method is sufficiently sensitive to reflect changes in spatial resolution due to different reconstruction parameters. The method can be applied to automatically assess the spatial resolution of patient images and quantify dependencies that may not be captured in phantom data.

Authors
Sanders, J; Hurwitz, L; Samei, E
MLA Citation
Sanders, J, Hurwitz, L, and Samei, E. "Patient-specific quantification of image quality: An automated method for measuring spatial resolution in clinical CT images." Medical physics 43.10 (October 2016): 5330-.
PMID
27782718
Source
epmc
Published In
Medical physics
Volume
43
Issue
10
Publish Date
2016
Start Page
5330
DOI
10.1118/1.4961984

Assessing task performance in FFDM, DBT, and synthetic mammography using uniform and anthropomorphic physical phantoms.

The purpose of this study is to quantify the differences in detectability between full field digital mammography (FFDM), digital breast tomosynthesis (DBT), and synthetic mammography (SM) for challenging, low contrast signals, in the context of both a uniform and an anthropomorphic, textured phantom.Images of the phantoms were acquired using a Hologic Selenia Dimensions system. Images were taken at 50%, 100%, and 200% of the dose delivered under automatic exposure control (AEC). Low-contrast disks, created using an inkjet printer with iodine-doped ink, were inserted into the phantom. The disks varied in diameter from 210 to 630 μm, and in local contrast from 1.1% to 2.8% in regular increments. Human observers located the disks in a 4 alternative forced choice experiment. Proportion correct (PC) was computed as the number of correct localizations out of the total number of tries.Overall, scores from FFDM and DBT were consistently greater than scores from SM. At an exposure corresponding to the AEC setting, mean PC scores for the largest disks with the uniform phantom were 0.80 for FFDM, 0.83 for DBT, and 0.66 for SM, with the same rank ordering at other doses. Scores were similar but lower for the nonuniform background. At an exposure twice the AEC setting, however, the difference between uniform and nonuniform scores was most pronounced for DBT alone. Differences between scores for FFDM and SM were statistically significant, while those between FFDM and DBT were not. Scores were used to compute the minimum contrast level needed to reach 62.5% detection rate. The minimum contrast for SM was 36%-81% higher compared to FFDM or DBT, in either background.This study shows that an anthropomorphic phantom and lesions inserts may be used to conduct a reader study. Detectability was significantly lower for synthetic mammography than for FFDM or DBT, for all conditions. Additionally, observer performance was consistently lower for the anthropomorphic phantom, indicating the greater challenge due to anatomical background. Because of this, it may be important to use realistic phantoms in observer studies in order to draw conclusions that are more clinically relevant.

Authors
Ikejimba, LC; Glick, SJ; Choudhury, KR; Samei, E; Lo, JY
MLA Citation
Ikejimba, LC, Glick, SJ, Choudhury, KR, Samei, E, and Lo, JY. "Assessing task performance in FFDM, DBT, and synthetic mammography using uniform and anthropomorphic physical phantoms." Medical physics 43.10 (October 2016): 5593-.
PMID
27782687
Source
epmc
Published In
Medical physics
Volume
43
Issue
10
Publish Date
2016
Start Page
5593
DOI
10.1118/1.4962475

Technical Note: Gray tracking in medical color displays-A report of Task Group 196.

The authors discuss measurement methods and instrumentation useful for the characterization of the gray tracking performance of medical color monitors for diagnostic applications. The authors define gray tracking as the variability in the chromaticity of the gray levels in a color monitor.The authors present data regarding the capability of color measurement instruments with respect to their abilities to measure a target white point corresponding to the CIE Standard Illuminant D65 at different luminance values within the grayscale palette of a medical display. The authors then discuss evidence of significant differences in performance among color measurement instruments currently available for medical physicists to perform calibrations and image quality checks for the consistent representation of color in medical displays. In addition, the authors introduce two metrics for quantifying grayscale chromaticity consistency of gray tracking.The authors' findings show that there is an order of magnitude difference in the accuracy of field and reference instruments. The gray tracking metrics quantify how close the grayscale chromaticity is to the chromaticity of the full white point (equal amounts of red, green, and blue at maximum level) or to consecutive levels (equal values for red, green, and blue), with a lower value representing an improved grayscale tracking performance. An illustrative example of how to calculate and report the gray tracking performance according to the Task Group definitions is provided.The authors' proposed methodology for characterizing the grayscale degradation in chromaticity for color monitors that can be used to establish standards and procedures aiding in the quality control testing of color displays and color measurement instrumentation.

Authors
Badano, A; Wang, J; Boynton, P; Le Callet, P; Cheng, W-C; Deroo, D; Flynn, MJ; Matsui, T; Penczek, J; Revie, C; Samei, E; Steven, PM; Swiderski, S; Van Hoey, G; Yamaguchi, M; Hasegawa, M; Nagy, BV
MLA Citation
Badano, A, Wang, J, Boynton, P, Le Callet, P, Cheng, W-C, Deroo, D, Flynn, MJ, Matsui, T, Penczek, J, Revie, C, Samei, E, Steven, PM, Swiderski, S, Van Hoey, G, Yamaguchi, M, Hasegawa, M, and Nagy, BV. "Technical Note: Gray tracking in medical color displays-A report of Task Group 196." Medical physics 43.7 (July 2016): 4017-.
PMID
27370120
Source
epmc
Published In
Medical physics
Volume
43
Issue
7
Publish Date
2016
Start Page
4017
DOI
10.1118/1.4953186

Development and validation of a segmentation-free polyenergetic algorithm for dynamic perfusion computed tomography.

Dynamic perfusion imaging can provide the morphologic details of the scanned organs as well as the dynamic information of blood perfusion. However, due to the polyenergetic property of the x-ray spectra, beam hardening effect results in undesirable artifacts and inaccurate CT values. To address this problem, this study proposes a segmentation-free polyenergetic dynamic perfusion imaging algorithm (pDP) to provide superior perfusion imaging. Dynamic perfusion usually is composed of two phases, i.e., a precontrast phase and a postcontrast phase. In the precontrast phase, the attenuation properties of diverse base materials (e.g., in a thorax perfusion exam, base materials can include lung, fat, breast, soft tissue, bone, and metal implants) can be incorporated to reconstruct artifact-free precontrast images. If patient motions are negligible or can be corrected by registration, the precontrast images can then be employed as a priori information to derive linearized iodine projections from the postcontrast images. With the linearized iodine projections, iodine perfusion maps can be reconstructed directly without the influence of various influential factors, such as iodine location, patient size, x-ray spectrum, and background tissue type. A series of simulations were conducted on a dynamic iodine calibration phantom and a dynamic anthropomorphic thorax phantom to validate the proposed algorithm. The simulations with the dynamic iodine calibration phantom showed that the proposed algorithm could effectively eliminate the beam hardening effect and enable quantitative iodine map reconstruction across various influential factors. The error range of the iodine concentration factors ([Formula: see text]) was reduced from [Formula: see text] for filtered back-projection (FBP) to [Formula: see text] for pDP. The quantitative results of the simulations with the dynamic anthropomorphic thorax phantom indicated that the maximum error of iodine concentrations can be reduced from [Formula: see text] for FBP to less than [Formula: see text] for pDP, which suggested that the proposed algorithm could not only effectively eliminate beam hardening artifacts but also significantly reduce the influence of the metal artifacts and accurately reconstruct the iodine map regardless of the influential factors. A segmentation-free polyenergetic dynamic perfusion imaging algorithm was proposed and validated via simulations. This method can accurately reconstruct artifact-free iodine maps for quantitative analyses.

Authors
Lin, Y; Samei, E
MLA Citation
Lin, Y, and Samei, E. "Development and validation of a segmentation-free polyenergetic algorithm for dynamic perfusion computed tomography." Journal of medical imaging (Bellingham, Wash.) 3.3 (July 2016): 033503-.
PMID
27610396
Source
epmc
Published In
Journal of medical imaging (Bellingham, Wash.)
Volume
3
Issue
3
Publish Date
2016
Start Page
033503
DOI
10.1117/1.jmi.3.3.033503

Impact of breast structure on lesion detection in breast tomosynthesis, a simulation study.

This study aims to characterize the effect of background tissue density and heterogeneity on the detection of irregular masses in breast tomosynthesis, while demonstrating the capability of the sophisticated tools that can be used in the design, implementation, and performance analysis of virtual clinical trials (VCTs). Twenty breast phantoms from the extended cardiac-torso (XCAT) family, generated based on dedicated breast computed tomography of human subjects, were used to extract a total of 2173 volumes of interest (VOIs) from simulated tomosynthesis images. Five different lesions, modeled after human subject tomosynthesis images, were embedded in the breasts and combined with the lesion absent condition yielded a total of [Formula: see text] VOIs. Effects of background tissue density and heterogeneity on the detection of the lesions were studied by implementing a composite hypothesis signal detection paradigm with location known exactly, lesion known exactly or statistically, and background known statistically. Using the area under the receiver operating characteristic curve, detection performance deteriorated as density was increased, yielding findings consistent with clinical studies. A human observer study was performed on a subset of the simulated tomosynthesis images, confirming the detection performance trends with respect to density and serving as a validation of the implemented detector. Performance of the implemented detector varied substantially across the 20 breasts. Furthermore, background tissue density and heterogeneity affected the log-likelihood ratio test statistic differently under lesion absent and lesion present conditions. Therefore, considering background tissue variability in tissue models can change the outcomes of a VCT and is hence of crucial importance. The XCAT breast phantoms have the potential to address this concern by offering realistic modeling of background tissue variability based on a wide range of human subjects, comprising various breast shapes, sizes, and densities.

Authors
Kiarashi, N; Nolte, LW; Lo, JY; Segars, WP; Ghate, SV; Solomon, JB; Samei, E
MLA Citation
Kiarashi, N, Nolte, LW, Lo, JY, Segars, WP, Ghate, SV, Solomon, JB, and Samei, E. "Impact of breast structure on lesion detection in breast tomosynthesis, a simulation study." Journal of medical imaging (Bellingham, Wash.) 3.3 (July 2016): 035504-.
PMID
27660807
Source
epmc
Published In
Journal of medical imaging (Bellingham, Wash.)
Volume
3
Issue
3
Publish Date
2016
Start Page
035504
DOI
10.1117/1.jmi.3.3.035504

Correlation between human detection accuracy and observer model-based image quality metrics in computed tomography.

The purpose of this study was to compare computed tomography (CT) low-contrast detectability from human readers with observer model-based surrogates of image quality. A phantom with a range of low-contrast signals (five contrasts, three sizes) was imaged on a state-of-the-art CT scanner (Siemens' force). Images were reconstructed using filtered back projection and advanced modeled iterative reconstruction and were assessed by 11 readers using a two alternative forced choice method. Concurrently, contrast-to-noise ratio (CNR), area-weighted CNR (CNRA), and observer model-based metrics were estimated, including nonprewhitening (NPW) matched filter, NPW with eye filter (NPWE), NPW with internal noise, NPW with an eye filter and internal noise (NPWEi), channelized Hotelling observer (CHO), and CHO with internal noise (CHOi). The correlation coefficients (Pearson and Spearman), linear discriminator error, [Formula: see text], and magnitude of confidence intervals, [Formula: see text], were used to determine correlation, proper characterization of the reconstruction algorithms, and model precision, respectively. Pearson (Spearman) correlation was 0.36 (0.33), 0.83 (0.84), 0.84 (0.86), 0.86 (0.88), 0.86 (0.91), 0.88 (0.90), 0.85 (0.89), and 0.87 (0.84), [Formula: see text] was 0.25, 0.15, 0.2, 0.25, 0.3, 0.25, 0.4, and 0.45, and [Formula: see text] was [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] for CNR, CNRA, NPW, NPWE, NPWi, NPWEi, CHO, and CHOi, respectively.

Authors
Solomon, J; Samei, E
MLA Citation
Solomon, J, and Samei, E. "Correlation between human detection accuracy and observer model-based image quality metrics in computed tomography." Journal of medical imaging (Bellingham, Wash.) 3.3 (July 2016): 035506-.
PMID
27704032
Source
epmc
Published In
Journal of medical imaging (Bellingham, Wash.)
Volume
3
Issue
3
Publish Date
2016
Start Page
035506

Variability in CT scanning over-range across clinical operation

Authors
Ria, F; Wilson, JM; Guntzer, P; Zanca, F; Samei, E
MLA Citation
Ria, F, Wilson, JM, Guntzer, P, Zanca, F, and Samei, E. "Variability in CT scanning over-range across clinical operation." 58th AAMP Annual Meeting. American Association of Physicists in Medicine: Medical Physics, June 30, 2016.
Source
manual
Published In
Medical physics
Volume
43
Issue
6
Publish Date
2016
Start Page
3397
End Page
3397

Effect of a Noise-Optimized Second-Generation Monoenergetic Algorithm on Image Noise and Conspicuity of Hypervascular Liver Tumors: An In Vitro and In Vivo Study.

The purpose of this study is to investigate whether the reduction in noise using a second-generation monoenergetic algorithm can improve the conspicuity of hypervascular liver tumors on dual-energy CT (DECT) images of the liver.An anthropomorphic liver phantom in three body sizes and iodine-containing inserts simulating hypervascular lesions was imaged with DECT and single-energy CT at various energy levels (80-140 kV). In addition, a retrospective clinical study was performed in 31 patients with 66 hypervascular liver tumors who underwent DECT during the late hepatic arterial phase. Datasets at energy levels ranging from 40 to 80 keV were reconstructed using first- and second-generation monoenergetic algorithms. Noise, tumor-to-liver contrast-to-noise ratio (CNR), and CNR with a noise constraint (CNRNC) set with a maximum noise increase of 50% were calculated and compared among the different reconstructed datasets.The maximum CNR for the second-generation monoenergetic algorithm, which was attained at 40 keV in both phantom and clinical datasets, was statistically significantly higher than the maximum CNR for the first-generation monoenergetic algorithm (p < 0.001) or single-energy CT acquisitions across a wide range of kilovoltage values. With the second-generation monoenergetic algorithm, the optimal CNRNC occurred at 55 keV, corresponding to lower energy levels compared with first-generation algorithm (predominantly at 70 keV). Patient body size did not substantially affect the selection of the optimal energy level to attain maximal CNR and CNRNC using the second-generation monoenergetic algorithm.A noise-optimized second-generation monoenergetic algorithm significantly improves the conspicuity of hypervascular liver tumors.

Authors
Marin, D; Ramirez-Giraldo, JC; Gupta, S; Fu, W; Stinnett, SS; Mileto, A; Bellini, D; Patel, B; Samei, E; Nelson, RC
MLA Citation
Marin, D, Ramirez-Giraldo, JC, Gupta, S, Fu, W, Stinnett, SS, Mileto, A, Bellini, D, Patel, B, Samei, E, and Nelson, RC. "Effect of a Noise-Optimized Second-Generation Monoenergetic Algorithm on Image Noise and Conspicuity of Hypervascular Liver Tumors: An In Vitro and In Vivo Study." AJR. American journal of roentgenology 206.6 (June 2016): 1222-1232.
PMID
27058192
Source
epmc
Published In
AJR. American journal of roentgenology
Volume
206
Issue
6
Publish Date
2016
Start Page
1222
End Page
1232
DOI
10.2214/ajr.15.15512

SU-F-I-48: Variability in CT Scanning Over-Range Across Clinical Operation.

Inconsistency in the scan range for a given protocol can be a source of variability in patient dose. The purpose of this study was to determine the variability in the over-scan length in clinical CT operation for chest and abdominopelvic (A&P) protocols.A total of 51 abdomen-pelvis and 121 chest CT exams were randomly selected from our clinical database. A commercial dose monitoring solution was used to extract and database the total exposure area and the geometrical information related to automatically-segmented anatomical landmarks for each target region. The data were exported off-line for the statistical analysis. The over-scan length (delta) was calculated as the difference between the real scanned length and ideal scanning length based on the anatomical landmarks for each target region.The mean delta for abdomen-pelvis exams was 12 mm (median 8 mm; min -191 mm; max 158 mm; standard deviation 71 mm). The average delta values at the interfaces with the chest and lower extremity regions were 69 mm and -57 mm, respectively. For chest exams, the average delta was 91 mm (median 93 mm; min 36 mm; max 190 mm; standard deviation 29 mm), and the average delta values at interfaces with the neck and abdomen regions were 26 mm and 65 mm, respectively. The percentage delta mean related to the abdomen-pelvis and chest lengths were 3% and 45%, respectively.Although there is greater over-scan in the chest region, there is considerably more variability in the over-scan area for abdomen-pelvis exams. Estimation of the over-scan length must be included in the effective dose estimates, which uses different coefficients for different target region (ICRP 102). Furthermore, knowledge of over-scan lengths and variability can guide steps to improve clinical consistency and operation.

Authors
Ria, F; Wilson, JM; Guntzer, P; Zanca, F; Samei, E
MLA Citation
Ria, F, Wilson, JM, Guntzer, P, Zanca, F, and Samei, E. "SU-F-I-48: Variability in CT Scanning Over-Range Across Clinical Operation." June 2016.
PMID
28048214
Source
epmc
Published In
Medical physics
Volume
43
Issue
6
Publish Date
2016
Start Page
3397
DOI
10.1118/1.4955876

SU-G-206-13: Validating Dose Split: A Method to Image the Same Patient at Multiple Doses with a Single CT Acquisition.

Dose optimization studies in CT have a need for images acquired at multiple dose levels. This presents ethical and logistical challenges for performing such research with human subjects. As a result, most studies rely on phantom data. The purpose of this study was to perform a physics-based validation of a method to obtain images of the same patient at multiple dose levels using a single CT acquisition on a dual-source CT system.The Dose Split (DS) method relies on acquiring raw projection data simultaneously from two separate sources/detectors (denoted Tube A and Tube B) on a dual-source system. By distributing the dose unevenly between Tube A and Tube B (at the same kVp), it is possible to reconstruct images corresponding to any dose in the range of min(A,B) to A+B. CT data of the ACR phantom were acquired on a dual-source system (SOMATOM Flash, Siemens Healthcare) with a traditional single-source (SS) technique at 6 dose levels (25, 50, 75, 100, 150, and 200 mAs). Corresponding data using the DS technique were acquired and compared with the SS data in terms of noise magnitude (pixel STD), contrast, contrast-to-noise ratio, noise power spectrum (average spatial frequency), modulation transfer function (50% frequency) and detectability index (for a non-prewhitening matched filter observer).Between the DS and SS techniques, the differences (SS-DS) in noise magnitude, contrast, and CNR were on average (across doses) 1.2 HU (4.1%), 0.7 HU (11%), and 0.02 (6.9%), respectively. The differences in NPS average frequency, MTF 50% frequency, and detectability index were 0.01 cycles/mm (2.5%), 0.03 cycles/mm (7.5%), and -.03 (-6.8%), respectively.The dose split method can be used to acquire images of the same patient equivalent to many dose levels in a single acquisition. Differences in noise, CNR, NPS, MTF, and detectability were all negligible.

Authors
Solomon, J; Zhang, Y; Marin, D; Samei, E
MLA Citation
Solomon, J, Zhang, Y, Marin, D, and Samei, E. "SU-G-206-13: Validating Dose Split: A Method to Image the Same Patient at Multiple Doses with a Single CT Acquisition." Medical physics 43.6 (June 2016): 3642-.
PMID
28046817
Source
epmc
Published In
Medical physics
Volume
43
Issue
6
Publish Date
2016
Start Page
3642
DOI
10.1118/1.4956954

SU-F-R-11: Designing Quality and Safety Informatics Through Implementation of a CT Radiation Dose Monitoring Program.

Recent legislative and accreditation requirements have driven rapid development and implementation of CT radiation dose monitoring solutions. Institutions must determine how to improve quality, safety, and consistency of their clinical performance. The purpose of this work was to design a strategy and meaningful characterization of results from an in-house, clinically-deployed dose monitoring solution.A dose monitoring platform was designed by our imaging physics group that focused on extracting protocol parameters, dose metrics, and patient demographics and size. Compared to most commercial solutions, which focus on individual exam alerts and global thresholds, the program sought to characterize overall consistency and targeted thresholds based on eight analytic interrogations. Those were based on explicit questions related to protocol application, national benchmarks, protocol and size-specific dose targets, operational consistency, outliers, temporal trends, intra-system variability, and consistent use of electronic protocols. Using historical data since the start of 2013, 95% and 99% intervals were used to establish yellow and amber parameterized dose alert thresholds, respectively, as a function of protocol, scanner, and size.Quarterly reports have been generated for three hospitals for 3 quarters of 2015 totaling 27880, 28502, 30631 exams, respectively. Four adult and two pediatric protocols were higher than external institutional benchmarks. Four protocol dose levels were being inconsistently applied as a function of patient size. For the three hospitals, the minimum and maximum amber outlier percentages were [1.53%,2.28%], [0.76%,1.8%], [0.94%,1.17%], respectively. Compared with the electronic protocols, 10 protocols were found to be used with some inconsistency.Dose monitoring can satisfy requirements with global alert thresholds and patient dose records, but the real value is in optimizing patient-specific protocols, balancing image quality trade-offs that dose-reduction strategies promise, and improving the performance and consistency of a clinical operation. Data plots that capture patient demographics and scanner performance demonstrate that value.

Authors
Wilson, JM; Samei, E
MLA Citation
Wilson, JM, and Samei, E. "SU-F-R-11: Designing Quality and Safety Informatics Through Implementation of a CT Radiation Dose Monitoring Program." Medical physics 43.6 (June 2016): 3375-.
PMID
28048918
Source
epmc
Published In
Medical physics
Volume
43
Issue
6
Publish Date
2016
Start Page
3375
DOI
10.1118/1.4955783

TU-FG-209-07: Medical Physics 1.0 Versus Medical Physics 2.0: A Case Study.

To illustrate how performance analytics can identify performance decrement in digital radiography systems.Subsequent to a radiologist's image quality complaint, four different advanced methods contributed to root cause analysis. Our system was a GE Revolution XQi digital radiography unit. Initially, we reviewed weekly GE Quality Assurance Procedures (QAP) results in a database dating from 2001. Next, we evaluated objective image quality metrics of individual PA Chest radiographs acquired. These images were anonymized, securely transferred, and analyzed by the Duke University Clinical Imaging Physics Group with software previously described1 and validated2 . Third, we compared the exposure-dependent SNR2 (NEQ) of the unit with previously established confidence limits3 . Finally, we explored our service database to reveal events that might affect detector performance.QAP reported a decrease in CNR reflected in a significant increase in lung noise(Ln), mediastinum noise(Mn), and subdiaphragm-lung contrast(Slc) with a significant decrease in lung grey level(Lgl) after detector replacement. Most change occurred during week 1, before the QAP indicated one-half the ultimate decrease in CNR. After detector recalibration, QAP CNR improved, but was not restored to previous levels. Lgl and Slc were no longer significantly different from before, however Ln and Mn remained significantly different. Exposure-dependent SNR2 show the detector to be operating within limits in October 2006 but subsequently became miscalibrated sometime before acquisition of the 2011-2014 data. Service records revealed catastrophic failure of the Image Detection Controller that contained the 2007 calibration. Traditional metrics did not indicate that the system was performing outside of normal limits.Performance analytics are powerful tools whose proper application could allow early intervention in degraded system performance. The image-quality metrics appear to be highly sensitive to system performance and are reported with every acquisition rather than at arbitrary intervals. Confidence intervals may require customization for individual systems or detectors.

Authors
Carver, D; Willis, C; Stauduhar, P; Nishino, T; Wells, J; Samei, E
MLA Citation
Carver, D, Willis, C, Stauduhar, P, Nishino, T, Wells, J, and Samei, E. "TU-FG-209-07: Medical Physics 1.0 Versus Medical Physics 2.0: A Case Study." Medical physics 43.6 (June 2016): 3762-.
PMID
28048675
Source
epmc
Published In
Medical physics
Volume
43
Issue
6
Publish Date
2016
Start Page
3762
DOI
10.1118/1.4957577

TH-CD-207B-04: Is TTF a True Representation of the Sharpness Property of a Non-Linear CT System?

To investigate if the task-transfer-function (TTF) accurately models the transfer properties of a CT system for lung nodule imaging.An anthropomorphic lung phantom was imaged using a standard chest protocol on a clinical CT scanner with and without 24 physically inserted synthetic lesions (nominal diameter: 8 - 10 mm). Images were reconstructed using FBP and iterative algorithm (SAFIRE, Siemens Healthcare). 3D TTF was measured using an established technique. Corresponding idealized virtual lesions were blurred with the TTF and superimposed onto lesion-less phantom images. Images of the physically and virtually inserted lesions were compared in terms of rendition of spatial features (blurriness of the edges), lesion morphology, and lesion volume. Feature rendition was measured in terms root-mean-square (RMS) of the frequency power of the native and TTF-transferred lesion edge transition. Morphology was assessed with the Regional Hausdorff Distance (RHD) using custom written code (MATLAB v2015b). Volumes were measured using a clinical segmentation tool (iNtution, TeraRecon).The RMS was less than 0.02 and 0.05 for FBP and IR respectively. Using the nonlinear mixed effect (nlme) package (R, www.r-project.org), the difference in RHD between virtual and physical lesions was 5% on average. There was less than 1 ± 5% (R2 > 0.97) and 3 ± 4% (R2 > 0.97) difference between the volumes of the physical lesions and the corresponding virtual lesions for FBP and IR respectively. Additionally, was closer concordance for images reconstructed with FBP than iterative reconstruction.The TTF was found to accurately model the transfer properties of the CT imaging system on lung lesions for both FBP and iterative reconstruction algorithms. TTF was found to offer slightly better lesion renditions when modeling images reconstructed with FBP versus iterative reconstruction. This methodology will be used in future investigation of more complex imaging tasks such as low contrast detectability of known lesions.

Authors
Robins, M; Solomon, J; Samei, E
MLA Citation
Robins, M, Solomon, J, and Samei, E. "TH-CD-207B-04: Is TTF a True Representation of the Sharpness Property of a Non-Linear CT System?." Medical physics 43.6 (June 2016): 3889-.
PMID
28048150
Source
epmc
Published In
Medical physics
Volume
43
Issue
6
Publish Date
2016
Start Page
3889
DOI
10.1118/1.4958210

TH-CD-207B-02: An Automated Technique to Measure Spatial Resolution in Clinical CT Images: Application to Patient Data.

To evaluate an automated technique for measuring spatial resolution across a database of clinical CT exams.A fully automated algorithm was developed to extract a CT resolution index (RI) analogous to the modulation transfer function from clinical CT images by measuring the edge-spread function (ESF) across the patient's skin and converting the results into scalar values, frequency at 50% RI, f50. The program was previously validated against observer data. This algorithm was applied to a database of CT images from our hospital that were reconstructed with different reconstruction algorithms (filtered back-projection and iterative) and reconstruction kernels (soft and hard). The results were analyzed in terms of mean and variability within reconstruction methods and kernel aspects of the protocols.The automated algorithm successfully measured the RI index from all of the clinical datasets examined. The measured f50 values increased with harder kernels for both FBP and iterative reconstruction. The mean f50 was 0.30 ± 0.02 mm-1 and 0.42 ± 0.03 mm-1 for images reconstructed with soft and hard kernels, respectively, using filtered back-projection. The corresponding values for iterative reconstructions were 0.34 ± 0.02 mm-1 and 0.39 ± 0.03 mm-1, respectively. Overall, there was more variability in the f50 measurements made on datasets reconstructed with a hard kernel. The differences were statistically significant (p<0.05).Clinically-informed, patient-specific spatial resolution can be measured from clinical datasets. The method is sufficiently sensitive to reflect changes in spatial resolution due to different reconstruction parameters. The method can be applied to automatically assess the spatial resolution of patient images and quantify dependencies that may not be captured in phantom data.

Authors
Sanders, J; Ding, A; Samei, E
MLA Citation
Sanders, J, Ding, A, and Samei, E. "TH-CD-207B-02: An Automated Technique to Measure Spatial Resolution in Clinical CT Images: Application to Patient Data." Medical physics 43.6 (June 2016): 3889-.
PMID
28047694
Source
epmc
Published In
Medical physics
Volume
43
Issue
6
Publish Date
2016
Start Page
3889
DOI
10.1118/1.4958208

SU-F-I-45: An Automated Technique to Measure Image Contrast in Clinical CT Images.

To develop and validate an automated technique for measuring image contrast in chest computed tomography (CT) exams.An automated computer algorithm was developed to measure the distribution of Hounsfield units (HUs) inside four major organs: the lungs, liver, aorta, and bones. These organs were first segmented or identified using computer vision and image processing techniques. Regions of interest (ROIs) were automatically placed inside the lungs, liver, and aorta and histograms of the HUs inside the ROIs were constructed. The mean and standard deviation of each histogram were computed for each CT dataset. Comparison of the mean and standard deviation of the HUs in the different organs provides different contrast values. The ROI for the bones is simply the segmentation mask of the bones. Since the histogram for bones does not follow a Gaussian distribution, the 25th and 75th percentile were computed instead of the mean. The sensitivity and accuracy of the algorithm was investigated by comparing the automated measurements with manual measurements. Fifteen contrast enhanced and fifteen non-contrast enhanced chest CT clinical datasets were examined in the validation procedure.The algorithm successfully measured the histograms of the four organs in both contrast and non-contrast enhanced chest CT exams. The automated measurements were in agreement with manual measurements. The algorithm has sufficient sensitivity as indicated by the near unity slope of the automated versus manual measurement plots. Furthermore, the algorithm has sufficient accuracy as indicated by the high coefficient of determination, R2, values ranging from 0.879 to 0.998.Patient-specific image contrast can be measured from clinical datasets. The algorithm can be run on both contrast enhanced and non-enhanced clinical datasets. The method can be applied to automatically assess the contrast characteristics of clinical chest CT images and quantify dependencies that may not be captured in phantom data.

Authors
Sanders, J; Abadi, E; Meng, B; Samei, E
MLA Citation
Sanders, J, Abadi, E, Meng, B, and Samei, E. "SU-F-I-45: An Automated Technique to Measure Image Contrast in Clinical CT Images." Medical physics 43.6 (June 2016): 3397-.
PMID
28047457
Source
epmc
Published In
Medical physics
Volume
43
Issue
6
Publish Date
2016
Start Page
3397
DOI
10.1118/1.4955873

TU-H-207A-05: Automated Early Identification of An Excessive Air-In-Oil X-Ray Tube Artifact That Mimics Acute Cerebral Infarct.

There is an infrequent but serious CT artifact that occurs when there is too much air in the cooling oil of an x-ray tube. This artifact manifests as patchy hypodensities and mimics acute cerebral infarct. Routine quality control testing is unlikely to detect this artifact before it is observed in patient images. The purpose of this project was to develop an automated, quantitative method that increased the likelihood of identifying and preventing such artifacts.Using QC phantom images with a known air-in-oil artifact, a 1D radial representation of the 2D noise power spectrum(NPS) was calculated and compared against that for artifact-free images. The QC program software used at our institution to analyze daily phantom images was modified to include measuring the average frequency of NPS within the water section of daily phantom scans. The threshold values developed for each CT system were incorporated into our daily QC program and email notification system.The NPS for the known air-in-oil artifact images included a large low frequency peak compared with artifact-free images; the average NPS frequency for these images were 0.197 and 0.319 (1/mm), respectively. The average NPS frequency values (mean+/- standard deviation) for the GE CT750, GE VCT, GE Lightspeed Xtra, and Siemens SOMATOM Definition Flash scanners were 0.322+/- 0.0058, 0.324+/-0.0024, 0.320+/-0.0020, and 0.303+/-0.0039 (1/mm), respectively. Threshold values were chosen to be the average plus or minus twice the standard deviation. Automated QC successfully identified an air-in-oil artifact in the Lightspeed Xtra before any detrimental clinical effect occurred; the average NPS frequency value that triggered service was 0.307, which is six standard deviations smaller than average.Clinically serious problems associated with the air-in-oil artifact can be detected earlier and mitigated/avoided by incorporating the average frequency of NPS measurements of daily phantom images into an automated QC program.

Authors
Winslow, J; Zhang, Y; Samei, E
MLA Citation
Winslow, J, Zhang, Y, and Samei, E. "TU-H-207A-05: Automated Early Identification of An Excessive Air-In-Oil X-Ray Tube Artifact That Mimics Acute Cerebral Infarct." Medical physics 43.6 (June 2016): 3772-.
PMID
28047181
Source
epmc
Published In
Medical physics
Volume
43
Issue
6
Publish Date
2016
Start Page
3772
DOI
10.1118/1.4957641

TU-H-207A-09: An Automated Technique for Estimating Patient-Specific Regional Imparted Energy and Dose From TCM CT Exams Across 13 Protocols.

To develop an automated technique for estimating patient-specific regional imparted energy and dose from tube current modulated (TCM) computed tomography (CT) exams across a diverse set of head and body protocols.A library of 58 adult computational anthropomorphic extended cardiac-torso (XCAT) phantoms were used to model a patient population. A validated Monte Carlo program was used to simulate TCM CT exams on the entire library of phantoms for three head and 10 body protocols. The net imparted energy to the phantoms, normalized by dose length product (DLP), and the net tissue mass in each of the scan regions were computed. A knowledgebase containing relationships between normalized imparted energy and scanned mass was established. An automated computer algorithm was written to estimate the scanned mass from actual clinical CT exams. The scanned mass estimate, DLP of the exam, and knowledgebase were used to estimate the imparted energy to the patient. The algorithm was tested on 20 chest and 20 abdominopelvic TCM CT exams.The normalized imparted energy increased with increasing kV for all protocols. However, the normalized imparted energy was relatively unaffected by the strength of the TCM. The average imparted energy was 681 ± 376 mJ for abdominopelvic exams and 274 ± 141 mJ for chest exams. Overall, the method was successful in providing patientspecific estimates of imparted energy for 98% of the cases tested.Imparted energy normalized by DLP increased with increasing tube potential. However, the strength of the TCM did not have a significant effect on the net amount of energy deposited to tissue. The automated program can be implemented into the clinical workflow to provide estimates of regional imparted energy and dose across a diverse set of clinical protocols.

Authors
Sanders, J; Tian, X; Segars, P; Boone, J; Samei, E
MLA Citation
Sanders, J, Tian, X, Segars, P, Boone, J, and Samei, E. "TU-H-207A-09: An Automated Technique for Estimating Patient-Specific Regional Imparted Energy and Dose From TCM CT Exams Across 13 Protocols." Medical physics 43.6 (June 2016): 3773-.
PMID
28047247
Source
epmc
Published In
Medical physics
Volume
43
Issue
6
Publish Date
2016
Start Page
3773
DOI
10.1118/1.4957645

TU-D-207A-02: Quantitative Assessment of CT Systems with Iterative Image Reconstruction Algorithms.

In recent several years, motivated by the need to reduce radiation doses in CT exams, all of the major CT manufacturers have commercialized different iterative image reconstruction techniques and these innovative techniques were used in clinical routines with increasing popularity. However, due to the intrinsic nonlinearity of these new techniques, the well accepted quantitative image quality assessment metrics such as spatial resolution and contrast to noise ratio are not sufficient to provide the needed quantitative metrics for assessing image quality and for guiding the CT scan protocol optimization. This symposium aims at providing a thorough update to AAPM community on what we have understood in the past for linear CT imaging system, what are the new challenges and opportunities offered by the nonlinear iterative image reconstruction, and what would be the future directions in quantitative image quality assessment that the AAPM community can work together to address the challenges and to adapt the nonlinear image reconstruction methods to routine clinical practice to improve patient care. Three invited speakers will lead the discussions in this symposium. Dr. Ke Li from the University of Wisconsin-Madison will be presenting the new challenges introduced in model-based iterative reconstruction (MBIR) method with a focus on how the nonlinear nature of the MBIR reconstruction poses challenges in quantitative image quality metrics such as spatial resolution, noise power spectrum, and the limitations of CNR in protocol optimization which eventually leads to the need of task-based detectability index as the metric. Dr. Shuai Leng from Mayo Clinic will then present how the CNR metric is insufficient for nonlinear reconstruction algorithms, and how task based model observers can be used to more accurately quantify image quality, and to optimize imaging system and scanning protocols for nonlinear iterative image reconstruction algorithms based on specific imaging task. Practical considerations regarding the application of task based image quality metrics will also be discussed. Dr. Ehsan Samei from Duke University will start the symposium by summarizing a to-be-released AAPM Task Group report (TG 233: Performance Evaluation of Computed Tomography Systems). He will cover what has been understood and accepted for linear CT imaging system, what are the new challenges in CT image quality assessment introduced by the nonlinear iterative reconstruction (IR) techniques, and summarize both taskneutral and task-based metrologies developed in TG 233 to partially address these challenges, and foresee additional challenges in the future.1. Understand the challenges in quantitative image quality assessment introduced by nonlinear iterative reconstruction techniques 2. Understand the challenges and methods in noise performance assessment for nonlinear iterative reconstruction techniques 3. Understand the challenges and methods in in spatial resolution assessment for nonlinear iterative reconstruction techniques 4. Understand the challenges and methods in in task-based observer performance assessment for nonlinear iterative reconstruction techniques Funding support received from NIH and DOD; Funding support received from GE Healthcare; Funding support received from Siemens AX; Patent royalties received from GE Healthcare; S. Leng, R01 EB071095; U01 EB017185; E. Samei, Research grant, Siemens; Research grant, GE; K. Li, Funding from NIH, DOD and AAPM.

Authors
Samei, E
MLA Citation
Samei, E. "TU-D-207A-02: Quantitative Assessment of CT Systems with Iterative Image Reconstruction Algorithms." Medical physics 43.6 (June 2016): 3747-3748.
PMID
28046664
Source
epmc
Published In
Medical physics
Volume
43
Issue
6
Publish Date
2016
Start Page
3747
End Page
3748
DOI
10.1118/1.4957495

TU-FG-209-06: Quantitative Evaluation of the Temporal Performance of Clinical Fluoroscopic Imaging Systems: The Temporal Modulation Transfer Function (TMTF).

Measure the temporal modulation transfer function (TMTF) of clinical fluoroscopic flat panel imaging systems in order to accurately quantify their performance for temporally sensitive clinical tasks.Copper blades (0.76 mm thick, 6 cm radius) with precision-machined edges were manufactured and mounted on a voltage regulated DC motor apparatus. Images were acquired with the blade apparatus positioned at the center of the detector matrix and set in motion at a constant rotational velocity (0.66 Hz), thereby creating a rotating radio-opaque edge in both space and time. The spatio-temporal edge response function was analyzed using a single frame from the acquired image sequence. Image processing included semi-automatic detection of the center of rotation, rebinning the pixels into subsampled polar coordinates, and deconvolving the TMTF from the previously measured spatial MTF. The analysis returned the presampled TMTF. This method was applied to multiple fluoroscopic imaging systems.Initial experiments measured the TMTF of a typical fluoroscopy unit (Philips Allura Xper FD20) using cine acquisition (60.7 kVp, 6 fps, 42.6 ms pulse-width). For this system and protocol, the measured TMTF closely matched an idealized sinc function corresponding to the Fourier transform of the measured rectangular x-ray pulse-width. Within the frequency range of 0 - 47 Hz, the measured TMTF and ideal sinc function were compared at 1.46 Hz intervals. The differences measured varied within [-0.0164, 0.0324] with a root-mean-square (rms) difference of 0.0201. These particular results suggest that very little degradation in temporal performance is attributable to the imaging hardware, but rather the measured performance is dominated by the acquisition protocol parameters, namely pulse-width and frames-per-second.This method provides a clinically tractable and accurate measurement of the TMTF. Ongoing experiments are investigating the impact of different fluoroscopy systems, image processing, and protocol choice on the measured TMTF.

Authors
Richards, T; Mann, S; Samei, E
MLA Citation
Richards, T, Mann, S, and Samei, E. "TU-FG-209-06: Quantitative Evaluation of the Temporal Performance of Clinical Fluoroscopic Imaging Systems: The Temporal Modulation Transfer Function (TMTF)." Medical physics 43.6 (June 2016): 3761-3762.
PMID
28046623
Source
epmc
Published In
Medical physics
Volume
43
Issue
6
Publish Date
2016
Start Page
3761
End Page
3762
DOI
10.1118/1.4957576

TU-H-206-01: An Automated Approach for Identifying Geometric Distortions in Gamma Cameras.

To develop a clinically-deployable, automated process for detecting artifacts in routine nuclear medicine (NM) quality assurance (QA) bar phantom images.An artifact detection algorithm was created to analyze bar phantom images as part of an ongoing QA program. A low noise, high resolution reference image was acquired from an x-ray of the bar phantom with a Philips Digital Diagnost system utilizing image stitching. NM bar images, acquired for 5 million counts over a 512×512 matrix, were registered to the template image by maximizing mutual information (MI). The MI index was used as an initial test for artifacts; low values indicate an overall presence of distortions regardless of their spatial location. Images with low MI scores were further analyzed for bar linearity, periodicity, alignment, and compression to locate differences with respect to the template. Findings from each test were spatially correlated and locations failing multiple tests were flagged as potential artifacts requiring additional visual analysis. The algorithm was initially deployed for GE Discovery 670 and Infinia Hawkeye gamma cameras.The algorithm successfully identified clinically relevant artifacts from both systems previously unnoticed by technologists performing the QA. Average MI indices for artifact-free images are 0.55. Images with MI indices < 0.50 have shown 100% sensitivity and specificity for artifact detection when compared with a thorough visual analysis. Correlation of geometric tests confirms the ability to spatially locate the most likely image regions containing an artifact regardless of initial phantom orientation.The algorithm shows the potential to detect gamma camera artifacts that may be missed by routine technologist inspections. Detection and subsequent correction of artifacts ensures maximum image quality and may help to identify failing hardware before it impacts clinical workflow. Going forward, the algorithm is being deployed to monitor data from all gamma cameras within our health system.

Authors
Mann, S; Nelson, J; Samei, E
MLA Citation
Mann, S, Nelson, J, and Samei, E. "TU-H-206-01: An Automated Approach for Identifying Geometric Distortions in Gamma Cameras." Medical physics 43.6 (June 2016): 3773-3774.
PMID
28046574
Source
epmc
Published In
Medical physics
Volume
43
Issue
6
Publish Date
2016
Start Page
3773
End Page
3774
DOI
10.1118/1.4957646

WE-B-BRC-03: Risk in the Context of Medical Imaging.

Prospective quality management techniques, long used by engineering and industry, have become a growing aspect of efforts to improve quality management and safety in healthcare. These techniques are of particular interest to medical physics as scope and complexity of clinical practice continue to grow, thus making the prescriptive methods we have used harder to apply and potentially less effective for our interconnected and highly complex healthcare enterprise, especially in imaging and radiation oncology. An essential part of most prospective methods is the need to assess the various risks associated with problems, failures, errors, and design flaws in our systems. We therefore begin with an overview of risk assessment methodologies used in healthcare and industry and discuss their strengths and weaknesses. The rationale for use of process mapping, failure modes and effects analysis (FMEA) and fault tree analysis (FTA) by TG-100 will be described, as well as suggestions for the way forward. This is followed by discussion of radiation oncology specific risk assessment strategies and issues, including the TG-100 effort to evaluate IMRT and other ways to think about risk in the context of radiotherapy. Incident learning systems, local as well as the ASTRO/AAPM ROILS system, can also be useful in the risk assessment process. Finally, risk in the context of medical imaging will be discussed. Radiation (and other) safety considerations, as well as lack of quality and certainty all contribute to the potential risks associated with suboptimal imaging. The goal of this session is to summarize a wide variety of risk analysis methods and issues to give the medical physicist access to tools which can better define risks (and their importance) which we work to mitigate with both prescriptive and prospective risk-based quality management methods.1. Description of risk assessment methodologies used in healthcare and industry 2. Discussion of radiation oncology-specific risk assessment strategies and issues 3. Evaluation of risk in the context of medical imaging and image quality E. Samei: Research grants from Siemens and GE.

Authors
Samei, E
MLA Citation
Samei, E. "WE-B-BRC-03: Risk in the Context of Medical Imaging." Medical physics 43.6 (June 2016): 3807-.
PMID
28046258
Source
epmc
Published In
Medical physics
Volume
43
Issue
6
Publish Date
2016
Start Page
3807
DOI
10.1118/1.4957800

TH-AB-207A-01: Contrast-Enhanced CT: Correlation of Radiation Dose and Biological Effect.

The potential risk from CT is generally characterized in terms of radiation dose. The presence of iodinated-contrast medium increases radiation dose. However, it is unclear how much of this increase is biologically relevant. The purpose of this study was to establish the contribution of dose increase from iodine to biological effect.Radiation organ dose was estimated in 58 human (XCAT) phantoms "undergoing" chest CT examination (120 kVp, 9 mGy CTDI) on a simulated CT system (Definition Flash, Siemens) with and without iodinated-contrast agent (62.5 mL of iodine per subject). The dose without and with the presence of iodine was compared to the increase in foci per cell (a surrogate of DNA damage) measured before and after similar CT exams without and with contrast agent (Piechowiak et al. 2015). The data were analyzed to ascertain how the enhancement in biological effect in contrast-enhanced CTs correlated with the increase in dose due to the presence of iodine.The presence of iodinated-contrast in CT increased the organ doses by 2% to 50% on average. Typical values were heart (50%±7%), kidney (19%±7%), and liver (2%±3%). The corresponding increase in the average foci per cell was 107%±19%, indicating biological effect of iodine was greater than what would be anticipated from the iodine-initiated increase in radiation dose alone.Mean foci per cell and organ dose both increase in the presence of contrast agent. The former, however, is at least twice as large as the latter, indicating that iodine contributes to an increase in the probability of DNA damage not only as a consequence of increased x-ray energy deposition but also from other mechanisms. Hence iodine radiation dose, while relevant to be included in estimating the risk associated with contrast-enhanced CT, still can underestimate the biological effects.

Authors
Abadi, E; Sanders, J; Agasthya, G; Segars, P; Samei, E
MLA Citation
Abadi, E, Sanders, J, Agasthya, G, Segars, P, and Samei, E. "TH-AB-207A-01: Contrast-Enhanced CT: Correlation of Radiation Dose and Biological Effect." Medical physics 43.6 (June 2016): 3859-.
PMID
28046510
Source
epmc
Published In
Medical physics
Volume
43
Issue
6
Publish Date
2016
Start Page
3859
DOI
10.1118/1.4958077

How does c-view image quality compare with conventional 2D FFDM?

The FDA approved the use of digital breast tomosynthesis (DBT) in 2011 as an adjunct to 2D full field digital mammography (FFDM) with the constraint that all DBT acquisitions must be paired with a 2D image to assure adequate interpretative information is provided. Recently manufacturers have developed methods to provide a synthesized 2D image generated from the DBT data with the hope of sparing patients the radiation exposure from the FFDM acquisition. While this much needed alternative effectively reduces the total radiation burden, differences in image quality must also be considered. The goal of this study was to compare the intrinsic image quality of synthesized 2D c-view and 2D FFDM images in terms of resolution, contrast, and noise.Two phantoms were utilized in this study: the American College of Radiology mammography accreditation phantom (ACR phantom) and a novel 3D printed anthropomorphic breast phantom. Both phantoms were imaged using a Hologic Selenia Dimensions 3D system. Analysis of the ACR phantom includes both visual inspection and objective automated analysis using in-house software. Analysis of the 3D anthropomorphic phantom includes visual assessment of resolution and Fourier analysis of the noise.Using ACR-defined scoring criteria for the ACR phantom, the FFDM images scored statistically higher than c-view according to both the average observer and automated scores. In addition, between 50% and 70% of c-view images failed to meet the nominal minimum ACR accreditation requirements-primarily due to fiber breaks. Software analysis demonstrated that c-view provided enhanced visualization of medium and large microcalcification objects; however, the benefits diminished for smaller high contrast objects and all low contrast objects. Visual analysis of the anthropomorphic phantom showed a measureable loss of resolution in the c-view image (11 lp/mm FFDM, 5 lp/mm c-view) and loss in detection of small microcalcification objects. Spectral analysis of the anthropomorphic phantom showed higher total noise magnitude in the FFDM image compared with c-view. Whereas the FFDM image contained approximately white noise texture, the c-view image exhibited marked noise reduction at midfrequency and high frequency with far less noise suppression at low frequencies resulting in a mottled noise appearance.Their analysis demonstrates many instances where the c-view image quality differs from FFDM. Compared to FFDM, c-view offers a better depiction of objects of certain size and contrast, but provides poorer overall resolution and noise properties. Based on these findings, the utilization of c-view images in the clinical setting requires careful consideration, especially if considering the discontinuation of FFDM imaging. Not explicitly explored in this study is how the combination of DBT + c-view performs relative to DBT + FFDM or FFDM alone.

Authors
Nelson, JS; Wells, JR; Baker, JA; Samei, E
MLA Citation
Nelson, JS, Wells, JR, Baker, JA, and Samei, E. "How does c-view image quality compare with conventional 2D FFDM?." Medical physics 43.5 (May 2016): 2538-.
PMID
27147364
Source
epmc
Published In
Medical physics
Volume
43
Issue
5
Publish Date
2016
Start Page
2538
DOI
10.1118/1.4947293

Finite-element modeling of compression and gravity on a population of breast phantoms for multimodality imaging simulation.

The authors are developing a series of computational breast phantoms based on breast CT data for imaging research. In this work, the authors develop a program that will allow a user to alter the phantoms to simulate the effect of gravity and compression of the breast (craniocaudal or mediolateral oblique) making the phantoms applicable to multimodality imaging.This application utilizes a template finite-element (FE) breast model that can be applied to their presegmented voxelized breast phantoms. The FE model is automatically fit to the geometry of a given breast phantom, and the material properties of each element are set based on the segmented voxels contained within the element. The loading and boundary conditions, which include gravity, are then assigned based on a user-defined position and compression. The effect of applying these loads to the breast is computed using a multistage contact analysis in FEBio, a freely available and well-validated FE software package specifically designed for biomedical applications. The resulting deformation of the breast is then applied to a boundary mesh representation of the phantom that can be used for simulating medical images. An efficient script performs the above actions seamlessly. The user only needs to specify which voxelized breast phantom to use, the compressed thickness, and orientation of the breast.The authors utilized their FE application to simulate compressed states of the breast indicative of mammography and tomosynthesis. Gravity and compression were simulated on example phantoms and used to generate mammograms in the craniocaudal or mediolateral oblique views. The simulated mammograms show a high degree of realism illustrating the utility of the FE method in simulating imaging data of repositioned and compressed breasts.The breast phantoms and the compression software can become a useful resource to the breast imaging research community. These phantoms can then be used to evaluate and compare imaging modalities that involve different positioning and compression of the breast.

Authors
Sturgeon, GM; Kiarashi, N; Lo, JY; Samei, E; Segars, WP
MLA Citation
Sturgeon, GM, Kiarashi, N, Lo, JY, Samei, E, and Segars, WP. "Finite-element modeling of compression and gravity on a population of breast phantoms for multimodality imaging simulation." Medical physics 43.5 (May 2016): 2207-.
PMID
27147333
Source
epmc
Published In
Medical physics
Volume
43
Issue
5
Publish Date
2016
Start Page
2207
DOI
10.1118/1.4945275

Convolution-based estimation of organ dose in tube current modulated CT.

Estimating organ dose for clinical patients requires accurate modeling of the patient anatomy and the dose field of the CT exam. The modeling of patient anatomy can be achieved using a library of representative computational phantoms (Samei et al 2014 Pediatr. Radiol. 44 460-7). The modeling of the dose field can be challenging for CT exams performed with a tube current modulation (TCM) technique. The purpose of this work was to effectively model the dose field for TCM exams using a convolution-based method. A framework was further proposed for prospective and retrospective organ dose estimation in clinical practice. The study included 60 adult patients (age range: 18-70 years, weight range: 60-180 kg). Patient-specific computational phantoms were generated based on patient CT image datasets. A previously validated Monte Carlo simulation program was used to model a clinical CT scanner (SOMATOM Definition Flash, Siemens Healthcare, Forchheim, Germany). A practical strategy was developed to achieve real-time organ dose estimation for a given clinical patient. CTDIvol-normalized organ dose coefficients ([Formula: see text]) under constant tube current were estimated and modeled as a function of patient size. Each clinical patient in the library was optimally matched to another computational phantom to obtain a representation of organ location/distribution. The patient organ distribution was convolved with a dose distribution profile to generate [Formula: see text] values that quantified the regional dose field for each organ. The organ dose was estimated by multiplying [Formula: see text] with the organ dose coefficients ([Formula: see text]). To validate the accuracy of this dose estimation technique, the organ dose of the original clinical patient was estimated using Monte Carlo program with TCM profiles explicitly modeled. The discrepancy between the estimated organ dose and dose simulated using TCM Monte Carlo program was quantified. We further compared the convolution-based organ dose estimation method with two other strategies with different approaches of quantifying the irradiation field. The proposed convolution-based estimation method showed good accuracy with the organ dose simulated using the TCM Monte Carlo simulation. The average percentage error (normalized by CTDIvol) was generally within 10% across all organs and modulation profiles, except for organs located in the pelvic and shoulder regions. This study developed an improved method that accurately quantifies the irradiation field under TCM scans. The results suggested that organ dose could be estimated in real-time both prospectively (with the localizer information only) and retrospectively (with acquired CT data).

Authors
Tian, X; Segars, WP; Dixon, RL; Samei, E
MLA Citation
Tian, X, Segars, WP, Dixon, RL, and Samei, E. "Convolution-based estimation of organ dose in tube current modulated CT." Physics in medicine and biology 61.10 (May 2016): 3935-3954.
PMID
27119974
Source
epmc
Published In
Physics in Medicine and Biology
Volume
61
Issue
10
Publish Date
2016
Start Page
3935
End Page
3954
DOI
10.1088/0031-9155/61/10/3935

Quantitative Features of Liver Lesions, Lung Nodules, and Renal Stones at Multi-Detector Row CT Examinations: Dependency on Radiation Dose and Reconstruction Algorithm.

To determine if radiation dose and reconstruction algorithm affect the computer-based extraction and analysis of quantitative imaging features in lung nodules, liver lesions, and renal stones at multi-detector row computed tomography (CT).Retrospective analysis of data from a prospective, multicenter, HIPAA-compliant, institutional review board-approved clinical trial was performed by extracting 23 quantitative imaging features (size, shape, attenuation, edge sharpness, pixel value distribution, and texture) of lesions on multi-detector row CT images of 20 adult patients (14 men, six women; mean age, 63 years; range, 38-72 years) referred for known or suspected focal liver lesions, lung nodules, or kidney stones. Data were acquired between September 2011 and April 2012. All multi-detector row CT scans were performed at two different radiation dose levels; images were reconstructed with filtered back projection, adaptive statistical iterative reconstruction, and model-based iterative reconstruction (MBIR) algorithms. A linear mixed-effects model was used to assess the effect of radiation dose and reconstruction algorithm on extracted features.Among the 23 imaging features assessed, radiation dose had a significant effect on five, three, and four of the features for liver lesions, lung nodules, and renal stones, respectively (P < .002 for all comparisons). Adaptive statistical iterative reconstruction had a significant effect on three, one, and one of the features for liver lesions, lung nodules, and renal stones, respectively (P < .002 for all comparisons). MBIR reconstruction had a significant effect on nine, 11, and 15 of the features for liver lesions, lung nodules, and renal stones, respectively (P < .002 for all comparisons). Of note, the measured size of lung nodules and renal stones with MBIR was significantly different than those for the other two algorithms (P < .002 for all comparisons). Although lesion texture was significantly affected by the reconstruction algorithm used (average of 3.33 features affected by MBIR throughout lesion types; P < .002, for all comparisons), no significant effect of the radiation dose setting was observed for all but one of the texture features (P = .002-.998).Radiation dose settings and reconstruction algorithms affect the extraction and analysis of quantitative imaging features in lesions at multi-detector row CT.

Authors
Solomon, J; Mileto, A; Nelson, RC; Roy Choudhury, K; Samei, E
MLA Citation
Solomon, J, Mileto, A, Nelson, RC, Roy Choudhury, K, and Samei, E. "Quantitative Features of Liver Lesions, Lung Nodules, and Renal Stones at Multi-Detector Row CT Examinations: Dependency on Radiation Dose and Reconstruction Algorithm." Radiology 279.1 (April 2016): 185-194.
PMID
26624973
Source
epmc
Published In
Radiology
Volume
279
Issue
1
Publish Date
2016
Start Page
185
End Page
194
DOI
10.1148/radiol.2015150892

A quantitative metrology for performance characterization of five breast tomosynthesis systems based on an anthropomorphic phantom.

In medical imaging systems, proper rendition of anatomy is essential in discerning normal tissue from disease. Currently, digital breast tomosynthesis (DBT) systems are evaluated using subjective evaluation of lesion visibility in uniform phantoms. This study involved the development of a new methodology to objectively measure the rendition of a 3D breast model by an anthropomorphic breast phantom, and its implementation on five clinical DBT systems of different makes and models.A 3D, patient-based breast phantom was fabricated based on XCAT breast models. This phantom was imaged on representative breast tomosynthesis systems. The ability of tomosynthesis systems to accurately reproduce the 3D structure of the breast was assessed by computational analysis of the resultant images in terms of three groups of indices: contrast index (CI), reflective of local difference between adipose and glandular material; adipose variability index (AVI), reflective of contributions of noise and artifacts within uniform adipose regions; and contrast detectability, which describes contrast against local background variability and is described by contrast variability index (CVI), coefficient of variation (COV), contrast to adipose variability index (CAVI), and contrast to noise ratio index (CNRI). The indices were obtained by comparing the image data to the gold standard 3D distribution of breast tissue in the model. Corresponding indices were measured within variable region of interest (ROI) sizes ranging from 10 to 37 mm. The characterization was performed on five tomosynthesis systems: Fuji Aspire Crystal, GE Essential, Hologic Dimension, IMS Giotto, and Siemens Inspiration, all evaluated at a fixed dose of 1.5 mGy average glandular dose, anonymized in random order from A to E.Results are provided as a function of ROI size. The systems ranked orders in terms of CI with values of 7.4%, 7.0%, 6.9%, 6.4%, and 5.2% for systems A-E, respectively. This system ranking was identical for CNRI. Both CI and CNRI were constant over ROI size. The ranking was similar for CVI. The COV also changed little with ROI size and was similar across systems. For 10 mm ROIs, the average system COV was 0.7, which reduced to 0.5 with 37 mm ROIs. Two systems (A and B) exhibited highest AVI values when measured in 10 mm ROIs. This, however, was ROI-size-dependent with the three other systems (C-E) yielding higher AVI values when measured with 37 mm ROIs. Two systems (B and E) showed inferior CAVI compared to others.The quality of rendition tracked with differences in image appearance across systems. The findings illustrate that the anthropomorphic phantom can be used as a basis to extract quantitative values of image attributes in DBT.

Authors
Ikejimba, L; Lo, JY; Chen, Y; Oberhofer, N; Kiarashi, N; Samei, E
MLA Citation
Ikejimba, L, Lo, JY, Chen, Y, Oberhofer, N, Kiarashi, N, and Samei, E. "A quantitative metrology for performance characterization of five breast tomosynthesis systems based on an anthropomorphic phantom." Medical physics 43.4 (April 2016): 1627-.
PMID
27036562
Source
epmc
Published In
Medical physics
Volume
43
Issue
4
Publish Date
2016
Start Page
1627
DOI
10.1118/1.4943373

Determination of contrast media administration to achieve a targeted contrast enhancement in computed tomography.

Contrast enhancement is a key component of computed tomography (CT) imaging and offers opportunities for optimization. The design and optimization of techniques, however, require orchestration with the scan parameters and, further, a methodology to relate contrast enhancement and injection function. We used such a methodology to develop a method, the analytical inverse method, to predict the required injection function to achieve a desired contrast enhancement in a given organ by incorporation of a physiologically based compartmental model. The method was evaluated across 32 different target contrast enhancement functions for aorta, kidney, stomach, small intestine, and liver. The results exhibited that the analytical inverse method offers accurate performance with error in the range of 10% deviation between the predicted and desired organ enhancement curves. However, this method is incapable of predicting the injection function based on the liver enhancement. The findings of this study can be useful in optimizing contrast medium injection function as well as scan timing to provide more consistency in the way contrast-enhanced CT examinations are performed. To our knowledge, this work is one of the first attempts to predict the contrast material injection function for a desired organ enhancement curve.

Authors
Sahbaee, P; Segars, PP; Marin, D; Nelson, R; Samei, E
MLA Citation
Sahbaee, P, Segars, PP, Marin, D, Nelson, R, and Samei, E. "Determination of contrast media administration to achieve a targeted contrast enhancement in computed tomography." Journal of medical imaging (Bellingham, Wash.) 3.1 (January 20, 2016): 013501-.
PMID
26835498
Source
epmc
Published In
Journal of medical imaging (Bellingham, Wash.)
Volume
3
Issue
1
Publish Date
2016
Start Page
013501
DOI
10.1117/1.jmi.3.1.013501

Design, fabrication, and implementation of voxel-based 3D printed textured phantoms for task-based image quality assessment in CT

© 2016 SPIE.In x-ray computed tomography (CT), task-based image quality studies are typically performed using uniform background phantoms with low-contrast signals. Such studies may have limited clinical relevancy for modern non-linear CT systems due to possible influence of background texture on image quality. The purpose of this study was to design and implement anatomically informed textured phantoms for task-based assessment of low-contrast detection. Liver volumes were segmented from 23 abdominal CT cases. The volumes were characterized in terms of texture features from gray-level co-occurrence and run-length matrices. Using a 3D clustered lumpy background (CLB) model, a fitting technique based on a genetic optimization algorithm was used to find the CLB parameters that were most reflective of the liver textures, accounting for CT system factors of spatial blurring and noise. With the modeled background texture as a guide, a cylinder phantom (165 mm in diameter and 30 mm height) was designed, containing 20 low-contrast spherical signals (6 mm in diameter at targeted contrast levels of ∼3.2, 5.2, 7.2, 10, and 14 HU, 4 repeats per signal). The phantom was voxelized and input into a commercial multi-material 3D printer (Object Connex 350), with custom software for voxel-based printing. Using principles of digital half-toning and dithering, the 3D printer was programmed to distribute two base materials (VeroWhite and TangoPlus, nominal voxel size of 42x84x30 microns) to achieve the targeted spatial distribution of x-ray attenuation properties. The phantom was used for task-based image quality assessment of a clinically available iterative reconstruction algorithm (Sinogram Affirmed Iterative Reconstruction, SAFIRE) using a channelized Hotelling observer paradigm. Images of the textured phantom and a corresponding uniform phantom were acquired at six dose levels and observer model performance was estimated for each condition (5 contrasts x 6 doses x 2 reconstructions x 2 backgrounds = 120 total conditions). Based on the observer model results, the dose reduction potential of SAFIRE was computed and compared between the uniform and textured phantom. The dose reduction potential of SAFIRE was found to be 23% based on the uniform phantom and 17% based on the textured phantom. This discrepancy demonstrates the need to consider background texture when assessing non-linear reconstruction algorithms.

Authors
Solomon, J; Ba, A; Diao, A; Lo, J; Bier, E; Bochud, F; Gehm, M; Samei, E
MLA Citation
Solomon, J, Ba, A, Diao, A, Lo, J, Bier, E, Bochud, F, Gehm, M, and Samei, E. "Design, fabrication, and implementation of voxel-based 3D printed textured phantoms for task-based image quality assessment in CT." January 1, 2016.
Source
scopus
Published In
Proceedings of SPIE
Volume
9783
Publish Date
2016
DOI
10.1117/12.2217463

Second generation anthropomorphic physical phantom for mammography and DBT: Incorporating voxelized 3D printing and inkjet printing of iodinated lesion inserts

© 2016 SPIE.Physical phantoms are needed for the evaluation and optimization of new digital breast tomosynthesis (DBT) systems. Previously, we developed an anthropomorphic phantom based on human subject breast CT data and fabricated using commercial 3D printing. We now present three key advancements: voxelized 3D printing, photopolymer material doping, and 2D inkjet printing of lesion inserts. First, we bypassed the printer's control software in order to print in voxelized form instead of conventional STL surfaces, thus improving resolution and allowing dithering to mix the two photopolymer materials into arbitrary proportions. We demonstrated ability to print details as small as 150μm, and dithering to combine VeroWhitePlus and TangoPlus in 10% increments. Second, to address the limited attenuation difference among commercial photopolymers, we evaluated a beta sample from Stratasys with increased TiO2 doping concentration up to 2.5%, which corresponded to 98% breast density. By spanning 36% to 98% breast density, this doubles our previous contrast. Third, using inkjet printers modified to print with iopamidol, we created 2D lesion patterns on paper that can be sandwiched into the phantom. Inkjet printing has advantages of being inexpensive and easy, and more contrast can be delivered through overprinting. Printing resolution was maintained at 210 μm horizontally and 330 μm vertically even after 10 overprints. Contrast increased linearly with overprinting at 0.7% per overprint. Together, these three new features provide the basis for creating a new anthropomorphic physical breast phantom with improved resolution and contrast, as well as the ability to insert 2D lesions for task-based assessment of performance.

Authors
Sikaria, D; Musinsky, S; Sturgeon, GM; Solomon, J; Diao, A; Gehm, ME; Samei, E; Glick, SJ; Lo, JY
MLA Citation
Sikaria, D, Musinsky, S, Sturgeon, GM, Solomon, J, Diao, A, Gehm, ME, Samei, E, Glick, SJ, and Lo, JY. "Second generation anthropomorphic physical phantom for mammography and DBT: Incorporating voxelized 3D printing and inkjet printing of iodinated lesion inserts." January 1, 2016.
Source
scopus
Published In
Proceedings of SPIE
Volume
9783
Publish Date
2016
DOI
10.1117/12.2217667

Coded aperture coherent scatter imaging for breast cancer detection: A Monte Carlo evaluation

© 2016 SPIE.It is known that conventional x-ray imaging provides a maximum contrast between cancerous and healthy fibroglandular breast tissues of 3% based on their linear x-ray attenuation coefficients at 17.5 keV, whereas coherent scatter signal provides a maximum contrast of 19% based on their differential coherent scatter cross sections. Therefore in order to exploit this potential contrast, we seek to evaluate the performance of a coded- aperture coherent scatter imaging system for breast cancer detection and investigate its accuracy using Monte Carlo simulations. In the simulations we modeled our experimental system, which consists of a raster-scanned pencil beam of x-rays, a bismuth-tin coded aperture mask comprised of a repeating slit pattern with 2-mm periodicity, and a linear-array of 128 detector pixels with 6.5-keV energy resolution. The breast tissue that was scanned comprised a 3-cm sample taken from a patient-based XCAT breast phantom containing a tomosynthesis- based realistic simulated lesion. The differential coherent scatter cross section was reconstructed at each pixel in the image using an iterative reconstruction algorithm. Each pixel in the reconstructed image was then classified as being either air or the type of breast tissue with which its normalized reconstructed differential coherent scatter cross section had the highest correlation coefficient. Comparison of the final tissue classification results with the ground truth image showed that the coded aperture imaging technique has a cancerous pixel detection sensitivity (correct identification of cancerous pixels), specificity (correctly ruling out healthy pixels as not being cancer) and accuracy of 92.4%, 91.9% and 92.0%, respectively. Our Monte Carlo evaluation of our experimental coded aperture coherent scatter imaging system shows that it is able to exploit the greater contrast available from coherently scattered x-rays to increase the accuracy of detecting cancerous regions within the breast.

Authors
Lakshmanan, MN; Morris, RE; Greenberg, JA; Samei, E; Kapadia, AJ
MLA Citation
Lakshmanan, MN, Morris, RE, Greenberg, JA, Samei, E, and Kapadia, AJ. "Coded aperture coherent scatter imaging for breast cancer detection: A Monte Carlo evaluation." January 1, 2016.
Source
scopus
Published In
Proceedings of SPIE
Volume
9783
Publish Date
2016
DOI
10.1117/12.2216482

Comparison of model and human observer performance in FFDM, DBT, and synthetic mammography

© 2016 SPIE.Reader studies are important in assessing breast imaging systems. The purpose of this work was to assess task-based performance of full field digital mammography (FFDM), digital breast tomosynthesis (DBT), and synthetic mammography (SM) using different phantom types, and to determine an accurate observer model for human readers. Images were acquired on a Hologic Selenia Dimensions system with a uniform and anthropomorphic phantom. A contrast detail insert of small, low-contrast disks was created using an inkjet printer with iodine-doped ink and inserted in the phantoms. The disks varied in diameter from 210 to 630 μm, and in contrast from 1.1% contrast to 2.2% in regular increments. Human and model observers performed a 4-alternative forced choice experiment. The models were a non-prewhitening matched filter with eye model (NPWE) and a channelized Hotelling observer with either Gabor channels (Gabor-CHO) or Laguerre-Gauss channels (LG-CHO). With the given phantoms, reader scores were higher in FFDM and DBT than SM. The structure in the phantom background had a bigger impact on outcome for DBT than for FFDM or SM. All three model observers showed good correlation with humans in the uniform background, with ρ between 0.89 and 0.93. However, in the structured background, only the CHOs had high correlation, with ρ=0.92 for Gabor-CHO, 0.90 for LG-CHO, and 0.77 for NPWE. Because results of any analysis can depend on the phantom structure, conclusions of modality performance may need to be taken in the context of an appropriate model observer and a realistic phantom.

Authors
Ikejimba, L; Glick, SJ; Samei, E; Lo, JY
MLA Citation
Ikejimba, L, Glick, SJ, Samei, E, and Lo, JY. "Comparison of model and human observer performance in FFDM, DBT, and synthetic mammography." January 1, 2016.
Source
scopus
Published In
Proceedings of SPIE
Volume
9783
Publish Date
2016
DOI
10.1117/12.2216858

A technique for multi-dimensional optimization of radiation dose, contrast dose, and image quality in CT imaging

© 2016 SPIE.The purpose of this study was to substantiate the interdependency of image quality, radiation dose, and contrast material dose in CT towards the patient-specific optimization of the imaging protocols. The study deployed two phantom platforms. First, a variable sized phantom containing an iodinated insert was imaged on a representative CT scanner at multiple CTDI values. The contrast and noise were measured from the reconstructed images for each phantom diameter. Linearly related to iodine-concentration, contrast to noise ratio (CNR), was calculated for different iodine-concentration levels. Second, the analysis was extended to a recently developed suit of 58 virtual human models (5D-XCAT) with added contrast dynamics. Emulating a contrast-enhanced abdominal image procedure and targeting a peak-enhancement in aorta, each XCAT phantom was "imaged" using a CT simulation platform. 3D surfaces for each patient/size established the relationship between iodine-concentration, dose, and CNR. The Sensitivity of Ratio (SR), defined as ratio of change in iodine-concentration versus dose to yield a constant change in CNR was calculated and compared at high and low radiation dose for both phantom platforms. The results show that sensitivity of CNR to iodine concentration is larger at high radiation dose (up to 73%). The SR results were highly affected by radiation dose metric; CTDI or organ dose. Furthermore, results showed that the presence of contrast material could have a profound impact on optimization results (up to 45%).

Authors
Sahbaee, P; Abadi, E; Sanders, J; Becchetti, M; Zhang, Y; Agasthya, G; Segars, P; Samei, E
MLA Citation
Sahbaee, P, Abadi, E, Sanders, J, Becchetti, M, Zhang, Y, Agasthya, G, Segars, P, and Samei, E. "A technique for multi-dimensional optimization of radiation dose, contrast dose, and image quality in CT imaging." January 1, 2016.
Source
scopus
Published In
Proceedings of SPIE
Volume
9783
Publish Date
2016
DOI
10.1117/12.2216516

Organ dose conversion coefficients for tube current modulated CT protocols for an adult population

© 2016 SPIE.In computed tomography (CT), patient-specific organ dose can be estimated using pre-calculated organ dose conversion coefficients (organ dose normalized by CTDIvol, h factor) database, taking into account patient size and scan coverage. The conversion coefficients have been previously estimated for routine body protocol classes, grouped by scan coverage, across an adult population for fixed tube current modulated CT. The coefficients, however, do not include the widely utilized tube current (mA) modulation scheme, which significantly impacts organ dose. This study aims to extend the h factors and the corresponding dose length product (DLP) to create effective dose conversion coefficients (k factor) database incorporating various tube current modulation strengths. Fifty-eight extended cardiac-torso (XCAT) phantoms were included in this study representing population anatomy variation in clinical practice. Four mA profiles, representing weak to strong mA dependency on body attenuation, were generated for each phantom and protocol class. A validated Monte Carlo program was used to simulate the organ dose. The organ dose and effective dose was further normalized by CTDIvol and DLP to derive the h factors and k factors, respectively. The h factors and k factors were summarized in an exponential regression model as a function of body size. Such a population-based mathematical model can provide a comprehensive organ dose estimation given body size and CTDIvol. The model was integrated into an iPhone app XCATdose version 2, enhancing the 1st version based upon fixed tube current modulation. With the organ dose calculator, physicists, physicians, and patients can conveniently estimate organ dose.

Authors
Fu, W; Tian, X; Sahbaee, P; Zhang, Y; Segars, WP; Samei, E
MLA Citation
Fu, W, Tian, X, Sahbaee, P, Zhang, Y, Segars, WP, and Samei, E. "Organ dose conversion coefficients for tube current modulated CT protocols for an adult population." January 1, 2016.
Source
scopus
Published In
Proceedings of SPIE
Volume
9783
Publish Date
2016
DOI
10.1117/12.2217271

An automated technique for estimating patient-specific regional imparted energy and dose in TCM CT exams

© 2016 SPIE.Currently computed tomography (CT) dosimetry relies on CT dose index (CTDI) and size specific dose estimates (SSDE). Organ dose is a better metric of radiation burden. However, organ dose estimation requires precise knowledge of organ locations. Regional imparted energy and dose can also be used to quantify radiation burden. Estimating the imparted energy from CT exams is beneficial in that it does not require precise estimates of the organ size or location. This work investigated an automated technique for retrospectively estimating the imparted energy from chest and abdominopelvic tube current modulated (TCM) CT exams. Monte Carlo simulations of chest and abdominopelvic TCM CT examinations across various tube potentials and TCM strengths were performed on 58 adult computational extended cardiac-torso (XCAT) phantoms to develop relationships between scanned mass and imparted energy normalized by dose length product (DLP). An automated algorithm for calculating the scanned patient volume was further developed using an open source mesh generation toolbox. The scanned patient volume was then used to estimate the scanned mass accounting for diverse density within the scan region. The scanned mass and DLP from the exam were used to estimate the imparted energy to the patient using the knowledgebase developed from the Monte Carlo simulations. Patientspecific imparted energy estimates were made from 20 chest and 20 abdominopelvic clinical CT exams. The average imparted energy was 274 ± 141 mJ and 681 ± 376 mJ for the chest and abdominopelvic exams, respectively. This method can be used to estimate the regional imparted energy and/or regional dose in chest and abdominopelvic TCM CT exams across clinical operations.

Authors
Sanders, JW; Tian, X; Segars, WP; Boone, J; Samei, E
MLA Citation
Sanders, JW, Tian, X, Segars, WP, Boone, J, and Samei, E. "An automated technique for estimating patient-specific regional imparted energy and dose in TCM CT exams." January 1, 2016.
Source
scopus
Published In
Proceedings of SPIE
Volume
9783
Publish Date
2016
DOI
10.1117/12.2216413

Estimation of breast dose saving potential using a breast positioning technique for organ-based tube current modulated CT

© 2016 SPIE.In thoracic CT, organ-based tube current modulation (OTCM) reduces breast dose by lowering the tube current in the 120° anterior dose reduction zone of patients. However, in practice the breasts usually expand to an angle larger than the dose reduction zone. This work aims to simulate a breast positioning technique (BPT) to constrain the breast tissue to within the dose reduction zone for OTCM and to evaluate the corresponding potential reduction in breast dose. Thirteen female anthropomorphic computational phantoms were studied (age range: 27-65 y.o., weight range: 52-105.8 kg). Each phantom was modeled in the supine position with and without application of the BPT. Attenuation-based tube current (ATCM, reference mA) was generated by a ray-tracing program, taking into account the patient attenuation change in the longitudinal and angular plane (CAREDose4D, Siemens Healthcare). OTCM was generated by reducing the mA to 20% between ± 60° anterior of the patient and increasing the mA in the remaining projections correspondingly (X-CARE, Siemens Healthcare) to maintain the mean tube current. Breast tissue dose was estimated using a validated Monte Carlo program for a commercial scanner (SOMATOM Definition Flash, Siemens Healthcare). Compared to standard tube current modulation, breast dose was significantly reduced using OTCM by 19.8±4.7%. With the BPT, breast dose was reduced by an additional 20.4±6.5% to 37.1±6.9%, using the same CTDIvol. BPT was more effective for phantoms simulating women with larger breasts with the average breast dose reduction of 30.2%, 39.2%, and 49.2% from OTCMBP to ATCM, using the same CTDIvol for phantoms with 0.5, 1.5, and 2.5 kg breasts, respectively. This study shows that a specially designed BPT improves the effectiveness of OTCM.

Authors
Fu, W; Tian, X; Sturgeon, G; Agasthya, G; Segars, WP; Goodsitt, MM; Kazerooni, EA; Samei, E
MLA Citation
Fu, W, Tian, X, Sturgeon, G, Agasthya, G, Segars, WP, Goodsitt, MM, Kazerooni, EA, and Samei, E. "Estimation of breast dose saving potential using a breast positioning technique for organ-based tube current modulated CT." January 1, 2016.
Source
scopus
Published In
Proceedings of SPIE
Volume
9783
Publish Date
2016
DOI
10.1117/12.2217239

Development of a Hausdorff distance based 3D quantification technique to evaluate the CT imaging system impact on depiction of lesion morphology

© 2016 SPIE.The purpose of this study was to develop a 3D quantification technique to assess the impact of imaging system on depiction of lesion morphology. Regional Hausdorff Distance (RHD) was computed from two 3D volumes: virtual mesh models of synthetic nodules or "virtual nodules" and CT images of physical nodules or "physical nodules". The method can be described in following steps. First, the synthetic nodule was inserted into anthropomorphic Kyoto thorax phantom and scanned in a Siemens scanner (Flash). Then, nodule was segmented from the image. Second, in order to match the orientation of the nodule, the digital models of the "virtual" and "physical" nodules were both geometrically translated to the origin. Then, the "physical" was gradually rotated at incremental 10 degrees. Third, the Hausdorff Distance was calculated from each pair of "virtual" and "physical" nodules. The minimum HD value represented the most matching pair. Finally, the 3D RHD map and the distribution of RHD were computed for the matched pair. The technique was scalarized using the FWHM of the RHD distribution. The analysis was conducted for various shapes (spherical, lobular, elliptical, and speculated) of nodules. The calculated FWHM values of RHD distribution for the 8-mm spherical, lobular, elliptical, and speculated "virtual" and "physical" nodules were 0.23, 0.42, 0.33, and 0.49, respectively.

Authors
Sahbaee, P; Robins, M; Solomon, J; Samei, E
MLA Citation
Sahbaee, P, Robins, M, Solomon, J, and Samei, E. "Development of a Hausdorff distance based 3D quantification technique to evaluate the CT imaging system impact on depiction of lesion morphology." January 1, 2016.
Source
scopus
Published In
Proceedings of SPIE
Volume
9783
Publish Date
2016
DOI
10.1117/12.2216503

Development and comparison of projection and image space 3D nodule insertion techniques

© 2016 SPIE.This study aimed to develop and compare two methods of inserting computerized virtual lesions into CT datasets. 24 physical (synthetic) nodules of three sizes and four morphologies were inserted into an anthropomorphic chest phantom (LUNGMAN, KYOTO KAGAKU). The phantom was scanned (Somatom Definition Flash, Siemens Healthcare) with and without nodules present, and images were reconstructed with filtered back projection and iterative reconstruction (SAFIRE) at 0.6 mm slice thickness using a standard thoracic CT protocol at multiple dose settings. Virtual 3D CAD models based on the physical nodules were virtually inserted (accounting for the system MTF) into the nodule-free CT data using two techniques. These techniques include projection-based and image-based insertion. Nodule volumes were estimated using a commercial segmentation tool (iNtuition, TeraRecon, Inc.). Differences were tested using paired t-tests and R2 goodness of fit between the virtually and physically inserted nodules. Both insertion techniques resulted in nodule volumes very similar to the real nodules (<3% difference) and in most cases the differences were not statistically significant. Also, R2 values were all <0.97 for both insertion techniques. These data imply that these techniques can confidently be used as a means of inserting virtual nodules in CT datasets. These techniques can be instrumental in building hybrid CT datasets composed of patient images with virtually inserted nodules.

Authors
Robins, M; Solomon, J; Sahbaee, P; Samei, E
MLA Citation
Robins, M, Solomon, J, Sahbaee, P, and Samei, E. "Development and comparison of projection and image space 3D nodule insertion techniques." January 1, 2016.
Source
scopus
Published In
Proceedings of SPIE
Volume
9783
Publish Date
2016
DOI
10.1117/12.2216930

Synthesized interstitial lung texture for use in anthropomorphic computational phantoms

© 2016 SPIE.A realistic model of the anatomical texture from the pulmonary interstitium was developed with the goal of extending the capability of anthropomorphic computational phantoms (e.g., XCAT, Duke University), allowing for more accurate image quality assessment. Contrast-enhanced, high dose, thorax images for a healthy patient from a clinical CT system (Discovery CT750HD, GE healthcare) with thin (0.625 mm) slices and filtered back- projection (FBP) were used to inform the model. The interstitium which gives rise to the texture was defined using 24 volumes of interest (VOIs). These VOIs were selected manually to avoid vasculature, bronchi, and bronchioles. A small scale Hessian-based line filter was applied to minimize the amount of partial-volumed supernumerary vessels and bronchioles within the VOIs. The texture in the VOIs was characterized using 8 Haralick and 13 gray-level run length features. A clustered lumpy background (CLB) model with added noise and blurring to match CT system was optimized to resemble the texture in the VOIs using a genetic algorithm with the Mahalanobis distance as a similarity metric between the texture features. The most similar CLB model was then used to generate the interstitial texture to fill the lung. The optimization improved the similarity by 45%. This will substantially enhance the capabilities of anthropomorphic computational phantoms, allowing for more realistic CT simulations.

Authors
Becchetti, MF; Solomon, JB; Segars, WP; Samei, E
MLA Citation
Becchetti, MF, Solomon, JB, Segars, WP, and Samei, E. "Synthesized interstitial lung texture for use in anthropomorphic computational phantoms." January 1, 2016.
Source
scopus
Published In
Proceedings of SPIE
Volume
9783
Publish Date
2016
DOI
10.1117/12.2217135

Effects of automatic tube potential selection on radiation dose index, image quality, and lesion detectability in pediatric abdominopelvic CT and CTA: a phantom study.

To assess the effect of automatic tube potential selection (ATPS) on radiation dose, image quality, and lesion detectability in paediatric abdominopelvic CT and CT angiography (CTA).A paediatric modular phantom with contrast inserts was examined with routine pitch (1.4) and high pitch (3.0) using a standard abdominopelvic protocol with fixed 120 kVp, and ATPS with variable kVp in non-contrast, contrast-enhanced, and CTA mode. The volume CT dose index (CTDIvol), contrast-to-noise ratio (CNR) and lesion detectability index (d') were compared between the standard protocol and ATPS examinations.CTDIvol was reduced in all routine pitch ATPS examinations, with dose reductions of 27-52 % in CTA mode (P < 0.0001), 15-33 % in contrast-enhanced mode (P = 0.0003) and 8-14 % in non-contrast mode (P = 0.03). Iodine and soft tissue insert CNR and d' were improved or maintained in all ATPS examinations. kVp and dose were reduced in 25 % of high pitch ATPS examinations and in none of the full phantom examinations obtained after a single full phantom localizer.ATPS reduces radiation dose while maintaining image quality and lesion detectability in routine pitch paediatric abdominopelvic CT and CTA, but technical factors such as pitch and imaging range must be considered to optimize ATPS benefits.ATPS automatically individualizes CT scan technique for each patient. ATPS lowers radiation dose in routine pitch pediatric abdominopelvic CT and CTA. There is no loss of image quality or lesion detectability with ATPS. Pitch and scan range impact the effectiveness of ATPS dose reduction.

Authors
Brinkley, MF; Ramirez-Giraldo, JC; Samei, E; Frush, DJ; Choudhury, KR; Wilson, JM; Christianson, OI; Frush, DP
MLA Citation
Brinkley, MF, Ramirez-Giraldo, JC, Samei, E, Frush, DJ, Choudhury, KR, Wilson, JM, Christianson, OI, and Frush, DP. "Effects of automatic tube potential selection on radiation dose index, image quality, and lesion detectability in pediatric abdominopelvic CT and CTA: a phantom study." European radiology 26.1 (January 2016): 157-166.
PMID
25991484
Source
epmc
Published In
European Radiology
Volume
26
Issue
1
Publish Date
2016
Start Page
157
End Page
166
DOI
10.1007/s00330-015-3817-x

Cutting to the Chase: With So Much Physics "Stuff," What Do Radiologists Really Need to Know?

Authors
Samei, E
MLA Citation
Samei, E. "Cutting to the Chase: With So Much Physics "Stuff," What Do Radiologists Really Need to Know?." AJR. American journal of roentgenology 206.1 (January 2016): W9-.
PMID
26700368
Source
epmc
Published In
AJR. American journal of roentgenology
Volume
206
Issue
1
Publish Date
2016
Start Page
W9
DOI
10.2214/ajr.15.15223

Population of 224 realistic human subject-based computational breast phantoms.

To create a database of highly realistic and anatomically variable 3D virtual breast phantoms based on dedicated breast computed tomography (bCT) data.A tissue classification and segmentation algorithm was used to create realistic and detailed 3D computational breast phantoms based on 230 + dedicated bCT datasets from normal human subjects. The breast volume was identified using a coarse three-class fuzzy C-means segmentation algorithm which accounted for and removed motion blur at the breast periphery. Noise in the bCT data was reduced through application of a postreconstruction 3D bilateral filter. A 3D adipose nonuniformity (bias field) correction was then applied followed by glandular segmentation using a 3D bias-corrected fuzzy C-means algorithm. Multiple tissue classes were defined including skin, adipose, and several fractional glandular densities. Following segmentation, a skin mask was produced which preserved the interdigitated skin, adipose, and glandular boundaries of the skin interior. Finally, surface modeling was used to produce digital phantoms with methods complementary to the XCAT suite of digital human phantoms.After rejecting some datasets due to artifacts, 224 virtual breast phantoms were created which emulate the complex breast parenchyma of actual human subjects. The volume breast density (with skin) ranged from 5.5% to 66.3% with a mean value of 25.3% ± 13.2%. Breast volumes ranged from 25.0 to 2099.6 ml with a mean value of 716.3 ± 386.5 ml. Three breast phantoms were selected for imaging with digital compression (using finite element modeling) and simple ray-tracing, and the results show promise in their potential to produce realistic simulated mammograms.This work provides a new population of 224 breast phantoms based on in vivo bCT data for imaging research. Compared to previous studies based on only a few prototype cases, this dataset provides a rich source of new cases spanning a wide range of breast types, volumes, densities, and parenchymal patterns.

Authors
Erickson, DW; Wells, JR; Sturgeon, GM; Samei, E; Dobbins, JT; Segars, WP; Lo, JY
MLA Citation
Erickson, DW, Wells, JR, Sturgeon, GM, Samei, E, Dobbins, JT, Segars, WP, and Lo, JY. "Population of 224 realistic human subject-based computational breast phantoms." Medical physics 43.1 (January 2016): 23-.
PMID
26745896
Source
epmc
Published In
Medical physics
Volume
43
Issue
1
Publish Date
2016
Start Page
23
DOI
10.1118/1.4937597

Accurate assessment and prediction of noise in clinical CT images.

The objectives of this study were (a) to devise a technique for measuring quantum noise in clinical body computed tomography (CT) images and (b) to develop a model for predicting that noise with high accuracy.The study included 83 clinical image sets at two dose levels (clinical and 50% reduced dose levels). The quantum noise in clinical images was measured by subtracting sequential slices and filtering out edges. Noise was then measured in the resultant uniform area. The noise measurement technique was validated using 17 clinical image cases and a turkey phantom. With a validated method to measure noise in clinical images, this noise was predicted by establishing the correlation between water-equivalent diameter (Dw) and noise in a variable-sized phantom and ascribing a noise level to the patient based on Dw estimated from CT image. The accuracy of this prediction model was validated using 66 clinical image sets.The error in noise measurement was within 1.5 HU across two reconstruction algorithms. In terms of noise prediction, across the 83 clinical image sets, the average discrepancies between predicted and measured noise were 6.9% and 6.6% for adaptive statistical iterative reconstruction and filtered back projection reconstruction, respectively.This study proposed a practically applicable method to assess quantum noise in clinical images. The image-based measurement technique enables automatic quality control monitoring of image noise in clinical practice. Further, a phantom-based model can accurately predict quantum noise level in patient images. The prediction model can be used to quantitatively optimize individual protocol to achieve targeted noise level in clinical images.

Authors
Tian, X; Samei, E
MLA Citation
Tian, X, and Samei, E. "Accurate assessment and prediction of noise in clinical CT images." Medical physics 43.1 (January 2016): 475-.
PMID
26745940
Source
epmc
Published In
Medical physics
Volume
43
Issue
1
Publish Date
2016
Start Page
475
DOI
10.1118/1.4938588

Design and implementation of coded aperture coherent scatter spectral imaging of cancerous and healthy breast tissue samples.

A scatter imaging technique for the differentiation of cancerous and healthy breast tissue in a heterogeneous sample is introduced in this work. Such a technique has potential utility in intraoperative margin assessment during lumpectomy procedures. In this work, we investigate the feasibility of the imaging method for tumor classification using Monte Carlo simulations and physical experiments. The coded aperture coherent scatter spectral imaging technique was used to reconstruct three-dimensional (3-D) images of breast tissue samples acquired through a single-position snapshot acquisition, without rotation as is required in coherent scatter computed tomography. We perform a quantitative assessment of the accuracy of the cancerous voxel classification using Monte Carlo simulations of the imaging system; describe our experimental implementation of coded aperture scatter imaging; show the reconstructed images of the breast tissue samples; and present segmentations of the 3-D images in order to identify the cancerous and healthy tissue in the samples. From the Monte Carlo simulations, we find that coded aperture scatter imaging is able to reconstruct images of the samples and identify the distribution of cancerous and healthy tissues (i.e., fibroglandular, adipose, or a mix of the two) inside them with a cancerous voxel identification sensitivity, specificity, and accuracy of 92.4%, 91.9%, and 92.0%, respectively. From the experimental results, we find that the technique is able to identify cancerous and healthy tissue samples and reconstruct differential coherent scatter cross sections that are highly correlated with those measured by other groups using x-ray diffraction. Coded aperture scatter imaging has the potential to provide scatter images that automatically differentiate cancerous and healthy tissue inside samples within a time on the order of a minute per slice.

Authors
Lakshmanan, MN; Greenberg, JA; Samei, E; Kapadia, AJ
MLA Citation
Lakshmanan, MN, Greenberg, JA, Samei, E, and Kapadia, AJ. "Design and implementation of coded aperture coherent scatter spectral imaging of cancerous and healthy breast tissue samples." Journal of medical imaging (Bellingham, Wash.) 3.1 (January 2016): 013505-.
PMID
26962543
Source
epmc
Published In
Journal of medical imaging (Bellingham, Wash.)
Volume
3
Issue
1
Publish Date
2016
Start Page
013505
DOI
10.1117/1.jmi.3.1.013505

Evaluation of Low-Contrast Detectability of Iterative Reconstruction across Multiple Institutions, CT Scanner Manufacturers, and Radiation Exposure Levels.

To compare image resolution from iterative reconstruction with resolution from filtered back projection for low-contrast objects on phantom computed tomographic (CT) images across vendors and exposure levels.Randomized repeat scans of an American College of Radiology CT accreditation phantom (module 2, low contrast) were performed for multiple radiation exposures, vendors, and vendor iterative reconstruction algorithms. Eleven volunteers were presented with 900 images by using a custom-designed graphical user interface to perform a task created specifically for this reader study. Results were analyzed by using statistical graphics and analysis of variance.Across three vendors (blinded as A, B, and C) and across three exposure levels, the mean correct classification rate was higher for iterative reconstruction than filtered back projection (P < .01): 87.4% iterative reconstruction and 81.3% filtered back projection at 20 mGy, 70.3% iterative reconstruction and 63.9% filtered back projection at 12 mGy, and 61.0% iterative reconstruction and 56.4% filtered back projection at 7.2 mGy. There was a significant difference in mean correct classification rate between vendor B and the other two vendors. Across all exposure levels, images obtained by using vendor B's scanner outperformed the other vendors, with a mean correct classification rate of 74.4%, while the mean correct classification rate for vendors A and C was 68.1% and 68.3%, respectively. Across all readers, the mean correct classification rate for iterative reconstruction (73.0%) was higher compared with the mean correct classification rate for filtered back projection (67.0%).The potential exists to reduce radiation dose without compromising low-contrast detectability by using iterative reconstruction instead of filtered back projection. There is substantial variability across vendor reconstruction algorithms.

Authors
Saiprasad, G; Filliben, J; Peskin, A; Siegel, E; Chen, J; Trimble, C; Yang, Z; Christianson, O; Samei, E; Krupinski, E; Dima, A
MLA Citation
Saiprasad, G, Filliben, J, Peskin, A, Siegel, E, Chen, J, Trimble, C, Yang, Z, Christianson, O, Samei, E, Krupinski, E, and Dima, A. "Evaluation of Low-Contrast Detectability of Iterative Reconstruction across Multiple Institutions, CT Scanner Manufacturers, and Radiation Exposure Levels." Radiology 277.1 (October 2015): 124-133.
PMID
25989480
Source
epmc
Published In
Radiology
Volume
277
Issue
1
Publish Date
2015
Start Page
124
End Page
133
DOI
10.1148/radiol.2015141260

Monte Carlo reference data sets for imaging research: Executive summary of the report of AAPM Research Committee Task Group 195.

The use of Monte Carlo simulations in diagnostic medical imaging research is widespread due to its flexibility and ability to estimate quantities that are challenging to measure empirically. However, any new Monte Carlo simulation code needs to be validated before it can be used reliably. The type and degree of validation required depends on the goals of the research project, but, typically, such validation involves either comparison of simulation results to physical measurements or to previously published results obtained with established Monte Carlo codes. The former is complicated due to nuances of experimental conditions and uncertainty, while the latter is challenging due to typical graphical presentation and lack of simulation details in previous publications. In addition, entering the field of Monte Carlo simulations in general involves a steep learning curve. It is not a simple task to learn how to program and interpret a Monte Carlo simulation, even when using one of the publicly available code packages. This Task Group report provides a common reference for benchmarking Monte Carlo simulations across a range of Monte Carlo codes and simulation scenarios. In the report, all simulation conditions are provided for six different Monte Carlo simulation cases that involve common x-ray based imaging research areas. The results obtained for the six cases using four publicly available Monte Carlo software packages are included in tabular form. In addition to a full description of all simulation conditions and results, a discussion and comparison of results among the Monte Carlo packages and the lessons learned during the compilation of these results are included. This abridged version of the report includes only an introductory description of the six cases and a brief example of the results of one of the cases. This work provides an investigator the necessary information to benchmark his/her Monte Carlo simulation software against the reference cases included here before performing his/her own novel research. In addition, an investigator entering the field of Monte Carlo simulations can use these descriptions and results as a self-teaching tool to ensure that he/she is able to perform a specific simulation correctly. Finally, educators can assign these cases as learning projects as part of course objectives or training programs.

Authors
Sechopoulos, I; Ali, ESM; Badal, A; Badano, A; Boone, JM; Kyprianou, IS; Mainegra-Hing, E; McMillan, KL; McNitt-Gray, MF; Rogers, DWO; Samei, E; Turner, AC
MLA Citation
Sechopoulos, I, Ali, ESM, Badal, A, Badano, A, Boone, JM, Kyprianou, IS, Mainegra-Hing, E, McMillan, KL, McNitt-Gray, MF, Rogers, DWO, Samei, E, and Turner, AC. "Monte Carlo reference data sets for imaging research: Executive summary of the report of AAPM Research Committee Task Group 195." Medical physics 42.10 (October 2015): 5679-5691.
PMID
26429242
Source
epmc
Published In
Medical physics
Volume
42
Issue
10
Publish Date
2015
Start Page
5679
End Page
5691
DOI
10.1118/1.4928676

Volumetric x-ray coherent scatter imaging of cancer in resected breast tissue: a Monte Carlo study using virtual anthropomorphic phantoms.

Breast cancer patients undergoing surgery often choose to have a breast conserving surgery (BCS) instead of mastectomy for removal of only the breast tumor. If post-surgical analysis such as histological assessment of the resected tumor reveals insufficient healthy tissue margins around the cancerous tumor, the patient must undergo another surgery to remove the missed tumor tissue. Such re-excisions are reported to occur in 20%-70% of BCS patients. A real-time surgical margin assessment technique that is fast and consistently accurate could greatly reduce the number of re-excisions performed in BCS. We describe here a tumor margin assessment method based on x-ray coherent scatter computed tomography (CSCT) imaging and demonstrate its utility in surgical margin assessment using Monte Carlo simulations. A CSCT system was simulated in GEANT4 and used to simulate two virtual anthropomorphic CSCT scans of phantoms resembling surgically resected tissue. The resulting images were volume-rendered and found to distinguish cancerous tumors embedded in complex distributions of adipose and fibroglandular breast tissue (as is expected in the breast). The images exhibited sufficient spatial and spectral (i.e. momentum transfer) resolution to classify the tissue in any given voxel as healthy or cancerous. ROC analysis of the classification accuracy revealed an area under the curve of up to 0.97. These results indicate that coherent scatter imaging is promising as a possible fast and accurate surgical margin assessment technique.

Authors
Lakshmanan, MN; Harrawood, BP; Samei, E; Kapadia, AJ
MLA Citation
Lakshmanan, MN, Harrawood, BP, Samei, E, and Kapadia, AJ. "Volumetric x-ray coherent scatter imaging of cancer in resected breast tissue: a Monte Carlo study using virtual anthropomorphic phantoms." Physics in medicine and biology 60.16 (August 3, 2015): 6355-6370.
PMID
26237265
Source
epmc
Published In
Physics in Medicine and Biology
Volume
60
Issue
16
Publish Date
2015
Start Page
6355
End Page
6370
DOI
10.1088/0031-9155/60/16/6355

Characteristic image quality of a third generation dual-source MDCT scanner: Noise, resolution, and detectability.

The purpose of this work was to assess the inherent image quality characteristics of a new multidetector computed tomography system in terms of noise, resolution, and detectability index as a function of image acquisition and reconstruction for a range of clinically relevant settings.A multisized image quality phantom (37, 30, 23, 18.5, and 12 cm physical diameter) was imaged on a SOMATOM Force scanner (Siemens Medical Solutions) under variable dose, kVp, and tube current modulation settings. Images were reconstructed with filtered back projection (FBP) and with advanced modeled iterative reconstruction (ADMIRE) with iterative strengths of 3, 4, and 5. Image quality was assessed in terms of the noise power spectrum (NPS), task transfer function (TTF), and detectability index for a range of detection tasks (contrasts of approximately 45, 90, 300, -900, and 1000 HU, and 2-20 mm diameter) based on a non-prewhitening matched filter model observer with eye filter.Image noise magnitude decreased with decreasing phantom size, increasing dose, and increasing ADMIRE strength, offering up to 64% noise reduction relative to FBP. Noise texture in terms of the NPS was similar between FBP and ADMIRE (<5% shift in peak frequency). The resolution, based on the TTF, improved with increased ADMIRE strength by an average of 15% in the TTF 50% frequency for ADMIRE-5. The detectability index increased with increasing dose and ADMIRE strength by an average of 55%, 90%, and 163% for ADMIRE 3, 4, and 5, respectively. Assessing the impact of mA modulation for a fixed average dose over the length of the phantom, detectability was up to 49% lower in smaller phantom sections and up to 26% higher in larger phantom sections for the modulated scan compared to a fixed tube current scan. Overall, the detectability exhibited less variability with phantom size for modulated scans compared to fixed tube current scans.Image quality increased with increasing dose and decreasing phantom size. The CT system exhibited nonlinear noise and resolution properties, especially at very low-doses, large phantom sizes, and for low-contrast objects. Objective image quality metrics generally increased with increasing dose and ADMIRE strength, and with decreasing phantom size. The ADMIRE algorithm could offer comparable image quality at reduced doses or improved image quality at the same dose. The use of tube current modulation resulted in more consistent image quality with changing phantom size.

Authors
Solomon, J; Wilson, J; Samei, E
MLA Citation
Solomon, J, Wilson, J, and Samei, E. "Characteristic image quality of a third generation dual-source MDCT scanner: Noise, resolution, and detectability." Medical physics 42.8 (August 2015): 4941-4953.
PMID
26233220
Source
epmc
Published In
Medical physics
Volume
42
Issue
8
Publish Date
2015
Start Page
4941
End Page
4953
DOI
10.1118/1.4923172

The development of a population of 4D pediatric XCAT phantoms for imaging research and optimization.

We previously developed a set of highly detailed 4D reference pediatric extended cardiac-torso (XCAT) phantoms at ages of newborn, 1, 5, 10, and 15 yr with organ and tissue masses matched to ICRP Publication 89 values. In this work, we extended this reference set to a series of 64 pediatric phantoms of varying age and height and body mass percentiles representative of the public at large. The models will provide a library of pediatric phantoms for optimizing pediatric imaging protocols.High resolution positron emission tomography-computed tomography data obtained from the Duke University database were reviewed by a practicing experienced radiologist for anatomic regularity. The CT portion of the data was then segmented with manual and semiautomatic methods to form a target model defined using nonuniform rational B-spline surfaces. A multichannel large deformation diffeomorphic metric mapping algorithm was used to calculate the transform from the best age matching pediatric XCAT reference phantom to the patient target. The transform was used to complete the target, filling in the nonsegmented structures and defining models for the cardiac and respiratory motions. The complete phantoms, consisting of thousands of structures, were then manually inspected for anatomical accuracy. The mass for each major tissue was calculated and compared to linearly interpolated ICRP values for different ages.Sixty four new pediatric phantoms were created in this manner. Each model contains the same level of detail as the original XCAT reference phantoms and also includes parameterized models for the cardiac and respiratory motions. For the phantoms that were 10 yr old and younger, we included both sets of reproductive organs. This gave them the capability to simulate both male and female anatomy. With this, the population can be expanded to 92. Wide anatomical variation was clearly seen amongst the phantom models, both in organ shape and size, even for models of the same age and sex. The phantoms can be combined with existing simulation packages to generate realistic pediatric imaging data from different modalities.This work provides a large cohort of highly detailed pediatric phantoms with 4D capabilities of varying age, height, and body mass. The population of phantoms will provide a vital tool with which to optimize 3D and 4D pediatric imaging devices and techniques in terms of image quality and radiation-absorbed dose.

Authors
Segars, WP; Norris, H; Sturgeon, GM; Zhang, Y; Bond, J; Minhas, A; Tward, DJ; Ratnanather, JT; Miller, MI; Frush, D; Samei, E
MLA Citation
Segars, WP, Norris, H, Sturgeon, GM, Zhang, Y, Bond, J, Minhas, A, Tward, DJ, Ratnanather, JT, Miller, MI, Frush, D, and Samei, E. "The development of a population of 4D pediatric XCAT phantoms for imaging research and optimization." Medical physics 42.8 (August 2015): 4719-4726.
PMID
26233199
Source
epmc
Published In
Medical physics
Volume
42
Issue
8
Publish Date
2015
Start Page
4719
End Page
4726
DOI
10.1118/1.4926847

A Case for Wide-Angle Breast Tomosynthesis.

Conventional mammography is largely limited by superimposed anatomy. Digital breast tomosynthesis (DBT) and computed tomography (CT) alleviate this limitation but with added out-of-plane artifacts or limited chest wall coverage. This article presents a wide-angle breast tomosynthesis (WBT), aimed to provide a practical solution to these limitations, and offers an initial study of its utility in comparison with DBT and CT using a singular evaluation platform.Using an anthropomorphic virtual breast phantom, a Monte Carlo code modeled a breast imaging system for three modalities of DBT, WBT, and breast CT (44°, 99°, and 198° total angle range, respectively) at four breast compression levels, all at a constant mean glandular dose level of 1.5 mGy. Reconstructed volumes were generated using iterative reconstruction methods. Lesion detectability was estimated using contrast-to-noise ratio and a channelized Hotelling observer model in terms of the area under the receiver operating characteristic (AUC).Results showed improved detection with increased angular span and compression. The estimated AUCs for WBT were similar to that of CT. Comparative performance averaged over all thicknesses between CT and WBT was 4.3 ± 3.0%, whereas that between WBT and DBT was 5.6 ± 1.0%. At compression levels reflective of the modality (7-, 5-, and 4-cm thickness for CT, WBT, and DBT, respectively), WBT yielded an AUC comparable to CT (performance difference of 1.2%) but superior to DBT (performance difference of 5.5%).The proposed imaging modality showed significant advantages over conventional DBT. WBT exhibited superior imaging performance over DBT at lower compression levels, highlighting further potential for reduced breast compression.

Authors
Samei, E; Thompson, J; Richard, S; Bowsher, J
MLA Citation
Samei, E, Thompson, J, Richard, S, and Bowsher, J. "A Case for Wide-Angle Breast Tomosynthesis." Academic radiology 22.7 (July 2015): 860-869.
PMID
25920335
Source
epmc
Published In
Academic Radiology
Volume
22
Issue
7
Publish Date
2015
Start Page
860
End Page
869
DOI
10.1016/j.acra.2015.02.015

Automated Technique to Measure Noise in Clinical CT Examinations.

OBJECTIVE: The purpose of this study was to develop and validate an automated method to measure noise in clinical CT examinations. MATERIALS AND METHODS: An automated algorithm was developed to measure noise in CT images. To assess its validity, the global noise level was compared with image noise measured using an image subtraction technique in an anthropomorphic phantom. The global noise level was further compared with image noise values from clinical patient CT images obtained by an observer study. Finally, the clinical utility of the global noise level was shown by assessing variability of image noise across scanner models for abdominopelvic CT examinations performed in 2358 patients. RESULTS: The global noise level agreed well with the phantom-based and clinical image-based noise measurements, with an average difference of 3.4% and 4.7% from each of these measures, respectively. No significant difference was detected between the global noise level and the validation dataset in either case. It further indicated differences across scanners, with the median global noise level varying significantly between different scanner models (15-35%). CONCLUSION: The global noise level provides an accurate, robust, and automated method to measure CT noise in clinical examinations for quality assurance programs. The significant difference in noise across scanner models indicates the unexploited potential to efficiently assess and subsequently improve protocol consistency. Combined with other automated characterization of imaging performance (e.g., dose monitoring), the global noise level may offer a promising platform for the standardization and optimization of CT protocols.

Authors
Christianson, O; Winslow, J; Frush, DP; Samei, E
MLA Citation
Christianson, O, Winslow, J, Frush, DP, and Samei, E. "Automated Technique to Measure Noise in Clinical CT Examinations." AJR. American journal of roentgenology 205.1 (July 2015): W93-W99.
PMID
26102424
Source
epmc
Published In
AJR. American journal of roentgenology
Volume
205
Issue
1
Publish Date
2015
Start Page
W93
End Page
W99
DOI
10.2214/ajr.14.13613

Development of realistic physical breast phantoms matched to virtual breast phantoms based on human subject data.

Physical phantoms are essential for the development, optimization, and evaluation of x-ray breast imaging systems. Recognizing the major effect of anatomy on image quality and clinical performance, such phantoms should ideally reflect the three-dimensional structure of the human breast. Currently, there is no commercially available three-dimensional physical breast phantom that is anthropomorphic. The authors present the development of a new suite of physical breast phantoms based on human data.The phantoms were designed to match the extended cardiac-torso virtual breast phantoms that were based on dedicated breast computed tomography images of human subjects. The phantoms were fabricated by high-resolution multimaterial additive manufacturing (3D printing) technology. The glandular equivalency of the photopolymer materials was measured relative to breast tissue-equivalent plastic materials. Based on the current state-of-the-art in the technology and available materials, two variations were fabricated. The first was a dual-material phantom, the Doublet. Fibroglandular tissue and skin were represented by the most radiographically dense material available; adipose tissue was represented by the least radiographically dense material. The second variation, the Singlet, was fabricated with a single material to represent fibroglandular tissue and skin. It was subsequently filled with adipose-equivalent materials including oil, beeswax, and permanent urethane-based polymer. Simulated microcalcification clusters were further included in the phantoms via crushed eggshells. The phantoms were imaged and characterized visually and quantitatively.The mammographic projections and tomosynthesis reconstructed images of the fabricated phantoms yielded realistic breast background. The mammograms of the phantoms demonstrated close correlation with simulated mammographic projection images of the corresponding virtual phantoms. Furthermore, power-law descriptions of the phantom images were in general agreement with real human images. The Singlet approach offered more realistic contrast as compared to the Doublet approach, but at the expense of air bubbles and air pockets that formed during the filling process.The presented physical breast phantoms and their matching virtual breast phantoms offer realistic breast anatomy, patient variability, and ease of use, making them a potential candidate for performing both system quality control testing and virtual clinical trials.

Authors
Kiarashi, N; Nolte, AC; Sturgeon, GM; Segars, WP; Ghate, SV; Nolte, LW; Samei, E; Lo, JY
MLA Citation
Kiarashi, N, Nolte, AC, Sturgeon, GM, Segars, WP, Ghate, SV, Nolte, LW, Samei, E, and Lo, JY. "Development of realistic physical breast phantoms matched to virtual breast phantoms based on human subject data." Medical physics 42.7 (July 2015): 4116-4126.
PMID
26133612
Source
epmc
Published In
Medical physics
Volume
42
Issue
7
Publish Date
2015
Start Page
4116
End Page
4126
DOI
10.1118/1.4919771

An Improved Index of Image Quality for Task-based Performance of CT Iterative Reconstruction across Three Commercial Implementations.

PURPOSE: To develop and validate a metric of computed tomographic (CT) image quality that incorporates the noise texture and resolution properties of an image. MATERIALS AND METHODS: Images of the American College of Radiology CT quality assurance phantom were acquired by using three commercial CT systems at seven dose levels with filtered back projection (FBP) and iterative reconstruction (IR). Image quality was characterized by the contrast-to-noise ratio (CNR) and a detectability index (d') that incorporated noise texture and spatial resolution. The measured CNR and d' were compared with a corresponding observer study by using the Spearman rank correlation coefficient to determine how well each metric reflects the ability of an observer to detect subtle lesions. Statistical significance of the correlation between each metric and observer performance was determined by using a Student t distribution; P values less than .05 indicated a significant correlation. Additionally, each metric was used to estimate the dose reduction potential of IR algorithms while maintaining image quality. RESULTS: Across all dose levels, scanner models, and reconstruction algorithms, the d' correlated strongly with observer performance in the corresponding observer study (ρ = 0.95; P < .001), whereas the CNR correlated weakly with observer performance (ρ = 0.31; P = .21). Furthermore, the d' showed that the dose-reduction capabilities differed between clinical implementations (range, 12%-35%) and were less than those predicted from the CNR (range, 50%-54%). CONCLUSION: The strong correlation between the observer performance and the d' indicates that the d' is superior to the CNR for the evaluation of CT image quality. Moreover, the results of this study indicate that the d' improves less than the CNR with the use of IR, which indicates less potential for IR dose reduction than previously thought.

Authors
Christianson, O; Chen, JJS; Yang, Z; Saiprasad, G; Dima, A; Filliben, JJ; Peskin, A; Trimble, C; Siegel, EL; Samei, E
MLA Citation
Christianson, O, Chen, JJS, Yang, Z, Saiprasad, G, Dima, A, Filliben, JJ, Peskin, A, Trimble, C, Siegel, EL, and Samei, E. "An Improved Index of Image Quality for Task-based Performance of CT Iterative Reconstruction across Three Commercial Implementations." Radiology 275.3 (June 2015): 725-734.
PMID
25686365
Source
epmc
Published In
Radiology
Volume
275
Issue
3
Publish Date
2015
Start Page
725
End Page
734
DOI
10.1148/radiol.15132091

Diagnostic Performance of an Advanced Modeled Iterative Reconstruction Algorithm for Low-Contrast Detectability with a Third-Generation Dual-Source Multidetector CT Scanner: Potential for Radiation Dose Reduction in a Multireader Study.

PURPOSE: To assess the effect of radiation dose reduction on low-contrast detectability by using an advanced modeled iterative reconstruction (ADMIRE; Siemens Healthcare, Forchheim, Germany) algorithm in a contrast-detail phantom with a third-generation dual-source multidetector computed tomography (CT) scanner. MATERIALS AND METHODS: A proprietary phantom with a range of low-contrast cylindrical objects, representing five contrast levels (range, 5-20 HU) and three sizes (range, 2-6 mm) was fabricated with a three-dimensional printer and imaged with a third-generation dual-source CT scanner at various radiation dose index levels (range, 0.74-5.8 mGy). Image data sets were reconstructed by using different section thicknesses (range, 0.6-5.0 mm) and reconstruction algorithms (filtered back projection [FBP] and ADMIRE with a strength range of three to five). Eleven independent readers blinded to technique and reconstruction method assessed all data sets in two reading sessions by measuring detection accuracy with a two-alternative forced choice approach (first session) and by scoring the total number of visible object groups (second session). Dose reduction potentials based on both reading sessions were estimated. Results between FBP and ADMIRE were compared by using both paired t tests and analysis of variance tests at the 95% significance level. RESULTS: During the first session, detection accuracy increased with increasing contrast, size, and dose index (diagnostic accuracy range, 50%-87%; interobserver variability, ±7%). When compared with FBP, ADMIRE improved detection accuracy by 5.2% on average across the investigated variables (P < .001). During the second session, a significantly increased number of visible objects was noted with increasing radiation dose index, section thickness, and ADMIRE strength over FBP (up to 80% more visible objects, P < .001). Radiation dose reduction potential ranged from 56% to 60% and from 4% to 80% during the two sessions, respectively. CONCLUSION: Low-contrast detectability performance increased with increasing object size, object contrast, dose index, section thickness, and ADMIRE strength. Compared with FBP, ADMIRE allows a substantial radiation dose reduction while preserving low-contrast detectability. Online supplemental material is available for this article.

Authors
Solomon, J; Mileto, A; Ramirez-Giraldo, JC; Samei, E
MLA Citation
Solomon, J, Mileto, A, Ramirez-Giraldo, JC, and Samei, E. "Diagnostic Performance of an Advanced Modeled Iterative Reconstruction Algorithm for Low-Contrast Detectability with a Third-Generation Dual-Source Multidetector CT Scanner: Potential for Radiation Dose Reduction in a Multireader Study." Radiology 275.3 (June 2015): 735-745.
PMID
25751228
Source
epmc
Published In
Radiology
Volume
275
Issue
3
Publish Date
2015
Start Page
735
End Page
745
DOI
10.1148/radiol.15142005

TH-EF-BRA-07: A Reference Organ Dose Database for Body CT Examination Based On AAPM 246.

PURPOSE: This study aims to establish a reference organ dose database for clinical body CT based on detailed modeling of patient anatomy and irradiation condition. METHODS: Clinical CT images of 40 adult patients (age range: 18-78 y.o., 22 male, 18 female) were included. Each patient received a chest and abdominopelvic CT examination at our institution. Whole-body computer models were created from clinical CT data, which included most of the radiosensitive organs defined by ICRP Publication 103. A previously-validated Monte Carlo program was used to simulate organ dose for each patient model. The scanner spectrum, geometry and material information of the bowtie filter, and the tube current modulation (TCM) profiles were explicitly modeled. Three examination conditions were modeled: (1) fixed tube current (2) TCM exams with modest modulation strength (alpha = 0.5), and (3) TCM exams with strong modulation strength (alpha = 1).The calculated organ dose values were provided as a reference database for dosimetry benchmarking for chest and abdominopelvic examinations. RESULTS: Given the examination CTDIvol to be 7 mGy, organ dose for chest examination were in the range of 1.42 mGy to 14.4 mGy. For abdominopelvic examination, organ dose were in the range of 1.71 mGy to 10.5 mGy. Organ dose shows a gradual decrease with the increase of tube current modulation level. For chest scan, the average organ dose decreased 42.8% for the heart, and 25.0% for the lungs for strong modulation scans compared to no modulation. For abdominopelvic scan, the average organ dose decreased 33.8% for the stomach and 31.6% for the liver when implemented with strong TCM modulation compared to no modulation. CONCLUSION: A database of organ dose estimation is provided with information available for detailed modeling of the patient anatomy and scanner irradiation condition. Such database may be used as a reference standard in quantification and reporting of organ doses. Research fundings from GE, Siemens, and Carestream.

Authors
Tian, X; Segars, P; Andersson, J; Pavlicek, W; Samei, E
MLA Citation
Tian, X, Segars, P, Andersson, J, Pavlicek, W, and Samei, E. "TH-EF-BRA-07: A Reference Organ Dose Database for Body CT Examination Based On AAPM 246." Medical physics 42.6 (June 2015): 3746-.
PMID
26129614
Source
epmc
Published In
Medical physics
Volume
42
Issue
6
Publish Date
2015
Start Page
3746
DOI
10.1118/1.4926314

TH-AB-201-12: A Consumer Report for Mobile Digital Radiography: A Holistic Comparative Evaluation Across Four Systems.

PURPOSE: To provide a template for the comprehensive clinical evaluation of new imaging technologies with initial application to mobile digital radiography (DR). METHODS: Four mobile DR devices (GE Optima XR220amx+Flashpad; Carestream DRX Revolution+DRX-1C; Philips Mobile Diagnost wDR; Philips Mobile Diagnost wDR+Skyplate) were evaluated under four categories: 1)Technical specifications: Vendor data were collected and complied into a unified nomenclature. 2)Physical performance: Each unit underwent imaging physics evaluation including MTF, NPS, DQE, and grid artifact analysis. 3)Clinical performance: Fifteen bedside chest radiographs were acquired using each unit. Metadata were stripped and images cropped to 14:17 aspect ratio to ensure vendor anonymity. Six cardiothoracic radiologists scored the randomized images on PACS workstations using five criteria: overall quality, mediastinum noise, rib-lung contrast, lung density, and lung detail. Results were processed using multiple linear regression analysis. 4)Operability performance: A survey was designed and administered to technologists asking questions which captured use, preference, and experiential data for each unit. To avoid impropriety, units were randomly assigned numbers 1-4. RESULTS: Vendor specifications were compiled into a single-page table enabling ready comparative review. All systems had MTF within 20% and NNPS within 27% of the average response at frequencies below 2.5 mm(-1). Units [1,2,4] had DQE within 19% of average while unit 3 was 49% below average at high-frequencies. According to grid artifact analysis, the best and worst results were from units [2,3,4,1], respectively. The radiologist study revealed high inter-radiologist variability which limited the number of significant overall results. Survey results uncovered clear technologist biases. In general, technologists value practical over optional features. CONCLUSION: The compilation of vendor, physicist, radiologist, and technologist data provides an easy means for healthcare professionals to compare different medical equipment options using a data-driven approach. This type of comprehensive assessment now serves as a model for new technology review at our institution. This work was supported by Duke University Health Systems.

Authors
Wells, J; Christensen, J; Samei, E
MLA Citation
Wells, J, Christensen, J, and Samei, E. "TH-AB-201-12: A Consumer Report for Mobile Digital Radiography: A Holistic Comparative Evaluation Across Four Systems." Medical physics 42.6 (June 2015): 3720-.
PMID
26129495
Source
epmc
Published In
Medical physics
Volume
42
Issue
6
Publish Date
2015
Start Page
3720
DOI
10.1118/1.4926196

WE-G-204-09: Medical Physics 2.0 in Practice: Automated QC Assessment of Clinical Chest Images.

PURPOSE: To determine whether a proposed suite of objective image quality metrics for digital chest radiographs is useful for monitoring image quality in our clinical operation. METHODS: Seventeen gridless AP Chest radiographs from a GE Optima portable digital radiography (DR) unit (Group 1), seventeen (routine) PA Chest radiographs from a GE Discovery DR unit (Group 2), and sixteen gridless (non-routine) PA Chest radiographs from the same Discovery DR unit (Group 3) were chosen for analysis. Groups were selected to represent "sub-standard" (Group 1), "standard-of-care" (Group 2), and images with a gross technical error (Group 3). Group 1 images were acquired with lower kVp (90 vs. 125), shorter source-to-image distance (127cm vs 183cm) and were expected to have lower quality than images in Group 2. Group 3 was expected to have degraded contrast versus Group 2.This evaluation was approved by the institutional Quality Improvement Assurance Board (QIAB). Images were anonymized and securely transferred to the Duke University Clinical Imaging Physics Group for analysis using software previously described(1) and validated(2). Image quality for individual images was reported in terms of lung grey level(Lgl); lung noise(Ln); rib-lung contrast(RLc); rib sharpness(Rs); mediastinum detail(Md), noise(Mn), and alignment(Ma); subdiaphragm-lung contrast(SLc); and subdiaphragm area(Sa). Metrics were compared across groups. RESULTS: Metrics agreed with published Quality Consistency Ranges with three exceptions: higher Lgl, lower RLc, and SDc. Higher bit depth (16 vs 12) accounted for higher Lgl values in our images. Values were most internally consistent for Group 2. The most sensitive metric for distinguishing between groups was Mn followed closely by Ln. The least sensitive metrics were Md and RLc. CONCLUSION: The software appears promising for objectively and automatically identifying substandard images in our operation. The results can be used to establish local quality consistency ranges and action limits per facility preferences.

Authors
Willis, C; Willis, C; Nishino, T; Wells, J; Wilson, J; Samei, E
MLA Citation
Willis, C, Willis, C, Nishino, T, Wells, J, Wilson, J, and Samei, E. "WE-G-204-09: Medical Physics 2.0 in Practice: Automated QC Assessment of Clinical Chest Images." Medical physics 42.6 (June 2015): 3695-.
PMID
26129390
Source
epmc
Published In
Medical physics
Volume
42
Issue
6
Publish Date
2015
Start Page
3695
DOI
10.1118/1.4926093

WE-G-204-07: Automated Characterization of Perceptual Quality of Clinical Chest Radiographs: Improvements in Lung, Spine, and Hardware Detection.

PURPOSE: To develop and validate more robust methods for automated lung, spine, and hardware detection in AP/PA chest images. This work is part of a continuing effort to automatically characterize the perceptual image quality of clinical radiographs. [Y. Lin et al. Med. Phys. 39, 7019-7031 (2012)] METHODS: Our previous implementation of lung/spine identification was applicable to only one vendor. A more generalized routine was devised based on three primary components: lung boundary detection, fuzzy c-means (FCM) clustering, and a clinically-derived lung pixel probability map. Boundary detection was used to constrain the lung segmentations. FCM clustering produced grayscale- and neighborhood-based pixel classification probabilities which are weighted by the clinically-derived probability maps to generate a final lung segmentation. Lung centerlines were set along the left-right lung midpoints. Spine centerlines were estimated as a weighted average of body contour, lateral lung contour, and intensity-based centerline estimates. Centerline estimation was tested on 900 clinical AP/PA chest radiographs which included inpatient/outpatient, upright/bedside, men/women, and adult/pediatric images from multiple imaging systems. Our previous implementation further did not account for the presence of medical hardware (pacemakers, wires, implants, staples, stents, etc.) potentially biasing image quality analysis. A hardware detection algorithm was developed using a gradient-based thresholding method. The training and testing paradigm used a set of 48 images from which 1920 51×51 pixel(2) ROIs with and 1920 ROIs without hardware were manually selected. RESULTS: Acceptable lung centerlines were generated in 98.7% of radiographs while spine centerlines were acceptable in 99.1% of radiographs. Following threshold optimization, the hardware detection software yielded average true positive and true negative rates of 92.7% and 96.9%, respectively. CONCLUSION: Updated segmentation and centerline estimation methods in addition to new gradient-based hardware detection software provide improved data integrity control and error-checking for automated clinical chest image quality characterization across multiple radiography systems.

Authors
Wells, J; Zhang, L; Samei, E
MLA Citation
Wells, J, Zhang, L, and Samei, E. "WE-G-204-07: Automated Characterization of Perceptual Quality of Clinical Chest Radiographs: Improvements in Lung, Spine, and Hardware Detection." Medical physics 42.6 (June 2015): 3695-.
PMID
26129393
Source
epmc
Published In
Medical physics
Volume
42
Issue
6
Publish Date
2015
Start Page
3695
DOI
10.1118/1.4926091

MO-F-CAMPUS-I-03: GPU Accelerated Monte Carlo Technique for Fast Concurrent Image and Dose Simulation.

PURPOSE: To develop an accurate and fast Monte Carlo (MC) method of simulating CT that is capable of correlating dose with image quality using voxelized phantoms. METHODS: A realistic voxelized phantom based on patient CT data, XCAT, was used with a GPU accelerated MC code for helical MDCT. Simulations were done with both uniform density organs and with textured organs. The organ doses were validated using previous experimentally validated simulations of the same phantom under the same conditions. Images acquired by tracking photons through the phantom with MC require lengthy computation times due to the large number of photon histories necessary for accurate representation of noise. A substantial speed up of the process was attained by using a low number of photon histories with kernel denoising of the projections from the scattered photons. These FBP reconstructed images were validated against those that were acquired in simulations using many photon histories by ensuring a minimal normalized root mean square error. RESULTS: Organ doses simulated in the XCAT phantom are within 10% of the reference values. Corresponding images attained using projection kernel smoothing were attained with 3 orders of magnitude less computation time compared to a reference simulation using many photon histories. CONCLUSION: Combining GPU acceleration with kernel denoising of scattered photon projections in MC simulations allows organ dose and corresponding image quality to be attained with reasonable accuracy and substantially reduced computation time than is possible with standard simulation approaches.

Authors
Becchetti, M; Tian, X; Segars, P; Samei, E
MLA Citation
Becchetti, M, Tian, X, Segars, P, and Samei, E. "MO-F-CAMPUS-I-03: GPU Accelerated Monte Carlo Technique for Fast Concurrent Image and Dose Simulation." Medical physics 42.6 (June 2015): 3583-.
PMID
26128787
Source
epmc
Published In
Medical physics
Volume
42
Issue
6
Publish Date
2015
Start Page
3583
DOI
10.1118/1.4925488

TU-CD-207-08: Intrinsic Image Quality Comparison of Synthesized 2-D and FFDM Images.

PURPOSE: With the combined interest of managing patient dose, maintaining or improving image quality, and maintaining or improving the diagnostic utility of mammographic data, this study aims to compare the intrinsic image quality of Hologic's synthesized 2-D (C-View) and 2-D FFDM images in terms of resolution, contrast, and noise. METHODS: This study utilized a novel 3-D printed anthropomorphic breast phantom in addition to the American College of Radiology (ACR) mammography accreditation phantom. Analysis of the 3-D anthropomorphic phantom included visual assessment of resolution and analysis of the normalized noise power spectrum. Analysis of the ACR phantom included both visual inspection and objective automated analysis using in-house software. The software incorporates image- and object-specific CNR visibility thresholds which account for image characteristics such as noise texture which affect object visualization. T- test statistical analysis was also performed on ACR phantom scores. RESULTS: The spatial resolution of C-View images is markedly lower (at least 50% worse) than that of FFDM. And while this is generally associated with the benefit of reduced relative noise magnitude, the noise in C-View images tends to have a more mottled (predominantly low-frequency) texture. In general, for high contrast objects, C-View provides superior visualization over FFDM; however this benefit diminishes for low contrast objects and is applicable only to objects that are sufficiently larger than the spatial resolution threshold. Based on both observer and automated ACR phantom analysis, between 50-70% of C-View images failed to meet ACR minimum accreditation requirements - primarily due to insufficient (unbroken) fiber visibility. CONCLUSION: Compared to FFDM, C-View offers better depiction of objects of certain size and contrast, but provides poorer overall resolution and noise properties. Based on these findings, the utilization of C-View images in the clinical setting requires careful consideration, especially if considering the discontinuation of FFDM imaging.

Authors
Nelson, J; Wells, J; Samei, E
MLA Citation
Nelson, J, Wells, J, and Samei, E. "TU-CD-207-08: Intrinsic Image Quality Comparison of Synthesized 2-D and FFDM Images." Medical physics 42.6 (June 2015): 3611-.
PMID
26128927
Source
epmc
Published In
Medical physics
Volume
42
Issue
6
Publish Date
2015
Start Page
3611
DOI
10.1118/1.4925627

TU-G-204-04: A Unified Strategy for Bi-Factorial Optimization of Radiation Dose and Contrast Dose in CT Imaging.

PURPOSE: To substantiate the interdependency of contrast dose, radiation dose, and image quality in CT towards the patient- specific optimization of the imaging protocols METHODS: The study deployed two phantom platforms. A variable sized (12, 18, 23, 30, 37 cm) phantom (Mercury-3.0) containing an iodinated insert (8.5 mgI/ml) was imaged on a representative CT scanner at multiple CTDI values (0.7-22.6 mGy). The contrast and noise were measured from the reconstructed images for each phantom diameter. Linearly related to iodine-concentration, contrast-to-noise ratio (CNR), were calculated for 16 iodine-concentration levels (0-8.5 mgI/ml). The analysis was extended to a recently developed suit of 58 virtual human models (5D XCAT) with added contrast dynamics. Emulating a contrast-enhanced abdominal image procedure and targeting a peak-enhancement in aorta, each XCAT phantom was "imaged" using a simulation platform (CatSim, GE). 3D surfaces for each patient/size established the relationship between iodine-concentration, dose, and CNR. The ratios of change in iodine-concentration versus dose (IDR) to yield a constant change in CNR were calculated for each patient size. RESULTS: Mercury phantom results show the image-quality size- dependence on CTDI and IC levels. For desired image-quality values, the iso-contour-lines reflect the trade off between contrast-material and radiation doses. For a fixed iodine-concentration (4 mgI/mL), the IDR values for low (1.4 mGy) and high (11.5 mGy) dose levels were 1.02, 1.07, 1.19, 1.65, 1.54, and 3.14, 3.12, 3.52, 3.76, 4.06, respectively across five sizes. The simulation data from XCAT models confirmed the empirical results from Mercury phantom. CONCLUSION: The iodine-concentration, image quality, and radiation dose are interdependent. The understanding of the relationships between iodine-concentration, image quality, and radiation dose will allow for a more comprehensive optimization of CT imaging devices and techniques, providing the methodology to balance iodine-concentration and dose based on patient's attributes.

Authors
Sahbaee, P; Zhang, Y; Solomon, J; Becchetti, M; Segars, P; Samei, E
MLA Citation
Sahbaee, P, Zhang, Y, Solomon, J, Becchetti, M, Segars, P, and Samei, E. "TU-G-204-04: A Unified Strategy for Bi-Factorial Optimization of Radiation Dose and Contrast Dose in CT Imaging." June 2015.
PMID
26129067
Source
epmc
Published In
Medical physics
Volume
42
Issue
6
Publish Date
2015
Start Page
3633
DOI
10.1118/1.4925768

Automated Characterization of Perceptual Quality of Clinical Chest Radiographs: Improvements in Lung, Spine, and Hardware Detection

Authors
Wells, J; Zhang, L; Samei, E
MLA Citation
Wells, J, Zhang, L, and Samei, E. "Automated Characterization of Perceptual Quality of Clinical Chest Radiographs: Improvements in Lung, Spine, and Hardware Detection." June 2015.
Source
wos-lite
Published In
Medical physics
Volume
42
Issue
6
Publish Date
2015
Start Page
3695
End Page
3695

A Consumer Report for Mobile Digital Radiography: A Holistic Comparative Evaluation Across Four Systems

Authors
Wells, J; Christensen, J; Samei, E
MLA Citation
Wells, J, Christensen, J, and Samei, E. "A Consumer Report for Mobile Digital Radiography: A Holistic Comparative Evaluation Across Four Systems." June 2015.
Source
wos-lite
Published In
Medical physics
Volume
42
Issue
6
Publish Date
2015
Start Page
3720
End Page
3720

GPU Accelerated Monte Carlo Technique for Fast Concurrent Image and Dose Simulation

Authors
Becchetti, M; Tian, X; Segars, P; Samei, E
MLA Citation
Becchetti, M, Tian, X, Segars, P, and Samei, E. "GPU Accelerated Monte Carlo Technique for Fast Concurrent Image and Dose Simulation." June 2015.
Source
wos-lite
Published In
Medical physics
Volume
42
Issue
6
Publish Date
2015
Start Page
3583
End Page
3584

A Reference Organ Dose Database for Body CT Examination Based On AAPM 246

Authors
Tian, X; Segars, P; Andersson, J; Pavlicek, W; Samei, E
MLA Citation
Tian, X, Segars, P, Andersson, J, Pavlicek, W, and Samei, E. "A Reference Organ Dose Database for Body CT Examination Based On AAPM 246." June 2015.
Source
wos-lite
Published In
Medical physics
Volume
42
Issue
6
Publish Date
2015
Start Page
3746
End Page
3746

Intrinsic Image Quality Comparison of Synthesized 2-D and FFDM Images

Authors
Nelson, J; Wells, J; Samei, E
MLA Citation
Nelson, J, Wells, J, and Samei, E. "Intrinsic Image Quality Comparison of Synthesized 2-D and FFDM Images." June 2015.
Source
wos-lite
Published In
Medical physics
Volume
42
Issue
6
Publish Date
2015
Start Page
3611
End Page
3612

Medical Physics 2.0 in Practice: Automated QC Assessment of Clinical Chest Images

Authors
Willis, C; Willis, C; Nishino, T; Wells, J; Wilson, J; Samei, E
MLA Citation
Willis, C, Willis, C, Nishino, T, Wells, J, Wilson, J, and Samei, E. "Medical Physics 2.0 in Practice: Automated QC Assessment of Clinical Chest Images." June 2015.
Source
wos-lite
Published In
Medical physics
Volume
42
Issue
6
Publish Date
2015
Start Page
3695
End Page
3696

Prospective estimation of organ dose in CT under tube current modulation.

Computed tomography (CT) has been widely used worldwide as a tool for medical diagnosis and imaging. However, despite its significant clinical benefits, CT radiation dose at the population level has become a subject of public attention and concern. In this light, optimizing radiation dose has become a core responsibility for the CT community. As a fundamental step to manage and optimize dose, it may be beneficial to have accurate and prospective knowledge about the radiation dose for an individual patient. In this study, the authors developed a framework to prospectively estimate organ dose for chest and abdominopelvic CT exams under tube current modulation (TCM).The organ dose is mainly dependent on two key factors: patient anatomy and irradiation field. A prediction process was developed to accurately model both factors. To model the anatomical diversity and complexity in the patient population, the authors used a previously developed library of computational phantoms with broad distributions of sizes, ages, and genders. A selected clinical patient, represented by a computational phantom in the study, was optimally matched with another computational phantom in the library to obtain a representation of the patient's anatomy. To model the irradiation field, a previously validated Monte Carlo program was used to model CT scanner systems. The tube current profiles were modeled using a ray-tracing program as previously reported that theoretically emulated the variability of modulation profiles from major CT machine manufacturers Li et al., [Phys. Med. Biol. 59, 4525-4548 (2014)]. The prediction of organ dose was achieved using the following process: (1) CTDIvol-normalized-organ dose coefficients (horgan) for fixed tube current were first estimated as the prediction basis for the computational phantoms; (2) each computation phantom, regarded as a clinical patient, was optimally matched with one computational phantom in the library; (3) to account for the effect of the TCM scheme, a weighted organ-specific CTDIvol [denoted as CTDIvol organ,weighted] was computed for each organ based on the TCM profile and the anatomy of the "matched" phantom; (4) the organ dose was predicted by multiplying the weighted organ-specific CTDIvol with the organ dose coefficients (horgan). To quantify the prediction accuracy, each predicted organ dose was compared with the corresponding organ dose simulated from the Monte Carlo program with the TCM profile explicitly modeled.The predicted organ dose showed good agreements with the simulated organ dose across all organs and modulation profiles. The average percentage error in organ dose estimation was generally within 20% across all organs and modulation profiles, except for organs located in the pelvic and shoulder regions. For an average CTDIvol of a CT exam of 10 mGy, the average error at full modulation strength (α = 1) across all organs was 0.91 mGy for chest exams, and 0.82 mGy for abdominopelvic exams.This study developed a quantitative model to predict organ dose for clinical chest and abdominopelvic scans. Such information may aid in the design of optimized CT protocols in relation to a targeted level of image quality.

Authors
Tian, X; Li, X; Segars, WP; Frush, DP; Samei, E
MLA Citation
Tian, X, Li, X, Segars, WP, Frush, DP, and Samei, E. "Prospective estimation of organ dose in CT under tube current modulation." Medical physics 42.4 (April 2015): 1575-1585.
PMID
25832048
Source
epmc
Published In
Medical physics
Volume
42
Issue
4
Publish Date
2015
Start Page
1575
End Page
1585
DOI
10.1118/1.4907955

Comment on “Comparison of patient specific dose metrics between chest radiography, tomosynthesis, and CT for adult patients of wide ranging body habitus” [Med. Phys. 41(2), 023901 (12pp.) (2014)].

Authors
Samei, E; Zhang, Y; Christianson, O
MLA Citation
Samei, E, Zhang, Y, and Christianson, O. "Comment on “Comparison of patient specific dose metrics between chest radiography, tomosynthesis, and CT for adult patients of wide ranging body habitus” [Med. Phys. 41(2), 023901 (12pp.) (2014)]." Medical physics 42.4 (April 2015): 2094-.
PMID
25832099
Source
epmc
Published In
Medical physics
Volume
42
Issue
4
Publish Date
2015
Start Page
2094
DOI
10.1118/1.4914374

Comment on “Comparison of patient specific dose metrics between chest radiography, tomosynthesis, and CT for adult patients of wide ranging body habitus” [Med. Phys. 41(2), 023901 (12pp.) (2014)]

Authors
Samei, E; Zhang, Y; Christianson, O
MLA Citation
Samei, E, Zhang, Y, and Christianson, O. "Comment on “Comparison of patient specific dose metrics between chest radiography, tomosynthesis, and CT for adult patients of wide ranging body habitus” [Med. Phys. 41(2), 023901 (12pp.) (2014)]." Medical Physics 42.4 (March 31, 2015): 2094-2095.
Source
crossref
Published In
Medical physics
Volume
42
Issue
4
Publish Date
2015
Start Page
2094
End Page
2095
DOI
10.1118/1.4914374

Implementation of the ACR Dose Index Registry.

Authors
Wilson, JM; Samei, E
MLA Citation
Wilson, JM, and Samei, E. "Implementation of the ACR Dose Index Registry." Journal of the American College of Radiology : JACR 12.3 (March 2015): 312-313.
PMID
25743926
Source
epmc
Published In
Journal of the American College of Radiology
Volume
12
Issue
3
Publish Date
2015
Start Page
312
End Page
313
DOI
10.1016/j.jacr.2014.11.019

A multireader diagnostic performance study of low-contrast detectability on a third-generation dual-source CT scanner: Filtered back projection versus advanced modeled iterative reconstruction

© 2015 SPIE.The purpose of this work was to compare CT low-contrast detectability between two reconstruction algorithms, filtered back-projection (FBP) and advanced modeled iterative reconstruction (ADMIRE). A phantom was designed with a range of low-contrast circular inserts representing 5 contrast levels and 3 sizes. The phantom was imaged on a third-generation dual-source CT scanner (SOMATOM Definition Force, Siemens Healthcare) under various dose levels (0.74-5.8 mGy CTDIVol). Images were reconstructed using different settings of slice thickness (0.6-5 mm) and reconstruction algorithms (FBP and ADMIRE with strength of 3-5) and were assessed by eleven blinded and independent readers using a two alternative forced choice (2AFC) detection experiment. A second observer experiment was further performed in which observers scored the images based on the total number of visible object groups. Detection performance increased with increasing contrast, size, dose, with accuracy ranging from 50% (i.e., guessing) to 87% with an average inter-observer variability of ±7%. The use of ADMIRE-3 increased performance by 5.2% resulting in an estimated dose reduction potential of 56-60%. The results from the second experiment also showed increased number of visible object groups for increasing dose, slice thickness, and ADMIRE strength. The score difference between FBP and ADMIRE was 0.9, 1.3, and 2.1 for ADMIRE strengths of 3, 4, and 5, respectively, resulting in estimated dose reduction potentials between 4-80%. Overall, the data indicated potential to image at reduced doses while maintaining comparable image quality when using ADMIRE compared to FBP.

Authors
Solomon, J; Mileto, A; Ramirez-Giraldo, JC; Samei, E
MLA Citation
Solomon, J, Mileto, A, Ramirez-Giraldo, JC, and Samei, E. "A multireader diagnostic performance study of low-contrast detectability on a third-generation dual-source CT scanner: Filtered back projection versus advanced modeled iterative reconstruction." January 1, 2015.
Source
scopus
Published In
Proceedings of SPIE
Volume
9416
Publish Date
2015
DOI
10.1117/12.2081647

What observer models best reflect low-contrast detectability in CT?

© 2015 SPIE.The purpose of this work was to compare CT low-contrast detectability as measured via human perception experiments with observer model surrogates of image quality measured directly from the images. A phantom was designed with a range of low-contrast circular inserts representing 5 contrast levels and 3 sizes. The phantom was imaged repeatedly (20 times) on a third-generation dual-source CT scanner (SOMATOM Definition Force, Siemens Healthcare). Images were reconstructed at 0.6 mm slice thickness using filtered back projection (FBP) and advanced modeled iterative reconstruction (ADMIRE) and were assessed by eleven blinded and independent readers using a two alternative forced choice (2AFC) detection experiment. The human scores were taken as the accuracy, averaged across observers. The predicted performance was computed directly from the images for several traditional image quality metrics and model observers including contrast to noise ratio (CNR), area weighted CNR (CNRa), non-prewhitening matched filter (NPW), non-prewhitening matched filter with an eye filter (NPWE), channelized Hotelling observer (CHO), and channelized Hotelling observer with internal noise (CHOi). The correlation between model observer predictions and human performance was assessed using linear regression analysis. The coefficient of determination (R2) was used as goodness-of-fit metric to determine how well each model observer predicts human performance. R2 was 0.11, 0.71, 0.73, 0.77, 0.60, and 0.72 for CNR, CNRa, NPW, NPWE, CHO, and CHOi, respectively. The findings demonstrate NPW, NPWE, and CHOi all to have strong correlation with human performance and could be used to optimize scan and reconstruction settings.

Authors
Solomon, J; Samei, E
MLA Citation
Solomon, J, and Samei, E. "What observer models best reflect low-contrast detectability in CT?." January 1, 2015.
Source
scopus
Published In
Proceedings of SPIE
Volume
9416
Publish Date
2015
DOI
10.1117/12.2081655

The impact of breast structure on lesion detection in breast tomosynthesis

© 2015 SPIE.Virtual clinical trials (VCT) can be carefully designed to inform, orient, or potentially replace clinical trials. The focus of this study was to demonstrate the capability of the sophisticated tools that can be used in the design, implementation, and performance analysis of VCTs, through characterization of the effect of background tissue density and heterogeneity on the detection of irregular masses in digital breast tomosynthesis. Twenty breast phantoms from the extended cardiactorso (XCAT) family, generated based on dedicated breast computed tomography of human subjects, were used to extract a total of 2173 volumes of interest (VOI) from simulated tomosynthesis images. Five different lesions, modeled after human subject tomosynthesis images, were embedded in the breasts, for a total of 6×2173 VOIs with and without lesions. Effects of background tissue density and heterogeneity on the detection of the lesions were studied by implementing a doubly composite hypothesis signal detection theory paradigm with location known exactly, lesion known exactly, and background known statistically. The results indicated that the detection performance as measured by the area under the receiver operating characteristic curve (ROC) deteriorated as density was increased, yielding findings consistent with clinical studies. The detection performance varied substantially across the twenty breasts. Furthermore, the log-likelihood ratio under H0 and H1seemed to be affected by background tissue density and heterogeneity differently. Considering background tissue variability can change the outcomes of a VCT and is hence of crucial importance. The XCAT breast phantoms can address this concern by offering realistic modeling of background tissue variability based on a wide range of human subjects.

Authors
Kiarashi, N; Nolte, LW; Lo, JY; Segars, WP; Ghate, SV; Samei, E
MLA Citation
Kiarashi, N, Nolte, LW, Lo, JY, Segars, WP, Ghate, SV, and Samei, E. "The impact of breast structure on lesion detection in breast tomosynthesis." January 1, 2015.
Source
scopus
Published In
Proceedings of SPIE
Volume
9412
Publish Date
2015
DOI
10.1117/12.2082473

Experimental implementation of coded aperture coherent scatter spectral imaging of cancerous and healthy breast tissue samples

© 2015 SPIE.A fast and accurate scatter imaging technique to differentiate cancerous and healthy breast tissue is introduced in this work. Such a technique would have wide-ranging clinical applications from intra-operative margin assessment to breast cancer screening. Coherent Scatter Computed Tomography (CSCT) has been shown to differentiate cancerous from healthy tissue, but the need to raster scan a pencil beam at a series of angles and slices in order to reconstruct 3D images makes it prohibitively time consuming. In this work we apply the coded aperture coherent scatter spectral imaging technique to reconstruct 3D images of breast tissue samples from experimental data taken without the rotation usually required in CSCT. We present our experimental implementation of coded aperture scatter imaging, the reconstructed images of the breast tissue samples and segmentations of the 3D images in order to identify the cancerous and healthy tissue inside of the samples. We find that coded aperture scatter imaging is able to reconstruct images of the samples and identify the distribution of cancerous and healthy tissues (i.e., fibroglandular, adipose, or a mix of the two) inside of them. Coded aperture scatter imaging has the potential to provide scatter images that automatically differentiate cancerous and healthy tissue inside of ex vivo samples within a time on the order of a minute.

Authors
Lakshmanan, MN; Greenberg, JA; Samei, E; Kapadia, AJ
MLA Citation
Lakshmanan, MN, Greenberg, JA, Samei, E, and Kapadia, AJ. "Experimental implementation of coded aperture coherent scatter spectral imaging of cancerous and healthy breast tissue samples." January 1, 2015.
Source
scopus
Published In
Proceedings of SPIE
Volume
9412
Publish Date
2015
DOI
10.1117/12.2082318

A quantitative metrology for performance characterization of breast tomosynthesis systems based on an anthropomorphic phantom

© 2015 SPIE.Purpose: Common methods for assessing image quality of digital breast tomosynthesis (DBT) devices currently utilize simplified or otherwise unrealistic phantoms, which use inserts in a uniform background and gauge performance based on a subjective evaluation of insert visibility. This study proposes a different methodology to assess system performance using a three-dimensional clinically-informed anthropomorphic breast phantom. Methods: The system performance is assessed by imaging the phantom and computationally characterizing the resultant images in terms of several new metrics. These include a contrast index (reflective of local difference between adipose and glandular material), a contrast to noise ratio index (reflective of contrast against local background noise), and a nonuniformity index (reflective of contributions of noise and artifacts within uniform adipose regions). Indices were measured at ROI sizes of 10mm and 37 mm, respectively. The method was evaluated at fixed dose of 1.5 mGy AGD. Results: Results indicated notable differences between systems. At 10 mm, vendor A had the highest contrast index, followed by B and C in that. The performance ranking was identical at the largest ROI size. The non-uniformity index similarly exhibited system-dependencies correlated with visual appearance of clutter from out-of-plane artifacts. Vendor A had the greatest NI at all ROI sizes, B had the second greatest, and C the least. Conclusions: The findings illustrate that the anthropomorphic phantom can be used as a quality control tool with results that are targeted to be more reflective of clinical performance of breast tomosynthesis systems of multiple manufacturers.

Authors
Ikejimba, L; Chen, Y; Oberhofer, N; Kiarashi, N; Lo, JY; Samei, E
MLA Citation
Ikejimba, L, Chen, Y, Oberhofer, N, Kiarashi, N, Lo, JY, and Samei, E. "A quantitative metrology for performance characterization of breast tomosynthesis systems based on an anthropomorphic phantom." January 1, 2015.
Source
scopus
Published In
Proceedings of SPIE
Volume
9412
Publish Date
2015
DOI
10.1117/12.2082594

Determination of contrast media administration to achieve a targeted contrast enhancement in CT

© 2015 SPIE.Contrast enhancement is a key component of CT imaging and offer opportunities for optimization. The design and optimization of new techniques however requires orchestration with the scan parameters and further a methodology to relate contrast enhancement and injection function. In this study, we used such a methodology to develop a method, analytical inverse method, to predict the required injection function to achieve a desired contrast enhancement in a given organ by incorporation of a physiologically based compartmental model. The method was evaluated across 32 different target contrast enhancement functions for aorta, kidney, stomach, small intestine, and liver. The results exhibited that the analytical inverse method offers accurate performance with error in the range of 10% deviation between the predicted and desired organ enhancement curves. However, this method is incapable of predicting the injection function based on the liver enhancement. The findings of this study can be useful in optimizing contrast medium injection function as well as the scan timing to provide more consistency in the way that the contrast enhanced CT examinations are performed. To our knowledge, this work is one of the first attempts to predict the contrast material injection function for a desired organ enhancement curve.

Authors
Sahbaee, P; Li, Y; Segars, P; Marin, D; Nelson, R; Samei, E
MLA Citation
Sahbaee, P, Li, Y, Segars, P, Marin, D, Nelson, R, and Samei, E. "Determination of contrast media administration to achieve a targeted contrast enhancement in CT." January 1, 2015.
Source
scopus
Published In
Proceedings of SPIE
Volume
9412
Publish Date
2015
DOI
10.1117/12.2082261

Convolution-based estimation of organ dose in tube current modulated CT

© 2015 SPIE.Among the various metrics that quantify radiation dose in computed tomography (CT), organ dose is one of the most representative quantities reflecting patient-specific radiation burden.1 Accurate estimation of organ dose requires one to effectively model the patient anatomy and the irradiation field. As illustrated in previous studies, the patient anatomy factor can be modeled using a library of computational phantoms with representative body habitus.2 However, the modeling of irradiation field can be practically challenging, especially for CT exams performed with tube current modulation. The central challenge is to effectively quantify the scatter irradiation field created by the dynamic change of tube current. In this study, we present a convolution-based technique to effectively quantify the primary and scatter irradiation field for TCM examinations. The organ dose for a given clinical patient can then be rapidly determined using the convolution-based method, a patient-matching technique, and a library of computational phantoms. 58 adult patients were included in this study (age range: 18-70 y.o., weight range: 60-180 kg). One computational phantom was created based on the clinical images of each patient. Each patient was optimally matched against one of the remaining 57 computational phantoms using a leave-one-out strategy. For each computational phantom, the organ dose coefficients (CTDIvol-normalized organ dose) under fixed tube current were simulated using a validated Monte Carlo simulation program. Such organ dose coefficients were multiplied by a scaling factor, (CTDIvol)organ, convolution that quantifies the regional irradiation field. The convolution-based organ dose was compared with the organ dose simulated from Monte Carlo program with TCM profiles explicitly modeled on the original phantom created based on patient images. The estimation error was within 10% across all organs and modulation profiles for abdominopelvic examination. This strategy enables prospective and retrospective patient-specific dose estimation without the need of Monte Carlo simulation.

Authors
Tian, X; Segars, WP; Dixon, RL; Samei, E
MLA Citation
Tian, X, Segars, WP, Dixon, RL, and Samei, E. "Convolution-based estimation of organ dose in tube current modulated CT." January 1, 2015.
Source
scopus
Published In
Proceedings of SPIE
Volume
9412
Publish Date
2015
DOI
10.1117/12.2082238

Assessment of the dose reduction potential of a model-based iterative reconstruction algorithm using a task-based performance metrology.

Different computed tomography (CT) reconstruction techniques offer different image quality attributes of resolution and noise, challenging the ability to compare their dose reduction potential against each other. The purpose of this study was to evaluate and compare the task-based imaging performance of CT systems to enable the assessment of the dose performance of a model-based iterative reconstruction (MBIR) to that of an adaptive statistical iterative reconstruction (ASIR) and a filtered back projection (FBP) technique.The ACR CT phantom (model 464) was imaged across a wide range of mA setting on a 64-slice CT scanner (GE Discovery CT750 HD, Waukesha, WI). Based on previous work, the resolution was evaluated in terms of a task-based modulation transfer function (MTF) using a circular-edge technique and images from the contrast inserts located in the ACR phantom. Noise performance was assessed in terms of the noise-power spectrum (NPS) measured from the uniform section of the phantom. The task-based MTF and NPS were combined with a task function to yield a task-based estimate of imaging performance, the detectability index (d'). The detectability index was computed as a function of dose for two imaging tasks corresponding to the detection of a relatively small and a relatively large feature (1.5 and 25 mm, respectively). The performance of MBIR in terms of the d' was compared with that of ASIR and FBP to assess its dose reduction potential.Results indicated that MBIR exhibits a variability spatial resolution with respect to object contrast and noise while significantly reducing image noise. The NPS measurements for MBIR indicated a noise texture with a low-pass quality compared to the typical midpass noise found in FBP-based CT images. At comparable dose, the d' for MBIR was higher than those of FBP and ASIR by at least 61% and 19% for the small feature and the large feature tasks, respectively. Compared to FBP and ASIR, MBIR indicated a 46%-84% dose reduction potential, depending on task, without compromising the modeled detection performance.The presented methodology based on ACR phantom measurements extends current possibilities for the assessment of CT image quality under the complex resolution and noise characteristics exhibited with statistical and iterative reconstruction algorithms. The findings further suggest that MBIR can potentially make better use of the projections data to reduce CT dose by approximately a factor of 2. Alternatively, if the dose held unchanged, it can improve image quality by different levels for different tasks.

Authors
Samei, E; Richard, S
MLA Citation
Samei, E, and Richard, S. "Assessment of the dose reduction potential of a model-based iterative reconstruction algorithm using a task-based performance metrology." Medical physics 42.1 (January 2015): 314-323.
PMID
25563271
Source
epmc
Published In
Medical physics
Volume
42
Issue
1
Publish Date
2015
Start Page
314
End Page
323
DOI
10.1118/1.4903899

Dual-energy MDCT in hypervascular liver tumors: effect of body size on selection of the optimal monochromatic energy level.

OBJECTIVE: The purpose of this article is to investigate the effect of body size on the selection of optimal monochromatic energy level for maximizing the conspicuity of hypervascular liver tumors during late hepatic arterial phase using dual-energy MDCT. MATERIALS AND METHODS: An anthropomorphic liver phantom in three body sizes and iodine-containing inserts simulating low- and high-contrast hypervascular lesions was imaged with dual- and single-energy MDCT at various energy levels (80, 100, 120, and 140 kVp). Dual-energy MDCT was also performed in 48 patients with 114 hypervascular liver tumors; virtual monochromatic images were reconstructed at energy levels from 40 to 140 keV. The effect of body size and lesion iodine concentration on noise and tumor-to-liver contrast-to-noise ratio was compared among different datasets for phantoms and patients. RESULTS: The highest tumor-to-liver contrast-to-noise ratio was noted at 80 kVp for all phantom sizes. On virtual monochromatic images, the minimum noise was noted at 70 keV for small and medium phantoms and at 80 keV for the large phantom. Tumor-to-liver contrast-to-noise ratio was highest at 50 keV for small and medium phantoms and at 60 keV for the large phantom (p<0.0001). Compared with 80-kVp images, an optimal monochromatic energy level yielded a significantly higher (p<0.0001) tumor-to-liver contrast-to-noise ratio for high-contrast lesions in the large body size and for low-contrast lesions in all phantom sizes. In patients, the optimal monochromatic energy level for tumor-to-liver contrast-to-noise ratio increased proportionally along with body size (p<0.0001). CONCLUSION: Selection of the optimal monochromatic energy level for maximizing the conspicuity of hypervascular liver tumors is significantly affected by patient's body size.

Authors
Mileto, A; Nelson, RC; Samei, E; Choudhury, KR; Jaffe, TA; Wilson, JM; Marin, D
MLA Citation
Mileto, A, Nelson, RC, Samei, E, Choudhury, KR, Jaffe, TA, Wilson, JM, and Marin, D. "Dual-energy MDCT in hypervascular liver tumors: effect of body size on selection of the optimal monochromatic energy level." AJR. American journal of roentgenology 203.6 (December 2014): 1257-1264.
PMID
25415703
Source
epmc
Published In
AJR. American journal of roentgenology
Volume
203
Issue
6
Publish Date
2014
Start Page
1257
End Page
1264
DOI
10.2214/ajr.13.12229

Evaluating iterative reconstruction performance in computed tomography.

Iterative reconstruction (IR) offers notable advantages in computed tomography (CT). However, its performance characterization is complicated by its potentially nonlinear behavior, impacting performance in terms of specific tasks. This study aimed to evaluate the performance of IR with both task-specific and task-generic strategies.The performance of IR in CT was mathematically assessed with an observer model that predicted the detection accuracy in terms of the detectability index (d'). d' was calculated based on the properties of the image noise and resolution, the observer, and the detection task. The characterizations of image noise and resolution were extended to accommodate the nonlinearity of IR. A library of tasks was mathematically modeled at a range of sizes (radius 1-4 mm), contrast levels (10-100 HU), and edge profiles (sharp and soft). Unique d' values were calculated for each task with respect to five radiation exposure levels (volume CT dose index, CTDIvol: 3.4-64.8 mGy) and four reconstruction algorithms (filtered backprojection reconstruction, FBP; iterative reconstruction in imaging space, IRIS; and sinogram affirmed iterative reconstruction with strengths of 3 and 5, SAFIRE3 and SAFIRE5; all provided by Siemens Healthcare, Forchheim, Germany). The d' values were translated into the areas under the receiver operating characteristic curve (AUC) to represent human observer performance. For each task and reconstruction algorithm, a threshold dose was derived as the minimum dose required to achieve a threshold AUC of 0.9. A task-specific dose reduction potential of IR was calculated as the difference between the threshold doses for IR and FBP. A task-generic comparison was further made between IR and FBP in terms of the percent of all tasks yielding an AUC higher than the threshold.IR required less dose than FBP to achieve the threshold AUC. In general, SAFIRE5 showed the most significant dose reduction potentials (11-54 mGy, 77%-84%), followed by SAFIRE3 (7-36 mGy, 50%-61%) and IRIS (6-26 mGy, 37%-50%). The dose reduction potentials highly depended on task size and task contrast, with tasks of lower contrasts and smaller sizes, i.e., more challenging tasks, indicating higher dose reductions. Softer edge profile showed higher dose reduction potentials with SAFIRE3 and SAFIRE5, but not with IRIS. The task-generic comparison between IR and FBP demonstrated the overall superiority of IR performance, as IR allowed a larger percent of tasks to exceed the threshold AUC: IRIS, 8%-12%; SAFIRE3, 10%-16%; and SAFIRE5, 20%-33%. The improvement with IR was generally more pronounced at lower dose levels.Expanding beyond traditional contrast and noise based assessments of IR, we performed both task-specific and task-generic evaluations of IR performance. The task-specific evaluation demonstrated the dependency of IR's dose reduction potential on task attributes, which can be employed to optimize IR for clinical indications with specific range of size and contrast. The task-generic evaluation demonstrated IR's overall superiority over FBP in terms of the range of tasks exceeding a threshold performance level, which can be employed for general comparisons between algorithms.

Authors
Chen, B; Ramirez Giraldo, JC; Solomon, J; Samei, E
MLA Citation
Chen, B, Ramirez Giraldo, JC, Solomon, J, and Samei, E. "Evaluating iterative reconstruction performance in computed tomography." Medical physics 41.12 (December 2014): 121913-.
PMID
25471973
Source
epmc
Published In
Medical physics
Volume
41
Issue
12
Publish Date
2014
Start Page
121913
DOI
10.1118/1.4901670

Organ localization: toward prospective patient-specific organ dosimetry in computed tomography.

With increased focus on radiation dose from medical imaging, prospective radiation dose estimates are becoming increasingly desired. Using available populations of adult and pediatric patient phantoms, radiation dose calculations can be catalogued and prospectively applied to individual patients that best match certain anatomical characteristics. In doing so, the knowledge of organ size and location is a required element. Here, the authors develop a predictive model of organ locations and volumes based on an analysis of adult and pediatric computed tomography (CT) data.Fifty eight adult and 69 pediatric CT datasets were segmented and utilized in the study. The maximum and minimum points of the organs were recorded with respect to the axial distance from the tip of the sacrum. The axial width, midpoint, and volume of each organ were calculated. Linear correlations between these three organ parameters and patient age, BMI, weight, and height were determined.No statistically significant correlations were found in adult patients between the axial width, midpoint, and volume of the organs versus the patient age or BMI. Slight, positive linear trends were found for organ midpoint versus patient weight (max r(2) = 0.382, mean r(2) = 0.236). Similar trends were found for organ midpoint versus height (max r(2) = 0.439, mean r(2) = 0.200) and for organ volume versus height (max r(2) = 0.410, mean r(2) = 0.153). Gaussian fits performed on probability density functions of the adult organs resulted in r(2)-values ranging from 0.96 to 0.996. The pediatric patients showed much stronger correlations overall. Strong correlations were observed between organ axial midpoint versus age, height, and weight (max r(2) = 0.842, mean r(2) = 0.790; max r(2) = 0.949, mean r(2) = 0.894; and max r(2) = 0.870, mean r(2) = 0.847, respectively). Moderate linear correlations were also observed for organ axial width versus height (max r(2) = 0.772, mean r(2) = 0.562) and for organ volume versus height (max r(2) = 0.781, mean r(2) = 0.601).Adult patients exhibited small variations in organ volume and location with respect to height and weight, but no meaningful correlation existed between these parameters and age or BMI. Once adulthood is reached, organ morphology and positioning seem to remain static. However, clear trends are evident between pediatric organ locations versus age, height, and weight. Such information can be incorporated into a matching methodology that may provide the highest probability of representing the anatomy of a patient undergoing a clinical exam to prospectively estimate the radiation dose.

Authors
Segars, WP; Rybicki, K; Norris, H; Frush, D; Samei, E
MLA Citation
Segars, WP, Rybicki, K, Norris, H, Frush, D, and Samei, E. "Organ localization: toward prospective patient-specific organ dosimetry in computed tomography." Medical physics 41.12 (December 2014): 121908-.
PMID
25471968
Source
epmc
Published In
Medical physics
Volume
41
Issue
12
Publish Date
2014
Start Page
121908
DOI
10.1118/1.4901554

A generic framework to simulate realistic lung, liver and renal pathologies in CT imaging.

Realistic three-dimensional (3D) mathematical models of subtle lesions are essential for many computed tomography (CT) studies focused on performance evaluation and optimization. In this paper, we develop a generic mathematical framework that describes the 3D size, shape, contrast, and contrast-profile characteristics of a lesion, as well as a method to create lesion models based on CT data of real lesions. Further, we implemented a technique to insert the lesion models into CT images in order to create hybrid CT datasets. This framework was used to create a library of realistic lesion models and corresponding hybrid CT images. The goodness of fit of the models was assessed using the coefficient of determination (R(2)) and the visual appearance of the hybrid images was assessed with an observer study using images of both real and simulated lesions and receiver operator characteristic (ROC) analysis. The average R(2) of the lesion models was 0.80, implying that the models provide a good fit to real lesion data. The area under the ROC curve was 0.55, implying that the observers could not readily distinguish between real and simulated lesions. Therefore, we conclude that the lesion-modeling framework presented in this paper can be used to create realistic lesion models and hybrid CT images. These models could be instrumental in performance evaluation and optimization of novel CT systems.

Authors
Solomon, J; Samei, E
MLA Citation
Solomon, J, and Samei, E. "A generic framework to simulate realistic lung, liver and renal pathologies in CT imaging." Physics in medicine and biology 59.21 (November 2014): 6637-6657.
PMID
25325156
Source
epmc
Published In
Physics in Medicine and Biology
Volume
59
Issue
21
Publish Date
2014
Start Page
6637
End Page
6657
DOI
10.1088/0031-9155/59/21/6637

Automated characterization of perceptual quality of clinical chest radiographs: validation and calibration to observer preference.

The authors previously proposed an image-based technique [Y. Lin et al. Med. Phys. 39, 7019-7031 (2012)] to assess the perceptual quality of clinical chest radiographs. In this study, an observer study was designed and conducted to validate the output of the program against rankings by expert radiologists and to establish the ranges of the output values that reflect the acceptable image appearance so the program output can be used for image quality optimization and tracking.Using an IRB-approved protocol, 2500 clinical chest radiographs (PA/AP) were collected from our clinical operation. The images were processed through our perceptual quality assessment program to measure their appearance in terms of ten metrics of perceptual image quality: lung gray level, lung detail, lung noise, rib-lung contrast, rib sharpness, mediastinum detail, mediastinum noise, mediastinum alignment, subdiaphragm-lung contrast, and subdiaphragm area. From the results, for each targeted appearance attribute/metric, 18 images were selected such that the images presented a relatively constant appearance with respect to all metrics except the targeted one. The images were then incorporated into a graphical user interface, which displayed them into three panels of six in a random order. Using a DICOM calibrated diagnostic display workstation and under low ambient lighting conditions, each of five participating attending chest radiologists was tasked to spatially order the images based only on the targeted appearance attribute regardless of the other qualities. Once ordered, the observer also indicated the range of image appearances that he/she considered clinically acceptable. The observer data were analyzed in terms of the correlations between the observer and algorithmic rankings and interobserver variability. An observer-averaged acceptable image appearance was also statistically derived for each quality attribute based on the collected individual acceptable ranges.The observer study indicated that, for each image quality attribute, the averaged observer ranking strongly correlated with the algorithmic ranking (linear correlation coefficient R > 0.92), with highest correlation (R = 1) for lung gray level and the lowest (R = 0.92) for mediastinum noise. There was a strong concordance between the observers in terms of their rankings (i.e., Kendall's tau agreement > 0.84). The observers also generally indicated similar tolerance and preference levels in terms of acceptable ranges, as 85% of the values were close to the overall tolerance or preference levels and the differences were smaller than 0.15.The observer study indicates that the previously proposed technique provides a robust reflection of the perceptual image quality in clinical images. The results established the range of algorithmic outputs for each metric that can be used to quantitatively assess and qualify the appearance quality of clinical chest radiographs.

Authors
Samei, E; Lin, Y; Choudhury, KR; McAdams, HP
MLA Citation
Samei, E, Lin, Y, Choudhury, KR, and McAdams, HP. "Automated characterization of perceptual quality of clinical chest radiographs: validation and calibration to observer preference." Medical physics 41.11 (November 2014): 111918-.
PMID
25370651
Source
epmc
Published In
Medical physics
Volume
41
Issue
11
Publish Date
2014
Start Page
111918
DOI
10.1118/1.4899183

Determining organ dose: the holy grail.

Among the various metrics to quantify CT radiation dose, organ dose is generally regarded as one of the best to reflect patient radiation burden. Organ dose is dependent on two main factors, namely patient anatomy and irradiation field. An accurate estimation of organ dose requires detailed modeling of both factors. The modeling of patient anatomy needs to reflect the anatomical diversity and complexity across the population so that the attributes of a given clinical patient can be properly accounted for. The modeling of the irradiation field needs to accurately reflect the CT system condition, especially the tube current modulation (TCM) technique. We present an atlas-based method to model patient anatomy via a library of computational phantoms with representative ages, sizes and genders. A clinical patient is matched with a corresponding computational phantom to obtain a representation of patient anatomy. The irradiation field of the CT system is modeled using a validated Monte Carlo simulation program. The tube current modulation profiles are simulated using a manufacturer-generalizable ray-tracing algorithm. Combining the patient model, Monte Carlo results, and TCM profile, organ doses are obtained by multiplying organ dose values from a fixed mA scan (normalized to CTDIvol-normalized, denoted as h organ ) and an adjustment factor that reflects the specific irradiation of each organ. The accuracy of the proposed method was quantified by simulating clinical abdominopelvic examinations of 58 patients. The predicted organ doses showed good agreement with simulated organ dose across all organs and modulation schemes. For an average CTDIvol of a CT exam of 10 mGy, the absolute median error across all organs was 0.64 mGy (-0.21 and 0.97 for 25th and 75th percentiles, respectively). The percentage differences were within 15%. The study demonstrates that it is feasible to estimate organ doses in clinical CT examinations for protocols without and with tube current modulation. The methodology can be used for both prospective and retrospective estimation of organ dose.

Authors
Samei, E; Tian, X; Segars, WP
MLA Citation
Samei, E, Tian, X, and Segars, WP. "Determining organ dose: the holy grail." Pediatric radiology 44 Suppl 3 (October 11, 2014): 460-467.
PMID
25304705
Source
epmc
Published In
Pediatric Radiology
Volume
44 Suppl 3
Publish Date
2014
Start Page
460
End Page
467
DOI
10.1007/s00247-014-3117-7

Pros and cons of organ shielding for CT imaging.

With the increased importance of CT radiation dose to health care providers, patients and the general public, there is an increased responsibility to minimize patient dose effectively. Bismuth shields offer a simple strategy to reduce dose to certain anterior radiosensitive organs such as breasts and eyes. However, in order to reduce organ dose they must be used properly; improper use can lead to an actual increase in the patient dose. They also create a proportional increase in image noise in the section of the body adjacent to the shield and further reduce the quantitative precision of CT numbers. In addition, shielding can degrade the overall efficiency (by an order of approximately 10%) of the imaging process, reducing the theoretical image quality that can be expected from a certain level of patient dose. However, in spite of their significant disadvantages, there are certain clinical situations and practice considerations that provide qualified justification for their continued use.

Authors
Samei, E
MLA Citation
Samei, E. "Pros and cons of organ shielding for CT imaging." Pediatric radiology 44 Suppl 3 (October 11, 2014): 495-500.
PMID
25304710
Source
epmc
Published In
Pediatric Radiology
Volume
44 Suppl 3
Publish Date
2014
Start Page
495
End Page
500
DOI
10.1007/s00247-014-3084-z

Impact of dual-energy multi-detector row CT with virtual monochromatic imaging on renal cyst pseudoenhancement: in vitro and in vivo study.

PURPOSE: To investigate whether dual-energy multi-detector row computed tomography (CT) with virtual monochromatic imaging can overcome renal cyst pseudoenhancement in a phantom experiment and a clinical study. MATERIALS AND METHODS: This retrospective single-center HIPAA-compliant study was approved by the institutional review board, with waiver of informed consent. Four renal compartments inserted into torso phantoms were filled with saline to simulate the unenhanced state and with iodinated solutions to simulate the three levels of renal parenchyma enhancement (140, 180, and 240 HU). Saline-filled spheres simulating renal cysts (15 and 18 mm in diameter) were serially suspended in the renal compartments and imaged with dual-energy and single-energy multi-detector row CT at four different energy levels (80, 100, 120, and 140 kVp). In addition, 28 patients (mean age, 66 years ± 10; mean body mass index, 31.3 kg/m(2) ± 6.2) with 34 intrarenal cysts were included. Virtual monochromatic images were reconstructed in 10-keV increments at energy levels ranging from 40 to 140 keV. Phantom and clinical data were analyzed by using multivariate regression analysis. RESULTS: In the phantom experiment, all polychromatic image data sets showed pseudoenhancement (postcontrast attenuation increase >10 HU) in all investigated conditions, with a significant effect on cyst size (P <.001), location (P <.001), and renal background attenuation level (P <.001). Virtual monochromatic images at energy levels ranging from 80 to 140 keV did not show pseudoenhancement, with the minimum attenuation increase (mean, 6.1 HU ± 1.6; range, 1.6-7.7 HU) on 80-keV images. In patients, pseudoenhancement never occurred on virtual monochromatic images at energy levels ranging from 90 to 140 keV. Patient body size had a significant effect (P = .007) on selection of the optimal monochromatic energy level. CONCLUSION: Dual-energy multi-detector row CT with reconstruction of virtual monochromatic images at an optimal energy level can overcome renal cyst pseudoenhancement.

Authors
Mileto, A; Nelson, RC; Samei, E; Jaffe, TA; Paulson, EK; Barina, A; Choudhury, KR; Wilson, JM; Marin, D
MLA Citation
Mileto, A, Nelson, RC, Samei, E, Jaffe, TA, Paulson, EK, Barina, A, Choudhury, KR, Wilson, JM, and Marin, D. "Impact of dual-energy multi-detector row CT with virtual monochromatic imaging on renal cyst pseudoenhancement: in vitro and in vivo study." Radiology 272.3 (September 2014): 767-776.
PMID
24844472
Source
epmc
Published In
Radiology
Volume
272
Issue
3
Publish Date
2014
Start Page
767
End Page
776
DOI
10.1148/radiol.14132856

An X-ray scatter system for material identification in cluttered objects: A Monte Carlo simulation study

Authors
Lakshmanan, MN; Kapadia, AJ; Sahbaee, P; Wolter, SD; Harrawood, BP; Brady, D; Samei, E
MLA Citation
Lakshmanan, MN, Kapadia, AJ, Sahbaee, P, Wolter, SD, Harrawood, BP, Brady, D, and Samei, E. "An X-ray scatter system for material identification in cluttered objects: A Monte Carlo simulation study." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 335 (September 2014): 31-38.
Source
crossref
Published In
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
Volume
335
Publish Date
2014
Start Page
31
End Page
38
DOI
10.1016/j.nimb.2014.05.021

Quantum noise properties of CT images with anatomical textured backgrounds across reconstruction algorithms: FBP and SAFIRE.

Quantum noise properties of CT images are generally assessed using simple geometric phantoms with uniform backgrounds. Such phantoms may be inadequate when assessing nonlinear reconstruction or postprocessing algorithms. The purpose of this study was to design anatomically informed textured phantoms and use the phantoms to assess quantum noise properties across two clinically available reconstruction algorithms, filtered back projection (FBP) and sinogram affirmed iterative reconstruction (SAFIRE).Two phantoms were designed to represent lung and soft-tissue textures. The lung phantom included intricate vessel-like structures along with embedded nodules (spherical, lobulated, and spiculated). The soft tissue phantom was designed based on a three-dimensional clustered lumpy background with included low-contrast lesions (spherical and anthropomorphic). The phantoms were built using rapid prototyping (3D printing) technology and, along with a uniform phantom of similar size, were imaged on a Siemens SOMATOM Definition Flash CT scanner and reconstructed with FBP and SAFIRE. Fifty repeated acquisitions were acquired for each background type and noise was assessed by estimating pixel-value statistics, such as standard deviation (i.e., noise magnitude), autocorrelation, and noise power spectrum. Noise stationarity was also assessed by examining the spatial distribution of noise magnitude. The noise properties were compared across background types and between the two reconstruction algorithms.In FBP and SAFIRE images, noise was globally nonstationary for all phantoms. In FBP images of all phantoms, and in SAFIRE images of the uniform phantom, noise appeared to be locally stationary (within a reasonably small region of interest). Noise was locally nonstationary in SAFIRE images of the textured phantoms with edge pixels showing higher noise magnitude compared to pixels in more homogenous regions. For pixels in uniform regions, noise magnitude was reduced by an average of 60% in SAFIRE images compared to FBP. However, for edge pixels, noise magnitude ranged from 20% higher to 40% lower in SAFIRE images compared to FBP. SAFIRE images of the lung phantom exhibited distinct regions with varying noise texture (i.e., noise autocorrelation/power spectra).Quantum noise properties observed in uniform phantoms may not be representative of those in actual patients for nonlinear reconstruction algorithms. Anatomical texture should be considered when evaluating the performance of CT systems that use such nonlinear algorithms.

Authors
Solomon, J; Samei, E
MLA Citation
Solomon, J, and Samei, E. "Quantum noise properties of CT images with anatomical textured backgrounds across reconstruction algorithms: FBP and SAFIRE." Medical physics 41.9 (September 2014): 091908-.
PMID
25186395
Source
epmc
Published In
Medical physics
Volume
41
Issue
9
Publish Date
2014
Start Page
091908
DOI
10.1118/1.4893497

Dose index analytics: more than a low number.

Authors
Samei, E; Christianson, O
MLA Citation
Samei, E, and Christianson, O. "Dose index analytics: more than a low number." Journal of the American College of Radiology : JACR 11.8 (August 2014): 832-834.
PMID
24996295
Source
epmc
Published In
Journal of the American College of Radiology
Volume
11
Issue
8
Publish Date
2014
Start Page
832
End Page
834
DOI
10.1016/j.jacr.2014.05.004

Model-based CT performance assessment and optimization for iodinated and noniodinated imaging tasks as a function of kVp and body size.

The goal of this study was to assess the comparative performance of iterative reconstruction in space (IRIS) and filtered back projection (FBP) reconstruction algorithms in terms of image quality and dose across kVps and phantom sizes.The ACR CT phantom (model 464) was supplemented with the addition of an iodinated spherical capsule (1.5 mm diameter, 3.4 mg iodine per ml) to simulate the contrast filled structures and with an additional circular attachment consisting of an array of 500 um brass beads for spatial resolution measurements. A larger sized phantom was also created by wrapping the original phantom with additional tissue equivalent material of 4 cm thickness. The phantoms were imaged on a 64 detector array multidetector computed tomography scanner (Somatom Definition, Siemens, Germany) using clinically applicable protocols (0.5 s rotation time; 80, 100, 120, and 140 kVp; 64 to 640 mA; 220 to 250 mm field of view). Images were reconstructed using the FBP and the IRIS algorithms. Combining measurements of image noise and spatial resolution with a task function, a figure of merit (FOM) for image quality was generated taking into account the type of visualization required from the image for the detection of either large or small image features with and without iodine content. The FOM was further reported in terms of area under the receiver operating characteristic (ROC) curve (AZ) to predict the comparative diagnostic performance of the two algorithms at different dose levels.For a given dose level, the predicted AZ for IRIS consistently outperformed that of FBP. At comparative AZ, depending on protocol and task, the dose requirement for the optimal technique (optimized kVp with IRIS) was 2-3 times lower than that for standard technique (120 kVp with FBP). The potential for dose reduction was found to be higher when performing small feature detection tasks in comparison to larger feature detection tasks. The optimal kVp was from 80 to 100 kVp for the small phantom, 100 to 120 kVp for the larger phantom.Overall, greater dose reduction may be achieved with IRIS compared to FBP, with enhanced advantage at thinner slice reconstructions. The results highlight how IRIS may offer a superior balance between image quality and dose across a range of imaging tasks, thus enabling dose reduction at constant quality or image quality improvement at constant dose. The prediction of the investigation can be used toward effective design of subsequent clinical studies.

Authors
Samei, E; Richard, S; Lurwitz, L
MLA Citation
Samei, E, Richard, S, and Lurwitz, L. "Model-based CT performance assessment and optimization for iodinated and noniodinated imaging tasks as a function of kVp and body size." Medical physics 41.8 (August 2014): 081910-.
PMID
25086541
Source
epmc
Published In
Medical physics
Volume
41
Issue
8
Publish Date
2014
Start Page
081910
DOI
10.1118/1.4890082

The impact on CT dose of the variability in tube current modulation technology: a theoretical investigation.

Body CT scans are routinely performed using tube-current-modulation (TCM) technology. There is notable variability across CT manufacturers in terms of how TCM technology is implemented. Some manufacturers aim to provide uniform image noise across body regions and patient sizes, whereas others aim to provide lower noise for smaller patients. The purpose of this study was to conduct a theoretical investigation to understand how manufacturer-dependent TCM scheme affects organ dose, and to develop a generic approach for assessing organ dose across TCM schemes. The adult reference female extended cardiac-torso (XCAT) phantom was used for this study. A ray-tracing method was developed to calculate the attenuation of the phantom for a given projection angle based on phantom anatomy, CT system geometry, x-ray energy spectrum, and bowtie filter filtration. The tube current (mA) for a given projection angle was then calculated as a log-linear function of the attenuation along that projection. The slope of this function, termed modulation control strength, α, was varied from 0 to 1 to emulate the variability in TCM technology. Using a validated Monte Carlo program, organ dose was simulated for five α values (α = 0, 0.25, 0.5, 0.75, and 1) in the absence and presence of a realistic system mA limit. Organ dose was further normalized by volume-weighted CT dose index (CTDIvol) to obtain conversion factors (h factors) that are relatively independent of system specifics and scan parameters. For both chest and abdomen-pelvis scans and for 24 radiosensitive organs, organ dose conversion factors varied with α, following second-order polynomial equations. This result suggested the need for α-specific organ dose conversion factors (i.e., conversion factors specific to the modulation scheme used). On the other hand, across the full range of α values, organ dose in a TCM scan could be derived from the conversion factors established for a fixed-mA scan (hFIXED). This was possible by multiplying hFIXED by a revised definition of CTDIvol that accounts for two factors: (a) the tube currents at the location of an organ and (b) the variation in organ volume along the longitudinal direction. This α-generic approach represents an approximation. The error associated with this approximation was evaluated using the α-specific organ dose (i.e., the organ dose obtained by using α-specific mA profiles as inputs into the Monte Carlo simulation) as the reference standard. When the mA profiles were constrained by a realistic system limit, this α-generic approach had errors of less than ~20% for the full range of α values. This was the case for 24 radiosensitive organs in both chest and abdomen-pelvis CT scans with the exception of thyroid in the chest scan and bladder in the abdomen-pelvis scan. For these two organs, the errors were less than ~40%. The results of this theoretical study suggested that knowing the mA modulation profile and the fixed-mA conversion factors, organ dose may be estimated for a TCM scan independent of the specific modulation scheme applied.

Authors
Li, X; Segars, WP; Samei, E
MLA Citation
Li, X, Segars, WP, and Samei, E. "The impact on CT dose of the variability in tube current modulation technology: a theoretical investigation." Physics in medicine and biology 59.16 (August 2014): 4525-4548.
PMID
25069102
Source
epmc
Published In
Physics in Medicine and Biology
Volume
59
Issue
16
Publish Date
2014
Start Page
4525
End Page
4548
DOI
10.1088/0031-9155/59/16/4525

Development and application of a suite of 4-D virtual breast phantoms for optimization and evaluation of breast imaging systems.

Mammography is currently the most widely utilized tool for detection and diagnosis of breast cancer. However, in women with dense breast tissue, tissue overlap may obscure lesions. Digital breast tomosynthesis can reduce tissue overlap. Furthermore, imaging with contrast enhancement can provide additional functional information about lesions, such as morphology and kinetics, which in turn may improve lesion identification and characterization. The performance of these imaging techniques is strongly dependent on the structural composition of the breast, which varies significantly among patients. Therefore, imaging system and imaging technique optimization should take patient variability into consideration. Furthermore, optimization of imaging techniques that employ contrast agents should include the temporally varying breast composition with respect to the contrast agent uptake kinetics. To these ends, we have developed a suite of 4-D virtual breast phantoms, which are incorporated with the kinetics of contrast agent propagation in different tissues and can realistically model normal breast parenchyma as well as benign and malignant lesions. This development presents a new approach in performing simulation studies using truly anthropomorphic models. To demonstrate the utility of the proposed 4-D phantoms, we present a simplified example study to compare the performance of 14 imaging paradigms qualitatively and quantitatively.

Authors
Kiarashi, N; Lo, JY; Lin, Y; Ikejimba, LC; Ghate, SV; Nolte, LW; Dobbins, JT; Segars, WP; Samei, E
MLA Citation
Kiarashi, N, Lo, JY, Lin, Y, Ikejimba, LC, Ghate, SV, Nolte, LW, Dobbins, JT, Segars, WP, and Samei, E. "Development and application of a suite of 4-D virtual breast phantoms for optimization and evaluation of breast imaging systems." IEEE transactions on medical imaging 33.7 (July 2014): 1401-1409.
PMID
24691118
Source
epmc
Published In
IEEE Transactions on Medical Imaging
Volume
33
Issue
7
Publish Date
2014
Start Page
1401
End Page
1409
DOI
10.1109/tmi.2014.2312733

Patient-based estimation of organ dose for a population of 58 adult patients across 13 protocol categories.

This study aimed to provide a comprehensive patient-specific organ dose estimation across a multiplicity of computed tomography (CT) examination protocols.A validated Monte Carlo program was employed to model a common CT system (LightSpeed VCT, GE Healthcare). The organ and effective doses were estimated from 13 commonly used body and neurological CT examination. The dose estimation was performed on 58 adult computational extended cardiac-torso phantoms (35 male, 23 female, mean age 51.5 years, mean weight 80.2 kg). The organ dose normalized by CTDIvol (h factor) and effective dose normalized by the dose length product (DLP) (k factor) were calculated from the results. A mathematical model was derived for the correlation between the h and k factors with the patient size across the protocols. Based on this mathematical model, a dose estimation iPhone operating system application was designed and developed to be used as a tool to estimate dose to the patients for a variety of routinely used CT examinations.The organ dose results across all the protocols showed an exponential decrease with patient body size. The correlation was generally strong for the organs which were fully or partially located inside the scan coverage (Pearson sample correlation coefficient (r) of 0.49). The correlation was weaker for organs outside the scan coverage for which distance between the organ and the irradiation area was a stronger predictor of dose to the organ. For body protocols, the effective dose before and after normalization by DLP decreased exponentially with increasing patient's body diameter (r > 0.85). The exponential relationship between effective dose and patient's body diameter was significantly weaker for neurological protocols (r < 0.41), where the trunk length was a slightly stronger predictor of effective dose (0.15 < r < 0.46).While the most accurate estimation of a patient dose requires specific modeling of the patient anatomy, a first order approximation of organ and effective doses from routine CT scan protocols can be reasonably estimated using size specific factors. Estimation accuracy is generally poor for organ outside the scan range and for neurological protocols. The dose calculator designed in this study can be used to conveniently estimate and report the dose values for a patient across a multiplicity of CT scan protocols.

Authors
Sahbaee, P; Segars, WP; Samei, E
MLA Citation
Sahbaee, P, Segars, WP, and Samei, E. "Patient-based estimation of organ dose for a population of 58 adult patients across 13 protocol categories." Medical physics 41.7 (July 2014): 072104-.
PMID
24989399
Source
epmc
Published In
Medical physics
Volume
41
Issue
7
Publish Date
2014
Start Page
072104
DOI
10.1118/1.4883778

Assessment of volumetric noise and resolution performance for linear and nonlinear CT reconstruction methods.

For nonlinear iterative image reconstructions (IR), the computed tomography (CT) noise and resolution properties can depend on the specific imaging conditions, such as lesion contrast and image noise level. Therefore, it is imperative to develop a reliable method to measure the noise and resolution properties under clinically relevant conditions. This study aimed to develop a robust methodology to measure the three-dimensional CT noise and resolution properties under such conditions and to provide guidelines to achieve desirable levels of accuracy and precision.The methodology was developed based on a previously reported CT image quality phantom. In this methodology, CT noise properties are measured in the uniform region of the phantom in terms of a task-based 3D noise-power spectrum (NPStask). The in-plane resolution properties are measured in terms of the task transfer function (TTF) by applying a radial edge technique to the rod inserts in the phantom. The z-direction resolution properties are measured from a supplemental phantom, also in terms of the TTF. To account for the possible nonlinearity of IR, the NPStask is measured with respect to the noise magnitude, and the TTF with respect to noise magnitude and edge contrast. To determine the accuracy and precision of the methodology, images of known noise and resolution properties were simulated. The NPStask and TTF were measured on the simulated images and compared to the truth, with criteria established to achieve NPStask and TTF measurements with <10% error. To demonstrate the utility of this methodology, measurements were performed on a commercial CT system using five dose levels, two slice thicknesses, and three reconstruction algorithms (filtered backprojection, FBP; iterative reconstruction in imaging space, IRIS; and sinogram affirmed iterative reconstruction with strengths of 5, SAFIRE5).To achieve NPStask measurements with <10% error, the number of regions of interest needed to be greater than 65. To achieve TTF measurements with <10% error, the contrast-to-noise ratio of the edge needed to be ≥15, achievable by averaging multiple slices across the same edge. The NPStask measured on a commercial CT system showed IR's reduced noise (IRIS, 30% and SAFIRE5, 55%) and "waxier" texture (peak frequencies: FBP, 0.25 mm(-1); IRIS, 0.23 mm(-1); and SAFIRE5, 0.16 mm(-1)). The TTF measured within the axial plane showed improved in-plane resolution with SAFIRE5 at the TTF 50% frequency, f50 (FBP, 0.36-0.41 mm(-1); SAFIRE5, 0.37-0.46 mm(-1)). The TTF measured along the axial direction showed improved z-direction resolution with thinner slice thickness (f50: 0.6 mm, 0.35-0.79 mm(-1); 1.5 mm, 0.22-0.3 mm(-1)) and with SAFIRE5 (f50: FBP, 0.35-0.52 mm(-1); SAFIRE5, 0.42-0.79 mm(-1)). Both in-plane and z-direction resolution of SAFIRE5 showed strong dependency on contrast, reflecting SAFIRE5's nonlinearity.A methodology was developed to measure three-dimensional CT noise and resolution properties for iterative reconstruction, especially at challenging measurement conditions with low contrast and high image noise. The methodology also demonstrated its utility for evaluating commercial CT systems.

Authors
Chen, B; Christianson, O; Wilson, JM; Samei, E
MLA Citation
Chen, B, Christianson, O, Wilson, JM, and Samei, E. "Assessment of volumetric noise and resolution performance for linear and nonlinear CT reconstruction methods." Medical physics 41.7 (July 2014): 071909-.
PMID
24989387
Source
epmc
Published In
Medical physics
Volume
41
Issue
7
Publish Date
2014
Start Page
071909
DOI
10.1118/1.4881519

An angle-dependent estimation of CT x-ray spectrum from rotational transmission measurements.

Computed tomography (CT) performance as well as dose and image quality is directly affected by the x-ray spectrum. However, the current assessment approaches of the CT x-ray spectrum require costly measurement equipment and complicated operational procedures, and are often limited to the spectrum corresponding to the center of rotation. In order to address these limitations, the authors propose an angle-dependent estimation technique, where the incident spectra across a wide range of angular trajectories can be estimated accurately with only a single phantom and a single axial scan in the absence of the knowledge of the bowtie filter.The proposed technique uses a uniform cylindrical phantom, made of ultra-high-molecular-weight polyethylene and positioned in an off-centered geometry. The projection data acquired with an axial scan have a twofold purpose. First, they serve as a reflection of the transmission measurements across different angular trajectories. Second, they are used to reconstruct the cross sectional image of the phantom, which is then utilized to compute the intersection length of each transmission measurement. With each CT detector element recording a range of transmission measurements for a single angular trajectory, the spectrum is estimated for that trajectory. A data conditioning procedure is used to combine information from hundreds of collected transmission measurements to accelerate the estimation speed, to reduce noise, and to improve estimation stability. The proposed spectral estimation technique was validated experimentally using a clinical scanner (Somatom Definition Flash, Siemens Healthcare, Germany) with spectra provided by the manufacturer serving as the comparison standard. Results obtained with the proposed technique were compared against those obtained from a second conventional transmission measurement technique with two materials (i.e., Cu and Al). After validation, the proposed technique was applied to measure spectra from the clinical system across a range of angular trajectories [-15°, 15°] and spectrum settings (80, 100, 120, 140 kVp).At 140 kVp, the proposed technique was comparable to the conventional technique in terms of the mean energy difference (MED, -0.29 keV) and the normalized root mean square difference (NRMSD, 0.84%) from the comparison standard compared to 0.64 keV and 1.56%, respectively, with the conventional technique. The average absolute MEDs and NRMSDs across kVp settings and angular trajectories were less than 0.61 keV and 3.41%, respectively, which indicates a high level of estimation accuracy and stability.An angle-dependent estimation technique of CT x-ray spectra from rotational transmission measurements was proposed. Compared with the conventional technique, the proposed method simplifies the measurement procedures and enables incident spectral estimation for a wide range of angular trajectories. The proposed technique is suitable for rigorous research objectives as well as routine clinical quality control procedures.

Authors
Lin, Y; Ramirez-Giraldo, JC; Gauthier, DJ; Stierstorfer, K; Samei, E
MLA Citation
Lin, Y, Ramirez-Giraldo, JC, Gauthier, DJ, Stierstorfer, K, and Samei, E. "An angle-dependent estimation of CT x-ray spectrum from rotational transmission measurements." Medical physics 41.6 (June 2014): 062104-.
PMID
24877831
Source
epmc
Published In
Medical physics
Volume
41
Issue
6
Publish Date
2014
Start Page
062104
DOI
10.1118/1.4876380

WE-D-18A-02: Performance Evaluation of Automatic Exposure Control (AEC) Across 12 Clinical CT Systems.

Automatic exposure control (AEC) is not typically evaluated or monitored in CT quality assurance programs. The purpose of this study was to develop/evaluate a new AEC testing platform for the clinical physics program at our institution, and characterize AEC performance across different CT systems.The Mercury Phantom comprises three tapered and four uniform regions of polyethylene(16, 23, 30, and 37 cm in diameter); each region includes four inserts: air, Polystyrene, Acrylic, and Teflon. The phantom was imaged using AEC and a fixed tube current technique across 12 clinical CT scanners. Those included five Siemens Somatom Definition Flash, four GE Discovery CT750HD, and three GE Lightspeed VCT systems. A custom MATLAB software package provided MTF, NPS, and detectability indices for each diameter section of the phantom. Detectability indices were used to evaluate the relationship between AEC setting, patient size, and image quality. The magnitude of the power of a best fit exponential curve to the detectability indices and phantom diameter was used as a measure of AEC strength. Results were compared within/across scanner models, and as baseline values for comparison with future system performance testing.For each scanner model, the percent difference in expected image quality and AEC setting was under 3%(+/-2%). The average decrease in detectability between the small and large diameter phantom sections for the Siemens Flash, GE CT750, and GE VCT was 99%(+/-10%), 42%(+/-25%), and 33%(+/-41%), respectively. The value signifying AEC strength was 0.051(+/-13%), 0.019(+/-18%), and 0.018(+/-26%), for the Siemens Flash, GE CT750, and GE VCT models, respectively.This study demonstrated a practical approach to test the AEC performance of clinical CT systems at a large academic medical center. The quantification and evaluation of AEC performance should be included in acceptance testing and in annual physics testing of clinical CT systems.

Authors
Winslow, J; Wilson, J; Christianson, O; Samei, E
MLA Citation
Winslow, J, Wilson, J, Christianson, O, and Samei, E. "WE-D-18A-02: Performance Evaluation of Automatic Exposure Control (AEC) Across 12 Clinical CT Systems." Medical physics 41.6 (June 2014): 498-.
PMID
28036597
Source
epmc
Published In
Medical physics
Volume
41
Issue
6
Publish Date
2014
Start Page
498
DOI
10.1118/1.4889411

SU-E-I-94: Automated Image Quality Assessment of Radiographic Systems Using An Anthropomorphic Phantom.

In a large, academic medical center, consistent radiographic imaging performance is difficult to routinely monitor and maintain, especially for a fleet consisting of multiple vendors, models, software versions, and numerous imaging protocols. Thus, an automated image quality control methodology has been implemented using routine image quality assessment with a physical, stylized anthropomorphic chest phantom.The "Duke" Phantom (Digital Phantom 07-646, Supertech, Elkhart, IN) was imaged twice on each of 13 radiographic units from a variety of vendors at 13 primary care clinics. The first acquisition used the clinical PA chest protocol to acquire the post-processed "FOR PRESENTATION" image. The second image was acquired without an antiscatter grid followed by collection of the "FOR PROCESSING" image. Manual CNR measurements were made from the largest and thickest contrast-detail inserts in the lung, heart, and abdominal regions of the phantom in each image. An automated image registration algorithm was used to estimate the CNR of the same insert using similar ROIs. Automated measurements were then compared to the manual measurements.Automatic and manual CNR measurements obtained from "FOR PRESENTATION" images had average percent differences of 0.42%±5.18%, -3.44%±4.85%, and 1.04%±3.15% in the lung, heart, and abdominal regions, respectively; measurements obtained from "FOR PROCESSING" images had average percent differences of -0.63%±6.66%, -0.97%±3.92%, and -0.53%±4.18%, respectively. The maximum absolute difference in CNR was 15.78%, 10.89%, and 8.73% in the respective regions. In addition to CNR assessment of the largest and thickest contrast-detail inserts, the automated method also provided CNR estimates for all 75 contrast-detail inserts in each phantom image.Automated analysis of a radiographic phantom has been shown to be a fast, robust, and objective means for assessing radiographic image quality. The method reduces the burden of manual measurements and provides a means by which to monitor and compare radiographic system performance.

Authors
Wells, J; Wilson, J; Zhang, Y; Samei, E; Ravin, CE
MLA Citation
Wells, J, Wilson, J, Zhang, Y, Samei, E, and Ravin, CE. "SU-E-I-94: Automated Image Quality Assessment of Radiographic Systems Using An Anthropomorphic Phantom." Medical physics 41.6 (June 2014): 152-.
PMID
28037302
Source
epmc
Published In
Medical physics
Volume
41
Issue
6
Publish Date
2014
Start Page
152
DOI
10.1118/1.4888044

SU-C-9A-02: Structured Noise Index as An Automated Quality Control for Nuclear Medicine: A Two Year Experience.

Flood-field uniformity evaluation is an essential element in the assessment of nuclear medicine (NM) gamma cameras. It serves as the central element of the quality control (QC) program, acquired and analyzed on a daily basis prior to clinical imaging. Uniformity images are traditionally analyzed using pixel value-based metrics which often fail to capture subtle structure and patterns caused by changes in gamma camera performance requiring additional visual inspection which is subjective and time demanding. The goal of this project was to develop and implement a robust QC metrology for NM that is effective in identifying non-uniformity issues, reporting issues in a timely manner for efficient correction prior to clinical involvement, all incorporated into an automated effortless workflow, and to characterize the program over a two year period.A new quantitative uniformity analysis metric was developed based on 2D noise power spectrum metrology and confirmed based on expert observer visual analysis. The metric, termed Structured Noise Index (SNI) was then integrated into an automated program to analyze, archive, and report on daily NM QC uniformity images. The effectiveness of the program was evaluated over a period of 2 years.The SNI metric successfully identified visually apparent non-uniformities overlooked by the pixel valuebased analysis methods. Implementation of the program has resulted in nonuniformity identification in about 12% of daily flood images. In addition, due to the vigilance of staff response, the percentage of days exceeding trigger value shows a decline over time.The SNI provides a robust quantification of the NM performance of gamma camera uniformity. It operates seamlessly across a fleet of multiple camera models. The automated process provides effective workflow within the NM spectra between physicist, technologist, and clinical engineer. The reliability of this process has made it the preferred platform for NM uniformity analysis.

Authors
Nelson, J; Christianson, O; Samei, E
MLA Citation
Nelson, J, Christianson, O, and Samei, E. "SU-C-9A-02: Structured Noise Index as An Automated Quality Control for Nuclear Medicine: A Two Year Experience." Medical physics 41.6 (June 2014): 104-.
PMID
28037709
Source
epmc
Published In
Medical physics
Volume
41
Issue
6
Publish Date
2014
Start Page
104
DOI
10.1118/1.4887843

SU-F-18C-07: Automated CT QC Program with Analytics, Archival, and Notification Capabilities.

Tracking metrics over time is a well-established means of establishing a quality control program. The number of metrics followed and testing frequency is limited by available resources. Automating the image analysis and data archival of a QC program enables objective and efficient tracking of performance metrics. The purpose of this study was to develop such a QC method and to assess its utility at a large clinical facility.The QC program at our institution is based on the acquisition of daily water-phantom scans, and biweekly ACR-phantom scans for each CT system. We developed a QC program to analyze these data. The QC software operates on the images sent directly to our server. The relevant information from DICOM headers was extracted, data analyzed, and a database was populated. The measurements performed on the waterphantom included water CT-number, uniformity, noise, and artifact. The measurements performed on the ACR-phantom included the MTF, NPS, detectability, artifact, uniformity, CNR, and the CT-numbers for water, polyethylene, bone, air, and acrylic. Email notifications and criteria limits were directly based upon ACR accreditation requirements and developing threshold values.Across ten clinical CT scanners, the daily water CT-number was -0.2+/-1.4 HU(mean+/-standard deviation). The corresponding numbers for 10%MTF, uniformity, CNR squared normalized to CTDI, and detectability squared normalized to CTDI were 0.69+/-0.01 (1/mm), 0.93+/-0.29, 0.06+/-0.02 (1/mGy), and 3.3+/-0.7 (1/mGy), respectively. For all ACR-phantom inserts, the largest standard deviation for any individual scanner was 1.9 HU. Artifact analysis triggers successfully identified problematic images.Automating image analysis allows one to frequently track meaningful metrics that would be impractical to follow otherwise. System inconsistencies are more likely to be identified and corrected earlier. Much tighter system specific criteria limits are possible.

Authors
Winslow, J; Christianson, O; Samei, E
MLA Citation
Winslow, J, Christianson, O, and Samei, E. "SU-F-18C-07: Automated CT QC Program with Analytics, Archival, and Notification Capabilities." Medical physics 41.6 (June 2014): 404-.
PMID
28038307
Source
epmc
Published In
Medical physics
Volume
41
Issue
6
Publish Date
2014
Start Page
404
DOI
10.1118/1.4889092

TH-E-9A-01: Medical Physics 1.0 to 2.0, Session 4: Computed Tomography, Ultrasound and Nuclear Medicine.

Medical Physics 2.0 is a bold vision for an existential transition of clinical imaging physics in face of the new realities of value-based and evidencebased medicine, comparative effectiveness, and meaningful use. It speaks to how clinical imaging physics can expand beyond traditional insular models of inspection and acceptance testing, oriented toward compliance, towards team-based models of operational engagement, prospective definition and assurance of effective use, and retrospective evaluation of clinical performance. Organized into four sessions of the AAPM, this particular session focuses on three specific modalities as outlined below. CT 2.0: CT has been undergoing a dramatic transition in the last few decades. While the changes in the technology merits discussions of their own, an important question is how clinical medical physicists are expected to effectively engage with the new realities of CT technology and practice. Consistent with the upcoming paradigm of Medical Physics 2.0, this CT presentation aims to provide definitions and demonstration of the components of the new clinical medical physics practice pertaining CT. The topics covered include physics metrics and analytics that aim to provide higher order clinicallyrelevant quantification of system performance as pertains to new (and not so new) technologies. That will include the new radiation and dose metrics (SSDE, organ dose, risk indices), image quality metrology (MTF/NPS/d'), task-based phantoms, and the effect of patient size. That will follow with a discussion of the testing implication of new CT hardware (detectors, tubes), acquisition methods (innovative helical geometries, AEC, wide beam CT, dual energy, inverse geometry, application specialties), and image processing and analysis (iterative reconstructions, quantitative CT, advanced renditions). The presentation will conclude with a discussion of clinical and operational aspects of Medical Physics 2.0 including training and communication, use optimization (dose and technique factors), automated analysis and data management (automated QC methods, protocol tracking, dose monitoring, issue tracking), and meaningful QC considerations. US 2.0: Ultrasound imaging is evolving at a rapid pace, adding new imaging functions and modes that continue to enhance its clinical utility and benefits to patients. The ultrasound talk will look ahead 10-15 years and consider how medical physicists can bring maximal value to the clinical ultrasound practices of the future. The roles of physics in accreditation and regulatory compliance, image quality and exam optimization, clinical innovation, and education of staff and trainees will all be considered. A detailed examination of expected technology evolution and impact on image quality metrics will be presented. Clinical implementation of comprehensive physics services will also be discussed. Nuclear Medicine 2.0: Although the basic science of nuclear imaging has remained relatively unchanged since its inception, advances in instrumentation continue to advance the field into new territories. With a great number of these advances occurring over the past decade, the role and testing strategies of clinical nuclear medicine physicists must evolve in parallel. The Nuclear Medicine 2.0 presentation is designed to highlight some of the recent advances from a clinical medical physicist perspective and provide ideas and motivation for designing better evaluation strategies. Topics include improvement of traditional physics metrics and analytics, testing implications of hybrid imaging and advanced detector technologies, and strategies for effective implementation into the clinic.1. Become familiar with new physics metrics and analytics in nuclear medicine, CT, and ultrasound. 2. To become familiar with the major new developments of clinical physics support. 3. To understand the physics testing implications of new technologies, hardware, software, and applications. 4. Identify approaches for implementing comprehensive medical physics services in future imaging practices.

Authors
Samei, E; Hangiandreou, N; Nelson, J
MLA Citation
Samei, E, Hangiandreou, N, and Nelson, J. "TH-E-9A-01: Medical Physics 1.0 to 2.0, Session 4: Computed Tomography, Ultrasound and Nuclear Medicine." Medical physics 41.6 (June 2014): 574-575.
PMID
28037388
Source
epmc
Published In
Medical physics
Volume
41
Issue
6
Publish Date
2014
Start Page
574
End Page
575
DOI
10.1118/1.4889842

TU-C-18C-01: Medical Physics 1.0 to 2.0: Introduction and Panel Discussion.

Medical Physics 2.0, a new frontier in clinical imaging physics: Diagnostic imaging has always been a technological highlight of modern medicine. Imaging systems, with their ever-expanding advancement in terms of technology and application, increasingly require skilled expertise to understand the delicacy of their operation, monitor their performance, design their effective use, and ensure their overall quality and safety, scientifically and in quantitative terms. Physicists can play a crucial role in that process. But that role has largely remained a severely untapped resource. Many imaging centers fail to appreciate this potential, with medical physics groups either nonexistent or highly understaffed and their services poorly integrated into the patient care process. As a field, we have yet to define and enact how the clinical physicist can engage as an active, effective, and integral member of the clinical team, and how the services that she/he provides can be financially accounted for. Physicists do and will always contribute to research and development. However, their indispensible contribution to clinical imaging operations is something that has not been adequately established. That, in conjunction with new realities of healthcare practice, indicates a growing need to establish an updated approach to clinical medical imaging physics. This presentation aims to describe a vision as how clinical imaging physics can expand beyond traditional insular models of inspection and acceptance testing, oriented toward compliance, towards team-based models of operational engagement addressing topics such as new non-classical challenges of new technologies, quantitative imaging, and operational optimization. The Medical Physics 2.0 paradigm extends clinical medical physics from isolated characterization of inherent properties of the equipment to effective use of the equipment and to retrospective evaluation of clinical performance. This is an existential transition of the field that speaks to the new paradigms of value-based and evidence-based medicine, comparative effectiveness, and meaningful use. The panel discussion that follows includes prominent practitioners, thinkers, and leaders that would lead the discussion on how Medical Physics 2.0 can be actualized. Topics of discussion will include the administrative, financial, regulatory, and accreditation requirements of the new paradigm, effective models of practice, and the steps that we need to take to make MP 2.0 a reality.1. To understand the new paradigm of clinical medical physics practice extending from traditional insular models of compliance towards teambased models of operational engagement. 2. To understand how clinical physics can most effectively contribute to clinical care. 3. Learn to identify strengths and weaknesses in studies designed to measure the effect of low doses of ionizing radiation 4. To recognize the impediments to Medical Physics 2.0 paradigm.

Authors
Samei, E; Pfeiffer, D; Frey, G; Krupinski, E; Pizzutiello, R; Carson, P; Mahesh, M; Hangiandreou, N; Jordan, D; Dixon, R
MLA Citation
Samei, E, Pfeiffer, D, Frey, G, Krupinski, E, Pizzutiello, R, Carson, P, Mahesh, M, Hangiandreou, N, Jordan, D, and Dixon, R. "TU-C-18C-01: Medical Physics 1.0 to 2.0: Introduction and Panel Discussion." Medical physics 41.6 (June 2014): 461-462.
PMID
28037344
Source
epmc
Published In
Medical physics
Volume
41
Issue
6
Publish Date
2014
Start Page
461
End Page
462
DOI
10.1118/1.4889289

TH-C-18A-06: Combined CT Image Quality and Radiation Dose Monitoring Program Based On Patient Data to Assess Consistency of Clinical Imaging Across Scanner Models.

One of the principal challenges of clinical imaging is to achieve an ideal balance between image quality and radiation dose across multiple CT models. The number of scanners and protocols at large medical centers necessitates an automated quality assurance program to facilitate this objective. Therefore, the goal of this work was to implement an automated CT image quality and radiation dose monitoring program based on actual patient data and to use this program to assess consistency of protocols across CT scanner models.Patient CT scans are routed to a HIPPA compliant quality assurance server. CTDI, extracted using optical character recognition, and patient size, measured from the localizers, are used to calculate SSDE. A previously validated noise measurement algorithm determines the noise in uniform areas of the image across the scanned anatomy to generate a global noise level (GNL). Using this program, 2358 abdominopelvic scans acquired on three commercial CT scanners were analyzed. Median SSDE and GNL were compared across scanner models and trends in SSDE and GNL with patient size were used to determine the impact of differing automatic exposure control (AEC) algorithms.There was a significant difference in both SSDE and GNL across scanner models (9-33% and 15-35% for SSDE and GNL, respectively). Adjusting all protocols to achieve the same image noise would reduce patient dose by 27-45% depending on scanner model. Additionally, differences in AEC methodologies across vendors resulted in disparate relationships of SSDE and GNL with patient size.The difference in noise across scanner models indicates that protocols are not optimally matched to achieve consistent image quality. Our results indicated substantial possibility for dose reduction while achieving more consistent image appearance. Finally, the difference in AEC methodologies suggests the need for size-specific CT protocols to minimize variability in image quality across CT vendors.

Authors
Christianson, O; Winslow, J; Samei, E
MLA Citation
Christianson, O, Winslow, J, and Samei, E. "TH-C-18A-06: Combined CT Image Quality and Radiation Dose Monitoring Program Based On Patient Data to Assess Consistency of Clinical Imaging Across Scanner Models." Medical physics 41.6 (June 2014): 558-.
PMID
28036973
Source
epmc
Published In
Medical physics
Volume
41
Issue
6
Publish Date
2014
Start Page
558
DOI
10.1118/1.4889630

SU-C-12A-03: The Impact of Contrast Medium On Radiation Dose in CT: A Systematic Evaluation Across 58 Patient Models.

To assess the effect of contrast medium on radiation dose as a function of time via Monte Carlo simulation from the liver CT scan across a library of 5D XCAT models METHODS: A validated Monte Carlo simulation package (PENELOPE) was employed to model a CT system (LightSpeed 64 VCT, GE Healthcare). The radiation dose was estimated from a common abdomen CT examination. The dose estimation was performed on a library of adult extended cardiac-torso (5D XCAT) phantoms (35 male, 23 female, mean age 51.5 years, mean weight 80.2 kg). The 5D XCAT models were created based on patient-specific iodine concentration-time results from our computational contrast medium propagation model for different intravenous injection protocols. To enable a dynamic estimation of radiation dose, each organ in the model was assigned to its own time-concentration curve via the PENELOPE package, material.exe. Using the Monte Carlo, for each scan time point after the injection, 80 million photons were initiated and tracked through the phantoms. Finally, the dose to the liver was tallied from the deposited energy.Monte Carlo simulation results of radiation dose delivered to the liver from the XCAT models indicated up to 30% increase in dose for different time after the administration of contrast medium.The contrast enhancement is employed in over 60% of imaging modalities, which not only remarkably affects the CT image quality, but also increases the radiation dose by as much as 70%. The postinjection multiple acquisition in several enhanced CT protocols, makes the radiation dose increment through the use of contrast medium, an inevitable factor in optimization of these protocols. The relationship between radiation dose and injected contrast medium as a function of time studied in this work allows optimization of contrast administration for vulnerable individuals.

Authors
Sahbaee, P; Samei, E; Segars, W
MLA Citation
Sahbaee, P, Samei, E, and Segars, W. "SU-C-12A-03: The Impact of Contrast Medium On Radiation Dose in CT: A Systematic Evaluation Across 58 Patient Models." Medical physics 41.6 (June 2014): 106-.
PMID
28037200
Source
epmc
Published In
Medical physics
Volume
41
Issue
6
Publish Date
2014
Start Page
106
DOI
10.1118/1.4887851

MO-C-18A-01: Advances in Model-Based 3D Image Reconstruction.

Recent years have seen the emergence of CT image reconstruction techniques that exploit physical models of the imaging system, photon statistics, and even the patient to achieve improved 3D image quality and/or reduction of radiation dose. With numerous advantages in comparison to conventional 3D filtered backprojection, such techniques bring a variety of challenges as well, including: a demanding computational load associated with sophisticated forward models and iterative optimization methods; nonlinearity and nonstationarity in image quality characteristics; a complex dependency on multiple free parameters; and the need to understand how best to incorporate prior information (including patient-specific prior images) within the reconstruction process. The advantages, however, are even greater - for example: improved image quality; reduced dose; robustness to noise and artifacts; task-specific reconstruction protocols; suitability to novel CT imaging platforms and noncircular orbits; and incorporation of known characteristics of the imager and patient that are conventionally discarded. This symposium features experts in 3D image reconstruction, image quality assessment, and the translation of such methods to emerging clinical applications. Dr. Chen will address novel methods for the incorporation of prior information in 3D and 4D CT reconstruction techniques. Dr. Pan will show recent advances in optimization-based reconstruction that enable potential reduction of dose and sampling requirements. Dr. Stayman will describe a "task-based imaging" approach that leverages models of the imaging system and patient in combination with a specification of the imaging task to optimize both the acquisition and reconstruction process. Dr. Samei will describe the development of methods for image quality assessment in such nonlinear reconstruction techniques and the use of these methods to characterize and optimize image quality and dose in a spectrum of clinical applications.1. Learn the general methodologies associated with model-based 3D image reconstruction. 2. Learn the potential advantages in image quality and dose associated with model-based image reconstruction. 3. Learn the challenges associated with computational load and image quality assessment for such reconstruction methods. 4. Learn how imaging task can be incorporated as a means to drive optimal image acquisition and reconstruction techniques. 5. Learn how model-based reconstruction methods can incorporate prior information to improve image quality, ease sampling requirements, and reduce dose.

Authors
Chen, G; Pan, X; Stayman, J; Samei, E
MLA Citation
Chen, G, Pan, X, Stayman, J, and Samei, E. "MO-C-18A-01: Advances in Model-Based 3D Image Reconstruction." Medical physics 41.6 (June 2014): 416-417.
PMID
28036883
Source
epmc
Published In
Medical physics
Volume
41
Issue
6
Publish Date
2014
Start Page
416
End Page
417
DOI
10.1118/1.4889136

SU-E-I-91: Reproducibility in Prescribed Dose in AEC CT Scans Due to Table Height, Patient Size, and Localizer Acquisition Order.

In CT scanners, the automatic exposure control (AEC) tube current prescription depends on the acquired prescan localizer image(s). The purpose of this study was to quantify the effect that table height, patient size, and localizer acquisition order may have on the reproducibility in prescribed dose.Three phantoms were used for this study: the Mercury Phantom (comprises three tapered and four uniform regions of polyethylene 16, 23, 30, and 37 cm in diameter), acrylic sheets, and an adult anthropomorphic phantom. Phantoms were positioned per clinical protocol by our chief CT technologist or broader symmetry. Using a GE Discovery CT750HD scanner, a lateral (LAT) and posterior-anterior (PA) localizer was acquired for each phantom at different table heights. AEC scan acquisitions were prescribed for each combination of phantom, localizer orientation, and table height; the displayed volume CTDI was recorded for each. Results were analyzed versus table height.For the two largest Mercury Phantom section scans based on the PA localizer, the percent change in volume CTDI from ideal were at least 20% lower and 35% greater for table heights 4 cm above and 4 cm below proper centering, respectively. For scans based on the LAT localizer, the percent change in volume CTDI from ideal were no greater than 12% different for 4 cm differences in table height. The properly centered PA and LAT localizer-based volume CTDI values were within 13% of each other.Since uncertainty in vertical patient positioning is inherently greater than lateral positioning and because the variability in dose exceeds any dose penalties incurred, the LAT localizer should be used to precisely and reproducibly deliver the intended amount of radiation prescribed by CT protocols. CT protocols can be adjusted to minimize the expected change in average patient dose.

Authors
Winslow, J; Hurwitz, L; Christianson, O; Samei, E
MLA Citation
Winslow, J, Hurwitz, L, Christianson, O, and Samei, E. "SU-E-I-91: Reproducibility in Prescribed Dose in AEC CT Scans Due to Table Height, Patient Size, and Localizer Acquisition Order." Medical physics 41.6 (June 2014): 151-.
PMID
28036771
Source
epmc
Published In
Medical physics
Volume
41
Issue
6
Publish Date
2014
Start Page
151
DOI
10.1118/1.4888041

MO-E-17A-02: Incorporation of Contrast Medium Dynamics in Anthropomorphic Phantoms: The Advent of 5D XCAT Models.

To develop a unique method to incorporate the dynamics of contrast-medium propagation into the anthropomorphic phantom, to generate a five-dimensional (5D) patient model for multimodality imaging studies.A compartmental model of blood circulation network within the body was embodied into an extended cardiac-torso (4D-XCAT) patient model. To do so, a computational physiologic model of the human cardiovascular system was developed which includes a series of compartments representing heart, vessels, and organs. Patient-specific cardiac output and blood volume were used as inputs influenced by the weight, height, age, and gender of the patient's model. For a given injection protocol and given XCAT model, the contrast-medium transmission within the body was described by a series of mass balance differential equations, the solutions to which provided the contrast enhancement-time curves for each organ; thereby defining the tissue materials including the contrastmedium within the XCAT model. A library of time-dependent organ materials was then defined. Each organ in each voxelized 4D-XCAT phantom was assigned to a corresponding time-varying material to create the 5D-XCAT phantom in which the fifth dimension is blood/contrast-medium within the temporal domain.The model effectively predicts the time-varying concentration behavior of various contrast-medium administration in each organ for different patient models as function of patient size (weight/height) and different injection protocol factors (injection rate and pattern, iodine concentration or volume). The contrast enhanced XCAT patient models was developed based on the concentration of iodine as a function of time after injection.Majority of medical imaging systems take advantage of contrast-medium administration in terms of better image quality, the effect of which was ignored in previous optimization studies. The study enables a comprehensive optimization of contrast administration both in terms of image quality and radiation dose, and can be used in different modalities such as CT, MRI, and ultrasound.

Authors
Sahbaee, P; Samei, E; Segars, W
MLA Citation
Sahbaee, P, Samei, E, and Segars, W. "MO-E-17A-02: Incorporation of Contrast Medium Dynamics in Anthropomorphic Phantoms: The Advent of 5D XCAT Models." Medical physics 41.6 (June 2014): 424-.
PMID
28036850
Source
epmc
Published In
Medical physics
Volume
41
Issue
6
Publish Date
2014
Start Page
424
DOI
10.1118/1.4889154

MO-C-18C-01: Radiation Risks at Level of Few CT Scans: How Real?- Science to Practice.

There are controversies surrounding radiation effects in human population in the range of radiation doses encountered by patients resulting from one to several CT scans. While it is understandable why the effects from low levels of diagnostic radiation are controversial, the situation is complicated by the media which may distort the known facts. There is need to understand the state of science regarding low-level radiation effects and also to understand how to communicate the potential risk with patients, the public and media. This session will seek to come to a consensus in order to speak with one voice to the media and the public. This session will review radiation effects known so far from a variety of exposed groups since the nuclear holocaust, provide clarification where effects are certain and where they are not, at what level extrapolation is the only way and at what level there is weak but agreeable acceptance. We will depict where and why there is agreement among organizations responsible for studying radiation effects, and how to deal with situations where effects are uncertain. Specific focus on radiation effects in children will be provided.Finally, the session will attempt to bridge the communication gap from the science to how to be an effective communicator with patients, parents, and media about ionizing radiation.1. To have a clear understanding about certainties and uncertainties of radiation effects at the level of a few CT scans 2. To understand the results and limitations from 3 major pediatric CT scientific studies on childhood exposures published recently. 3. To understand successful strategies used in risk communication.

Authors
Rehani, M; Samei, E; Morgan, W; Shore, R; Goske, M
MLA Citation
Rehani, M, Samei, E, Morgan, W, Shore, R, and Goske, M. "MO-C-18C-01: Radiation Risks at Level of Few CT Scans: How Real?- Science to Practice." Medical physics 41.6 (June 2014): 417-.
PMID
28036421
Source
epmc
Published In
Medical physics
Volume
41
Issue
6
Publish Date
2014
Start Page
417
DOI
10.1118/1.4889137

SU-F-18C-01: Minimum Detectability Analysis for Comprehensive Sized Based Optimization of Image Quality and Radiation Dose Across CT Protocols.

This work involved a comprehensive modeling of task-based performance of CT across a wide range of protocols. The approach was used for optimization and consistency of dose and image quality within a large multi-vendor clinical facility.150 adult protocols from the Duke University Medical Center were grouped into sub-protocols with similar acquisition characteristics. A size based image quality phantom (Duke Mercury Phantom) was imaged using these sub-protocols for a range of clinically relevant doses on two CT manufacturer platforms (Siemens, GE). The images were analyzed to extract task-based image quality metrics such as the Task Transfer Function (TTF), Noise Power Spectrum, and Az based on designer nodule task functions. The data were analyzed in terms of the detectability of a lesion size/contrast as a function of dose, patient size, and protocol. A graphical user interface (GUI) was developed to predict image quality and dose to achieve a minimum level of detectability.Image quality trends with variations in dose, patient size, and lesion contrast/size were evaluated and calculated data behaved as predicted. The GUI proved effective to predict the Az values representing radiologist confidence for a targeted lesion, patient size, and dose. As an example, an abdomen pelvis exam for the GE scanner, with a task size/contrast of 5-mm/50-HU, and an Az of 0.9 requires a dose of 4.0, 8.9, and 16.9 mGy for patient diameters of 25, 30, and 35 cm, respectively. For a constant patient diameter of 30 cm, the minimum detected lesion size at those dose levels would be 8.4, 5, and 3.9 mm, respectively.The designed CT protocol optimization platform can be used to evaluate minimum detectability across dose levels and patient diameters. The method can be used to improve individual protocols as well as to improve protocol consistency across CT scanners.

Authors
Smitherman, C; Chen, B; Samei, E
MLA Citation
Smitherman, C, Chen, B, and Samei, E. "SU-F-18C-01: Minimum Detectability Analysis for Comprehensive Sized Based Optimization of Image Quality and Radiation Dose Across CT Protocols." Medical physics 41.6 (June 2014): 402-403.
PMID
28036449
Source
epmc
Published In
Medical physics
Volume
41
Issue
6
Publish Date
2014
Start Page
402
End Page
403
DOI
10.1118/1.4889085

Task-based strategy for optimized contrast enhanced breast imaging: Analysis of six imaging techniques for mammography and tomosynthesis

Authors
Ikejimba, LC; Kiarashi, N; Ghate, SV; Samei, E; Lo, JY
MLA Citation
Ikejimba, LC, Kiarashi, N, Ghate, SV, Samei, E, and Lo, JY. "Task-based strategy for optimized contrast enhanced breast imaging: Analysis of six imaging techniques for mammography and tomosynthesis." Medical Physics 41.6 (May 20, 2014): 061908-061908.
Source
crossref
Published In
Medical physics
Volume
41
Issue
6
Publish Date
2014
Start Page
061908
End Page
061908
DOI
10.1118/1.4873317

A fast poly-energetic iterative FBP algorithm.

The beam hardening (BH) effect can influence medical interpretations in two notable ways. First, high attenuation materials, such as bones, can induce strong artifacts, which severely deteriorate the image quality. Second, voxel values can significantly deviate from the real values, which can lead to unreliable quantitative evaluation results. Some iterative methods have been proposed to eliminate the BH effect, but they cannot be widely applied for clinical practice because of the slow computational speed. The purpose of this study was to develop a new fast and practical poly-energetic iterative filtered backward projection algorithm (piFBP). The piFBP is composed of a novel poly-energetic forward projection process and a robust FBP-type backward updating process. In the forward projection process, an adaptive base material decomposition method is presented, based on which diverse body tissues (e.g., lung, fat, breast, soft tissue, and bone) and metal implants can be incorporated to accurately evaluate poly-energetic forward projections. In the backward updating process, one robust and fast FBP-type backward updating equation with a smoothing kernel is introduced to avoid the noise accumulation in the iteration process and to improve the convergence properties. Two phantoms were designed to quantitatively validate our piFBP algorithm in terms of the beam hardening index (BIdx) and the noise index (NIdx). The simulation results showed that piFBP possessed fast convergence speed, as the images could be reconstructed within four iterations. The variation range of the BIdx's of various tissues across phantom size and spectrum were reduced from [-7.5, 17.5] for FBP to [-0.1, 0.1] for piFBP while the NIdx's were maintained in the same low level (about [0.3, 1.7]). When a metal implant presented in a complex phantom, piFBP still had excellent reconstruction performance, as the variation range of the BIdx's of body tissues were reduced from [-2.9, 15.9] for FBP to [-0.3, 0.3] for piFBP and the magnitude of the BIdx of the metal implant was reduced from 23.3 to 1.3. The proposed algorithm piFBP can effectively eliminate beam hardening artifacts caused by bones, greatly reduce metal artifacts caused by metal implants, and quantitatively reconstruct accurate images with poly-energetic spectrum. Its fast reconstruction speed and excellent performance make it ready for clinical applications on the current single spectrum CT scanners.

Authors
Lin, Y; Samei, E
MLA Citation
Lin, Y, and Samei, E. "A fast poly-energetic iterative FBP algorithm." Physics in medicine and biology 59.7 (April 2014): 1655-1678.
PMID
24614805
Source
epmc
Published In
Physics in Medicine and Biology
Volume
59
Issue
7
Publish Date
2014
Start Page
1655
End Page
1678
DOI
10.1088/0031-9155/59/7/1655

A set of 4D pediatric XCAT reference phantoms for multimodality research.

The authors previously developed an adult population of 4D extended cardiac-torso (XCAT) phantoms for multimodality imaging research. In this work, the authors develop a reference set of 4D pediatric XCAT phantoms consisting of male and female anatomies at ages of newborn, 1, 5, 10, and 15 years. These models will serve as the foundation from which the authors will create a vast population of pediatric phantoms for optimizing pediatric CT imaging protocols.Each phantom was based on a unique set of CT data from a normal patient obtained from the Duke University database. The datasets were selected to best match the reference values for height and weight for the different ages and genders according to ICRP Publication 89. The major organs and structures were segmented from the CT data and used to create an initial pediatric model defined using nonuniform rational B-spline surfaces. The CT data covered the entire torso and part of the head. To complete the body, the authors manually added on the top of the head and the arms and legs using scaled versions of the XCAT adult models or additional models created from cadaver data. A multichannel large deformation diffeomorphic metric mapping algorithm was then used to calculate the transform from a template XCAT phantom (male or female 50th percentile adult) to the target pediatric model. The transform was applied to the template XCAT to fill in any unsegmented structures within the target phantom and to implement the 4D cardiac and respiratory models in the new anatomy. The masses of the organs in each phantom were matched to the reference values given in ICRP Publication 89. The new reference models were checked for anatomical accuracy via visual inspection.The authors created a set of ten pediatric reference phantoms that have the same level of detail and functionality as the original XCAT phantom adults. Each consists of thousands of anatomical structures and includes parameterized models for the cardiac and respiratory motions. Based on patient data, the phantoms capture the anatomic variations of childhood, such as the development of bone in the skull, pelvis, and long bones, and the growth of the vertebrae and organs. The phantoms can be combined with existing simulation packages to generate realistic pediatric imaging data from different modalities.The development of patient-derived pediatric computational phantoms is useful in providing variable anatomies for simulation. Future work will expand this ten-phantom base to a host of pediatric phantoms representative of the public at large. This can provide a means to evaluate and improve pediatric imaging devices and to optimize CT protocols in terms of image quality and radiation dose.

Authors
Norris, H; Zhang, Y; Bond, J; Sturgeon, GM; Minhas, A; Tward, DJ; Ratnanather, JT; Miller, MI; Frush, D; Samei, E; Segars, WP
MLA Citation
Norris, H, Zhang, Y, Bond, J, Sturgeon, GM, Minhas, A, Tward, DJ, Ratnanather, JT, Miller, MI, Frush, D, Samei, E, and Segars, WP. "A set of 4D pediatric XCAT reference phantoms for multimodality research." Medical physics 41.3 (March 2014): 033701-.
PMID
24593745
Source
epmc
Published In
Medical physics
Volume
41
Issue
3
Publish Date
2014
Start Page
033701
DOI
10.1118/1.4864238

Comparison of patient specific dose metrics between chest radiography, tomosynthesis, and CT for adult patients of wide ranging body habitus.

Given the radiation concerns inherent to the x-ray modalities, accurately estimating the radiation doses that patients receive during different imaging modalities is crucial. This study estimated organ doses, effective doses, and risk indices for the three clinical chest x-ray imaging techniques (chest radiography, tomosynthesis, and CT) using 59 anatomically variable voxelized phantoms and Monte Carlo simulation methods.A total of 59 computational anthropomorphic male and female extended cardiac-torso (XCAT) adult phantoms were used in this study. Organ doses and effective doses were estimated for a clinical radiography system with the capability of conducting chest radiography and tomosynthesis (Definium 8000, VolumeRAD, GE Healthcare) and a clinical CT system (LightSpeed VCT, GE Healthcare). A Monte Carlo dose simulation program (PENELOPE, version 2006, Universitat de Barcelona, Spain) was used to mimic these two clinical systems. The Duke University (Durham, NC) technique charts were used to determine the clinical techniques for the radiographic modalities. An exponential relationship between CTDIvol and patient diameter was used to determine the absolute dose values for CT. The simulations of the two clinical systems compute organ and tissue doses, which were then used to calculate effective dose and risk index. The calculation of the two dose metrics used the tissue weighting factors from ICRP Publication 103 and BEIR VII report.The average effective dose of the chest posteroanterior examination was found to be 0.04 mSv, which was 1.3% that of the chest CT examination. The average effective dose of the chest tomosynthesis examination was found to be about ten times that of the chest posteroanterior examination and about 12% that of the chest CT examination. With increasing patient average chest diameter, both the effective dose and risk index for CT increased considerably in an exponential fashion, while these two dose metrics only increased slightly for radiographic modalities and for chest tomosynthesis. Effective and organ doses normalized to mAs all illustrated an exponential decrease with increasing patient size. As a surface organ, breast doses had less correlation with body size than that of lungs or liver.Patient body size has a much greater impact on radiation dose of chest CT examinations than chest radiography and tomosynthesis. The size of a patient should be considered when choosing the best thoracic imaging modality.

Authors
Zhang, Y; Li, X; Segars, WP; Samei, E
MLA Citation
Zhang, Y, Li, X, Segars, WP, and Samei, E. "Comparison of patient specific dose metrics between chest radiography, tomosynthesis, and CT for adult patients of wide ranging body habitus." Medical physics 41.2 (February 2014): 023901-.
PMID
24506654
Source
epmc
Published In
Medical physics
Volume
41
Issue
2
Publish Date
2014
Start Page
023901
DOI
10.1118/1.4859315

An efficient polyenergetic SART (pSART) reconstruction algorithm for quantitative myocardial CT perfusion.

In quantitative myocardial CT perfusion imaging, beam hardening effect due to dense bone and high concentration iodinated contrast agent can result in visible artifacts and inaccurate CT numbers. In this paper, an efficient polyenergetic Simultaneous Algebraic Reconstruction Technique (pSART) was presented to eliminate the beam hardening artifacts and to improve the CT quantitative imaging ability.Our algorithm made three a priori assumptions: (1) the human body is composed of several base materials (e.g., fat, breast, soft tissue, bone, and iodine); (2) images can be coarsely segmented to two types of regions, i.e., nonbone regions and noniodine regions; and (3) each voxel can be decomposed into a mixture of two most suitable base materials according to its attenuation value and its corresponding region type information. Based on the above assumptions, energy-independent accumulated effective lengths of all base materials can be fast computed in the forward ray-tracing process and be used repeatedly to obtain accurate polyenergetic projections, with which a SART-based equation can correctly update each voxel in the backward projecting process to iteratively reconstruct artifact-free images. This approach effectively reduces the influence of polyenergetic x-ray sources and it further enables monoenergetic images to be reconstructed at any arbitrarily preselected target energies. A series of simulation tests were performed on a size-variable cylindrical phantom and a realistic anthropomorphic thorax phantom. In addition, a phantom experiment was also performed on a clinical CT scanner to further quantitatively validate the proposed algorithm.The simulations with the cylindrical phantom and the anthropomorphic thorax phantom showed that the proposed algorithm completely eliminated beam hardening artifacts and enabled quantitative imaging across different materials, phantom sizes, and spectra, as the absolute relative errors were reduced from [-7.5%, 12.1%] for SART to [-0.1%, 0.1%] for pSART. When using low kVp spectra and high reference energies, pSART also showed improved reconstruction efficiency in terms of convergence speed compared to the conventional SART algorithm. The phantom experiment on a clinical CT scanner indicated that the quantitative advantage of pSART is realizable in experimental CT acquisition, as the absolute relative errors across material inserts were less than 0.4%.By incorporatinga priori information (material attenuation coefficients, x-ray source spectrum, and region type information) into the reconstruction process, the proposed pSART algorithm could effectively eliminate beam hardening artifacts, reconstruct the accurate attenuation coefficients for precise quantitative imaging, and accelerate the reconstruction process.

Authors
Lin, Y; Samei, E
MLA Citation
Lin, Y, and Samei, E. "An efficient polyenergetic SART (pSART) reconstruction algorithm for quantitative myocardial CT perfusion." Medical physics 41.2 (February 2014): 021911-.
PMID
24506632
Source
epmc
Published In
Medical physics
Volume
41
Issue
2
Publish Date
2014
Start Page
021911
DOI
10.1118/1.4863481

Pediatric chest and abdominopelvic CT: organ dose estimation based on 42 patient models.

PURPOSE: To estimate organ dose from pediatric chest and abdominopelvic computed tomography (CT) examinations and evaluate the dependency of organ dose coefficients on patient size and CT scanner models. MATERIALS AND METHODS: The institutional review board approved this HIPAA-compliant study and did not require informed patient consent. A validated Monte Carlo program was used to perform simulations in 42 pediatric patient models (age range, 0-16 years; weight range, 2-80 kg; 24 boys, 18 girls). Multidetector CT scanners were modeled on those from two commercial manufacturers (LightSpeed VCT, GE Healthcare, Waukesha, Wis; SOMATOM Definition Flash, Siemens Healthcare, Forchheim, Germany). Organ doses were estimated for each patient model for routine chest and abdominopelvic examinations and were normalized by volume CT dose index (CTDI(vol)). The relationships between CTDI(vol)-normalized organ dose coefficients and average patient diameters were evaluated across scanner models. RESULTS: For organs within the image coverage, CTDI(vol)-normalized organ dose coefficients largely showed a strong exponential relationship with the average patient diameter (R(2) > 0.9). The average percentage differences between the two scanner models were generally within 10%. For distributed organs and organs on the periphery of or outside the image coverage, the differences were generally larger (average, 3%-32%) mainly because of the effect of overranging. CONCLUSION: It is feasible to estimate patient-specific organ dose for a given examination with the knowledge of patient size and the CTDI(vol). These CTDI(vol)-normalized organ dose coefficients enable one to readily estimate patient-specific organ dose for pediatric patients in clinical settings. This dose information, and, as appropriate, attendant risk estimations, can provide more substantive information for the individual patient for both clinical and research applications and can yield more expansive information on dose profiles across patient populations within a practice.

Authors
Tian, X; Li, X; Segars, WP; Paulson, EK; Frush, DP; Samei, E
MLA Citation
Tian, X, Li, X, Segars, WP, Paulson, EK, Frush, DP, and Samei, E. "Pediatric chest and abdominopelvic CT: organ dose estimation based on 42 patient models." Radiology 270.2 (February 2014): 535-547.
PMID
24126364
Source
pubmed
Published In
Radiology
Volume
270
Issue
2
Publish Date
2014
Start Page
535
End Page
547
DOI
10.1148/radiol.13122617

Population of 100 realistic, patient-based computerized breast phantoms for multi-modality imaging research

Breast imaging is an important area of research with many new Techniques being investigated To further reduce The morbidity and mortality of breast cancer Through early detection. Computerized phantoms can provide an essential Tool To quantitatively compare new imaging systems and Techniques. Current phantoms, however, lack sufficient realism in depicting The complex 3D anatomy of The breast. In This work, we created one-hundred realistic and detailed 3D computational breast phantoms based on high-resolution CT datasets from normal patients. We also developed a finiteelement application To simulate different compression states of The breast, making The phantoms applicable To multimodality imaging research. The breast phantoms and Tools developed in This work were packaged into user-friendly software applications To distribute for breast imaging research. © 2014 SPIE.

Authors
Segars, WP; Veress, AI; Wells, JR; Sturgeon, GM; Kiarashi, N; Lo, JY; Samei, E; Dobbins, JT
MLA Citation
Segars, WP, Veress, AI, Wells, JR, Sturgeon, GM, Kiarashi, N, Lo, JY, Samei, E, and Dobbins, JT. "Population of 100 realistic, patient-based computerized breast phantoms for multi-modality imaging research." January 1, 2014.
Source
scopus
Published In
Proceedings of SPIE
Volume
9033
Publish Date
2014
DOI
10.1117/12.2043868

X-ray coherent scatter imaging for surgical margin detection: A Monte Carlo study

Instead of having the entire breast removed (a mastectomy), breast cancer patients often receive a breast con-serving surgery (BCS) for removal of only the breast tumor. If post-surgery analysis reveals ta missed margin around the tumor tissue excised through the BCS procedure, the physician must often call the patient back for another surgery, which is both difficult and risky for the patient. If this “margin detectionâ€could be performed during the BCS procedure itself, the surgical team could use the analysis to ensure that all tumor tissue was removed in a single surgery, thereby potentially reducing the number of call backs from breast cancer surgery. We describe here a potential technique to detect surgical tumor margins in breast cancer using x-ray coherent scatter imaging. In this study, we demonstrate the imaging ability of this technique using Monte Carlo simulations. © 2014 SPIE.

Authors
Lakshmanan, MN; Kapadia, AJ; Harrawood, BP; Brady, D; Samei, E
MLA Citation
Lakshmanan, MN, Kapadia, AJ, Harrawood, BP, Brady, D, and Samei, E. "X-ray coherent scatter imaging for surgical margin detection: A Monte Carlo study." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 9033 (January 1, 2014).
Source
scopus
Published In
Proceedings of SPIE
Volume
9033
Publish Date
2014
DOI
10.1117/12.2043856

A second generation of physical anthropomorphic 3D breast phantoms based on human subject data

Previous fabrication of anthropomorphic breast phantoms has demonstrated Their viability as a model for 2D (mammography) and 3D (tomosynthesis) breast imaging systems. Further development of These models will be essential for The evaluation of breast x-ray systems. There is also The potential To use Them as The ground Truth in virtual clinical Trials. The first generation of phantoms was segmented from human subject dedicated breast computed Tomography data and fabricated into physical models using highresolution 3D printing. Two variations were made. The first was a multi-material model (doublet) printed with Two photopolymers To represent glandular and adipose Tissues with The greatest physical contrast available, mimicking 75% and 35% glandular Tissue. The second model was printed with a single 75% glandular equivalent photopolymer (singlet) To represent glandular Tissue, which can be filled independently with an adipose-equivalent material such as oil. For This study, we have focused on improving The latter, The singlet phantom. First, The Temporary oil filler has been replaced with a permanent adipose-equivalent urethane-based polymer. This offers more realistic contrast as compared To The multi-material approach at The expense of air bubbles and pockets That form during The filling process. Second, microcalcification clusters have been included in The singlet model via crushed eggshells, which have very similar chemical composition To calcifications in vivo. The results from These new prototypes demonstrate significant improvement over The first generation of anthropomorphic physical phantoms. © 2014 SPIE.

Authors
Nolte, A; Kiarashi, N; Samei, E; Segars, WP; Lo, JY
MLA Citation
Nolte, A, Kiarashi, N, Samei, E, Segars, WP, and Lo, JY. "A second generation of physical anthropomorphic 3D breast phantoms based on human subject data." January 1, 2014.
Source
scopus
Published In
Proceedings of SPIE
Volume
9033
Publish Date
2014
DOI
10.1117/12.2043703

A task-based comparison of two reconstruction algorithms for digital breast tomosynthesis

Digital breast tomosynthesis (DBT) generates 3-D reconstructions of the breast by taking X-Ray projections at various angles around the breast. DBT improves cancer detection as it minimizes tissue overlap that is present in traditional 2-D mammography. In this work, two methods of reconstruction, filtered backprojection (FBP) and the Newton-Raphson iterative reconstruction were used to create 3-D reconstructions from phantom images acquired on a breast tomosynthesis system. The task based image analysis method was used to compare the performance of each reconstruction technique. The task simulated a 10mm lesion within the breast containing iodine concentrations between 0.0mg/ml and 8.6mg/ml. The TTF was calculated using the reconstruction of an edge phantom, and the NPS was measured with a structured breast phantom (CIRS 020) over different exposure levels. The detectability index d’was calculated to assess image quality of the reconstructed phantom images. Image quality was assessed for both conventional, single energy and dual energy subtracted reconstructions. Dose allocation between the high and low energy scans was also examined. Over the full range of dose allocations, the iterative reconstruction yielded a higher detectability index than the FBP for single energy reconstructions. For dual energy subtraction, detectability index was maximized when most of the dose was allocated to the high energy image. With that dose allocation, the performance trend for reconstruction algorithms reversed; FBP performed better than the corresponding iterative reconstruction. However, FBP performance varied very erratically with changing dose allocation. Therefore, iterative reconstruction is preferred for both imaging modalities despite underperforming dual energy FBP, as it provides stable results. © 2014 SPIE.

Authors
Mahadevan, R; Ikejimba, LC; Lin, Y; Samei, E; Lo, JY
MLA Citation
Mahadevan, R, Ikejimba, LC, Lin, Y, Samei, E, and Lo, JY. "A task-based comparison of two reconstruction algorithms for digital breast tomosynthesis." January 1, 2014.
Source
scopus
Published In
Proceedings of SPIE
Volume
9033
Publish Date
2014
DOI
10.1117/12.2043829

Validation of an image-based technique to assess the perceptual quality of clinical chest radiographs with an observer study

We previously proposed a novel image-based quality assessment technique1 to assess the perceptual quality of clinical chest radiographs. In this paper, an observer study was designed and conducted to systematically validate this technique. Ten metrics were involved in the observer study, i.e., lung grey level, lung detail, lung noise, riblung contrast, rib sharpness, mediastinum detail, mediastinum noise, mediastinum alignment, subdiaphragm-lung contrast, and subdiaphragm area. For each metric, three tasks were successively presented to the observers. In each task, six ROI images were randomly presented in a row and observers were asked to rank the images only based on a designated quality and disregard the other qualities. A range slider on the top of the images was used for observers to indicate the acceptable range based on the corresponding perceptual attribute. Five boardcertificated radiologists from Duke participated in this observer study on a DICOM calibrated diagnostic display workstation and under low ambient lighting conditions. The observer data were analyzed in terms of the correlations between the observer ranking orders and the algorithmic ranking orders. Based on the collected acceptable ranges, quality consistency ranges were statistically derived. The observer study showed that, for each metric, the averaged ranking orders of the participated observers were strongly correlated with the algorithmic orders. For the lung grey level, the observer ranking orders completely accorded with the algorithmic ranking orders. The quality consistency ranges derived from this observer study were close to these derived from our previous study. The observer study indicates that the proposed image-based quality assessment technique provides a robust reflection of the perceptual image quality of the clinical chest radiographs. The derived quality consistency ranges can be used to automatically predict the acceptability of a clinical chest radiograph. © 2014 SPIE.

Authors
Lin, Y; Choudhury, KR; McAdams, HP; Foos, DH; Samei, E
MLA Citation
Lin, Y, Choudhury, KR, McAdams, HP, Foos, DH, and Samei, E. "Validation of an image-based technique to assess the perceptual quality of clinical chest radiographs with an observer study." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 9033 (January 1, 2014).
Source
scopus
Published In
Proceedings of SPIE
Volume
9033
Publish Date
2014
DOI
10.1117/12.2043993

Design of anthropomorphic Textured phantoms for CT performance evaluation

Commercially available computed Tomography (CT) Technologies such as iterative reconstruction (IR) have The potential To enable reduced patient doses while maintaining diagnostic image quality. However, systematically determining safe dose reduction levels for IR algorithms is a challenging Task due To Their nonlinear nature. Most attempts To evaluate IR algorithms rely on measurements made in uniform phantoms. Such measurements may overstate The dose reduction potential of IR because They don’t account for The complex relationship between anatomical variability and image quality. The purpose of This study was To design anatomically informed Textured phantoms for CT performance evaluation. Two phantoms were designed To represent lung and soft-tissue Textures. The lung phantom includes intricate vessel-like structures along with embedded nodules (spherical, lobulated, and spiculated). The soft Tissue phantom was designed based on a Three-dimensional clustered lumpy background with included low-contrast lesions (spherical and anthropomorphic). The phantoms were built using rapid prototyping (3D printing) Technology and imaged on a modern multi-slice clinical CT scanner To assess The noise performance of a commercial IR algorithm in The context of uniform and Textured backgrounds. Fifty repeated acquisitions were acquired for each background Type and noise was assessed by measuring pixel standard deviation, across The ensemble of repeated acquisitions. For pixels in uniform areas, The IR algorithm reduced noise magnitude (STD) by 60% (compared To FBP). However, for edge pixels, The noise magnitude in The IR images ranged from 20% higher To 40% lower compared To FBP. In all FBP images and in IR images of The uniform phantom, noise appeared To be globally non-stationary (i.e., spatially dependent) but locally stationary (within a reasonably small region of interest). In The IR images of The Textured phantoms, The noise was globally and locally non-stationary. © 2014 SPIE.

Authors
Solomon, J; Bochud, F; Samei, E
MLA Citation
Solomon, J, Bochud, F, and Samei, E. "Design of anthropomorphic Textured phantoms for CT performance evaluation." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 9033 (January 1, 2014).
Source
scopus
Published In
Proceedings of SPIE
Volume
9033
Publish Date
2014
DOI
10.1117/12.2043555

The development of a population of 4D pediatric XCAT phantoms for CT imaging research and optimization

With The increased use of CT examinations, The associated radiation dose has become a large concern, especially for pediatrics. Much research has focused on reducing radiation dose Through new scanning and reconstruction methods. Computational phantoms provide an effective and efficient means for evaluating image quality, patient-specific dose, and organ-specific dose in CT. We previously developed a set of highly-detailed 4D reference pediatric XCAT phantoms at ages of newborn, 1, 5, 10, and 15 years with organ and Tissues masses matched To ICRP Publication 89 values. We now extend This reference set To a series of 64 pediatric phantoms of a variety of ages and height and weight percentiles, representative of The public at large. High resolution PET-CT data was reviewed by a practicing experienced radiologist for anatomic regularity and was Then segmented with manual and semi-Automatic methods To form a Target model. A Multi-Channel Large Deformation Diffeomorphic Metric Mapping (MC-LDDMM) algorithm was used To calculate The Transform from The best age matching pediatric reference phantom To The patient Target. The Transform was used To complete The Target, filling in The non-segmented structures and defining models for The cardiac and respiratory motions. The complete phantoms, consisting of Thousands of structures, were Then manually inspected for anatomical accuracy. 3D CT data was simulated from The phantoms To demonstrate Their ability To generate realistic, patient quality imaging data. The population of pediatric phantoms developed in This work provides a vital Tool To investigate dose reduction Techniques in 3D and 4D pediatric CT. © 2014 SPIE.

Authors
Norris, H; Zhang, Y; Frush, J; Sturgeon, GM; Minhas, A; Tward, DJ; Ratnanather, JT; Miller, MI; Frush, D; Samei, E; Segars, WP
MLA Citation
Norris, H, Zhang, Y, Frush, J, Sturgeon, GM, Minhas, A, Tward, DJ, Ratnanather, JT, Miller, MI, Frush, D, Samei, E, and Segars, WP. "The development of a population of 4D pediatric XCAT phantoms for CT imaging research and optimization." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 9033 (January 1, 2014).
Source
scopus
Published In
Proceedings of SPIE
Volume
9033
Publish Date
2014
DOI
10.1117/12.2043777

Prospective optimization of CT under Tube current modulation: I. organ dose

In an environment in which computed Tomography (CT) has become an indispensable diagnostic Tool employed with great frequency, dose concerns at The population level have become a subject of public attention. In That regard, optimizing radiation dose has become a core problem To The CT community. As a fundamental step To optimize radiation dose, it is crucial To effectively quantify radiation dose for a given CT exam. Such dose estimates need To be patient-specific To reflect individual radiation burden. It further needs To be prospective so That The scanning parameters can be dynamically adjusted before The scan is performed. The purpose of This study was To prospectively estimate organ dose in abdominopelvic CT exams under Tube current modulation (TCM). CTDIvol-normalized-organ dose coefficients (hfixed) for fixed Tube current were first estimated using a validated Monte Carlo simulation program and 58 computational phantoms. To account for The effect of TCM scheme, a weighted CTDIvol was computed for each organ based on The Tube current modulation profile. The organ dose was predicted by multiplying The weighted CTDIvol with The organ dose coefficients (h fixed). To quantify prediction accuracy, each predicted organ dose was compared with organ dose simulated from Monte Carlo program with TCM profile explicitly modeled. The predicted organ dose showed good agreement with simulated organ dose across all organs and modulation strengths. For an average CTDIvol of a CT exam of 10 mGy, The absolute median error across all organs were 0.64 mGy (-0.21 and 0.97 for 25th and 75th percentiles, respectively). The percentage differences (normalized by CTDIvol of The exam) were within 15%. This study developed a quantitative model To predict organ dose under clinical abdominopelvic scans. Such information may aid in The optimization of CT protocols. © 2014 SPIE.

Authors
Tian, X; Li, X; Segars, WP; Frush, D; Samei, E
MLA Citation
Tian, X, Li, X, Segars, WP, Frush, D, and Samei, E. "Prospective optimization of CT under Tube current modulation: I. organ dose." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 9033 (January 1, 2014).
Source
scopus
Published In
Proceedings of SPIE
Volume
9033
Publish Date
2014
DOI
10.1117/12.2043858

Prospective optimization of CT under tube current modulation: II. image quality

Despite the significant clinical benefits of computed tomography (CT) in providing diagnostic information for a broad range of diseases, concerns have been raised regarding the potential cancer risk induced by CT radiation exposure. In that regard, optimizing CT protocols and minimizing radiation dose have become the core problem for the CT community. To develop strategies to optimize radiation dose, it is crucial to effectively characterize CT image quality. Such image quality estimates need to be prospective to ensure that optimization can be performed before the scan is initiated. The purpose of this study was to establish a phantombased methodology to predict quantum noise in CT images as a first step in our image quality prediction. Quantum noise was measured using a variable-sized phantom under clinical protocols. The mathematical relationship between noise and water-equivalent-diameter (Dw) was further established. The prediction was achieved by ascribing a noise value to a patient according to the patient’s water-equivalent- diameter. The prediction accuracy was evaluated in anthropomorphic phantoms across a broad range of sizes, anatomy, and reconstruction algorithms. The differences between the measured and predicted noise were within 10% for anthropomorphic phantoms across all sizes and anatomy. This study proposed a practically applicable technique to predict noise in CT images. With a prospective estimation of image quality level, the scanning parameters can then by adjusted to ensure optimized imaging performance. © 2014 SPIE.

Authors
Tian, X; Wilson, J; Frush, D; Samei, E
MLA Citation
Tian, X, Wilson, J, Frush, D, and Samei, E. "Prospective optimization of CT under tube current modulation: II. image quality." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 9033 (January 1, 2014).
Source
scopus
Published In
Proceedings of SPIE
Volume
9033
Publish Date
2014
DOI
10.1117/12.2044013

A refined methodology for modeling volume quantification performance in CT

The utility of CT lung nodule volume quantification technique depends on the precision of the quantification. To enable the evaluation of quantification precision, we previously developed a mathematical model that related precision to image resolution and noise properties in uniform backgrounds in terms of an estimability index (e’). The e’was shown to predict empirical precision across 54 imaging and reconstruction protocols, but with different correlation qualities for FBP and iterative reconstruction (IR) due to the non-linearity of IR impacted by anatomical structure. To better account for the non-linearity of IR, this study aimed to refine the noise characterization of the model in the presence of textured backgrounds. Repeated scans of an anthropomorphic lung phantom were acquired. Subtracted images were used to measure the image quantum noise, which was then used to adjust the noise component of the e’calculation measured from a uniform region. In addition to the model refinement, the validation of the model was further extended to 2 nodule sizes (5 and 10 mm) and 2 segmentation algorithms. Results showed that the magnitude of IR’s quantum noise was significantly higher in structured backgrounds than in uniform backgrounds (ASiR, 30-50%; MBIR, 100-200%). With the refined model, the correlation between e’values and empirical precision no longer depended on reconstruction algorithm. In conclusion, the model with refined noise characterization relfected the nonlinearity of iterative reconstruction in structured background, and further showed successful prediction of quantification precision across a variety of nodule sizes, dose levels, slice thickness, reconstruction algorithms, and segmentation software. © 2014 SPIE.

Authors
Chen, B; Wilson, J; Samei, E
MLA Citation
Chen, B, Wilson, J, and Samei, E. "A refined methodology for modeling volume quantification performance in CT." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 9033 (January 1, 2014).
Source
scopus
Published In
Proceedings of SPIE
Volume
9033
Publish Date
2014
DOI
10.1117/12.2044004

Improved nuclear medicine uniformity assessment with noise texture analysis.

UNLABELLED: Because γ cameras are generally susceptible to environmental conditions and system vulnerabilities, they require routine evaluation of uniformity performance. The metrics for such evaluations are commonly pixel value-based. Although these metrics are typically successful at identifying regional nonuniformities, they often do not adequately reflect subtle periodic structures; therefore, additional visual inspections are required. The goal of this project was to develop, test, and validate a new uniformity analysis metric capable of accurately identifying structures and patterns present in nuclear medicine flood-field uniformity images. METHODS: A new uniformity assessment metric, termed the structured noise index (SNI), was based on the 2-dimensional noise power spectrum (NPS). The contribution of quantum noise was subtracted from the NPS of a flood-field uniformity image, resulting in an NPS representing image artifacts. A visual response filter function was then applied to both the original NPS and the artifact NPS. A single quantitative score was calculated on the basis of the magnitude of the artifact. To verify the validity of the SNI, an observer study was performed with 5 expert nuclear medicine physicists. The correlation between the SNI and the visual score was assessed with Spearman rank correlation analysis. The SNI was also compared with pixel value-based assessment metrics modeled on the National Electrical Manufacturers Association standard for integral uniformity in both the useful field of view (UFOV) and the central field of view (CFOV). RESULTS: The SNI outperformed the pixel value-based metrics in terms of its correlation with the visual score (ρ values for the SNI, integral UFOV, and integral CFOV were 0.86, 0.59, and 0.58, respectively). The SNI had 100% sensitivity for identifying both structured and nonstructured nonuniformities; for the integral UFOV and CFOV metrics, the sensitivities were only 62% and 54%, respectively. The overall positive predictive value of the SNI was 87%; for the integral UFOV and CFOV metrics, the positive predictive values were only 67% and 50%, respectively. CONCLUSION: The SNI accurately identified both structured and nonstructured flood-field nonuniformities and correlated closely with expert visual assessment. Compared with traditional pixel value-based analysis, the SNI showed superior performance in terms of its correlation with visual perception. The SNI method is effective for detecting and quantifying visually apparent nonuniformities and may reduce the need for more subjective visual analyses.

Authors
Nelson, JS; Christianson, OI; Harkness, BA; Madsen, MT; Mah, E; Thomas, SR; Zaidi, H; Samei, E
MLA Citation
Nelson, JS, Christianson, OI, Harkness, BA, Madsen, MT, Mah, E, Thomas, SR, Zaidi, H, and Samei, E. "Improved nuclear medicine uniformity assessment with noise texture analysis." J Nucl Med 55.1 (January 2014): 169-174.
PMID
24212975
Source
pubmed
Published In
Journal of nuclear medicine : official publication, Society of Nuclear Medicine
Volume
55
Issue
1
Publish Date
2014
Start Page
169
End Page
174
DOI
10.2967/jnumed.113.125450

Dose index analytics: More than a low number

Authors
Samei, E; Christianson, O
MLA Citation
Samei, E, and Christianson, O. "Dose index analytics: More than a low number." Journal of the American College of Radiology 11.8 (2014): 832-834.
Source
scopus
Published In
Journal of the American College of Radiology
Volume
11
Issue
8
Publish Date
2014
Start Page
832
End Page
834
DOI
10.1016/j.jacr.2014.05.004

Dose index analytics: More than a low number

Authors
Samei, E; Christianson, O
MLA Citation
Samei, E, and Christianson, O. "Dose index analytics: More than a low number." Journal of the American College of Radiology 11.8 (2014): 832-834.
Source
scopus
Published In
Journal of the American College of Radiology
Volume
11
Issue
8
Publish Date
2014
Start Page
832
End Page
834
DOI
10.1016/j.jacr.2014.05.004

Dose coefficients in pediatric and adult abdominopelvic CT based on 100 patient models.

Recent studies have shown the feasibility of estimating patient dose from a CT exam using CTDI(vol)-normalized-organ dose (denoted as h), DLP-normalized-effective dose (denoted as k), and DLP-normalized-risk index (denoted as q). However, previous studies were limited to a small number of phantom models. The purpose of this work was to provide dose coefficients (h, k, and q) across a large number of computational models covering a broad range of patient anatomy, age, size percentile, and gender. The study consisted of 100 patient computer models (age range, 0 to 78 y.o.; weight range, 2-180 kg) including 42 pediatric models (age range, 0 to 16 y.o.; weight range, 2-80 kg) and 58 adult models (age range, 18 to 78 y.o.; weight range, 57-180 kg). Multi-detector array CT scanners from two commercial manufacturers (LightSpeed VCT, GE Healthcare; SOMATOM Definition Flash, Siemens Healthcare) were included. A previously-validated Monte Carlo program was used to simulate organ dose for each patient model and each scanner, from which h, k, and q were derived. The relationships between h, k, and q and patient characteristics (size, age, and gender) were ascertained. The differences in conversion coefficients across the scanners were further characterized. CTDI(vol)-normalized-organ dose (h) showed an exponential decrease with increasing patient size. For organs within the image coverage, the average differences of h across scanners were less than 15%. That value increased to 29% for organs on the periphery or outside the image coverage, and to 8% for distributed organs, respectively. The DLP-normalized-effective dose (k) decreased exponentially with increasing patient size. For a given gender, the DLP-normalized-risk index (q) showed an exponential decrease with both increasing patient size and patient age. The average differences in k and q across scanners were 8% and 10%, respectively. This study demonstrated that the knowledge of patient information and CTDIvol/DLP values may be used to estimate organ dose, effective dose, and risk index in abdominopelvic CT based on the coefficients derived from a large population of pediatric and adult patients.

Authors
Tian, X; Li, X; Segars, WP; Frush, DP; Paulson, EK; Samei, E
MLA Citation
Tian, X, Li, X, Segars, WP, Frush, DP, Paulson, EK, and Samei, E. "Dose coefficients in pediatric and adult abdominopelvic CT based on 100 patient models." Phys Med Biol 58.24 (December 21, 2013): 8755-8768.
PMID
24301136
Source
pubmed
Published In
Physics in Medicine and Biology
Volume
58
Issue
24
Publish Date
2013
Start Page
8755
End Page
8768
DOI
10.1088/0031-9155/58/24/8755

Clinical impact of an adaptive statistical iterative reconstruction algorithm for detection of hypervascular liver tumours using a low tube voltage, high tube current MDCT technique

Objectives: To investigate the impact of an adaptive statistical iterative reconstruction (ASiR) algorithm on diagnostic accuracy and confidence for the diagnosis of hypervascular liver tumours, as well as the reader's perception of image quality, using a low tube voltage (80 kVp), high tube current computed tomography (CT) technique. Methods: Forty patients (29 men, 11 women) with 65 hypervascular liver tumours underwent dual energy CT. The 80 kV set of the dual energy acquisition was reconstructed with standard filtered backprojection (FBP) and ASiR at different blending levels. Lesion contrast-to-noise ratio (CNR), reader's confidence for lesion detection and characterisation, and reader's evaluation of image quality were recorded. Results: ASiR yielded significantly higher CNR values compared with FBP (P < 0.0001 for all comparisons). Reader's perception of lesion conspicuity and confidence in the diagnosis of malignancy were also higher with 60 % and 80 % ASiR, compared with FBP (P = 0.01 and < 0.001, respectively). Compared with FBP, ASiR yielded nearly significantly lower specificity for lesion detection and a substantial decrease in the reader's perception of image quality. Conclusions: Compared with the standard FBP algorithm, ASiR significantly improves conspicuity of hypervascular liver lesions. This improvement may come at the cost of decreased specificity and reader's perception of image quality. Key Points: • Adaptive statistical iterative reconstruction algorithms (ASiRs) offer increasing potential in multidetector CT. • An ASiR algorithm significantly improves conspicuity of hypervascular liver lesions at MDCT. • Improved lesion conspicuity translates into increased reader's confidence for diagnosis of malignancy. • False positive findings may increase with ASiR, leading to potentially lower specificity. © 2013 European Society of Radiology.

Authors
Marin, D; Choudhury, KR; Gupta, RT; Ho, LM; Allen, BC; Schindera, ST; Colsher, JG; Samei, E; Nelson, RC
MLA Citation
Marin, D, Choudhury, KR, Gupta, RT, Ho, LM, Allen, BC, Schindera, ST, Colsher, JG, Samei, E, and Nelson, RC. "Clinical impact of an adaptive statistical iterative reconstruction algorithm for detection of hypervascular liver tumours using a low tube voltage, high tube current MDCT technique." European Radiology 23.12 (December 1, 2013): 3325-3335.
Source
scopus
Published In
European Radiology
Volume
23
Issue
12
Publish Date
2013
Start Page
3325
End Page
3335
DOI
10.1007/s00330-013-2964-1

Clinical impact of an adaptive statistical iterative reconstruction algorithm for detection of hypervascular liver tumours using a low tube voltage, high tube current MDCT technique.

OBJECTIVES: To investigate the impact of an adaptive statistical iterative reconstruction (ASiR) algorithm on diagnostic accuracy and confidence for the diagnosis of hypervascular liver tumours, as well as the reader's perception of image quality, using a low tube voltage (80 kVp), high tube current computed tomography (CT) technique. METHODS: Forty patients (29 men, 11 women) with 65 hypervascular liver tumours underwent dual energy CT. The 80 kV set of the dual energy acquisition was reconstructed with standard filtered backprojection (FBP) and ASiR at different blending levels. Lesion contrast-to-noise ratio (CNR), reader's confidence for lesion detection and characterisation, and reader's evaluation of image quality were recorded. RESULTS: ASiR yielded significantly higher CNR values compared with FBP (P < 0.0001 for all comparisons). Reader's perception of lesion conspicuity and confidence in the diagnosis of malignancy were also higher with 60 % and 80 % ASiR, compared with FBP (P = 0.01 and < 0.001, respectively). Compared with FBP, ASiR yielded nearly significantly lower specificity for lesion detection and a substantial decrease in the reader's perception of image quality. CONCLUSIONS: Compared with the standard FBP algorithm, ASiR significantly improves conspicuity of hypervascular liver lesions. This improvement may come at the cost of decreased specificity and reader's perception of image quality.

Authors
Marin, D; Choudhury, KR; Gupta, RT; Ho, LM; Allen, BC; Schindera, ST; Colsher, JG; Samei, E; Nelson, RC
MLA Citation
Marin, D, Choudhury, KR, Gupta, RT, Ho, LM, Allen, BC, Schindera, ST, Colsher, JG, Samei, E, and Nelson, RC. "Clinical impact of an adaptive statistical iterative reconstruction algorithm for detection of hypervascular liver tumours using a low tube voltage, high tube current MDCT technique." Eur Radiol 23.12 (December 2013): 3325-3335.
PMID
23832320
Source
pubmed
Published In
European Radiology
Volume
23
Issue
12
Publish Date
2013
Start Page
3325
End Page
3335
DOI
10.1007/s00330-013-2964-1

Volumetric quantification of lung nodules in CT with iterative reconstruction (ASiR and MBIR).

Volume quantifications of lung nodules with multidetector computed tomography (CT) images provide useful information for monitoring nodule developments. The accuracy and precision of the volume quantification, however, can be impacted by imaging and reconstruction parameters. This study aimed to investigate the impact of iterative reconstruction algorithms on the accuracy and precision of volume quantification with dose and slice thickness as additional variables.Repeated CT images were acquired from an anthropomorphic chest phantom with synthetic nodules (9.5 and 4.8 mm) at six dose levels, and reconstructed with three reconstruction algorithms [filtered backprojection (FBP), adaptive statistical iterative reconstruction (ASiR), and model based iterative reconstruction (MBIR)] into three slice thicknesses. The nodule volumes were measured with two clinical software (A: Lung VCAR, B: iNtuition), and analyzed for accuracy and precision.Precision was found to be generally comparable between FBP and iterative reconstruction with no statistically significant difference noted for different dose levels, slice thickness, and segmentation software. Accuracy was found to be more variable. For large nodules, the accuracy was significantly different between ASiR and FBP for all slice thicknesses with both software, and significantly different between MBIR and FBP for 0.625 mm slice thickness with Software A and for all slice thicknesses with Software B. For small nodules, the accuracy was more similar between FBP and iterative reconstruction, with the exception of ASIR vs FBP at 1.25 mm with Software A and MBIR vs FBP at 0.625 mm with Software A.The systematic difference between the accuracy of FBP and iterative reconstructions highlights the importance of extending current segmentation software to accommodate the image characteristics of iterative reconstructions. In addition, a calibration process may help reduce the dependency of accuracy on reconstruction algorithms, such that volumes quantified from scans of different reconstruction algorithms can be compared. The little difference found between the precision of FBP and iterative reconstructions could be a result of both iterative reconstruction's diminished noise reduction at the edge of the nodules as well as the loss of resolution at high noise levels with iterative reconstruction. The findings do not rule out potential advantage of IR that might be evident in a study that uses a larger number of nodules or repeated scans.

Authors
Chen, B; Barnhart, H; Richard, S; Robins, M; Colsher, J; Samei, E
MLA Citation
Chen, B, Barnhart, H, Richard, S, Robins, M, Colsher, J, and Samei, E. "Volumetric quantification of lung nodules in CT with iterative reconstruction (ASiR and MBIR)." Medical physics 40.11 (November 2013): 111902-.
PMID
24320435
Source
epmc
Published In
Medical physics
Volume
40
Issue
11
Publish Date
2013
Start Page
111902
DOI
10.1118/1.4823463

Estimation of radiation exposure for brain perfusion CT: standard protocol compared with deviations in protocol.

OBJECTIVE: The purpose of this study was to measure the organ doses and estimate the effective dose for the standard brain perfusion CT protocol and erroneous protocols. MATERIALS AND METHODS: An anthropomorphic phantom with metal oxide semiconductor field effect transistor (MOSFET) detectors was scanned on a 64-MDCT scanner. Protocol 1 used a standard brain perfusion protocol with 80 kVp and fixed tube current of 200 mA. Protocol 2 used 120 kVp and fixed tube current of 200 mA. Protocol 3 used 120 kVp with automatic tube current modulation (noise index, 2.4; minimum, 100 mA; maximum, 520 mA). RESULTS: Compared with protocol 1, the effective dose was 2.8 times higher with protocol 2 and 7.8 times higher with protocol 3. For all protocols, the peak dose was highest in the skin, followed by the brain and calvarial marrow. Compared with protocol 1, the peak skin dose was 2.6 times higher with protocol 2 and 6.7 times higher with protocol 3. The peak skin dose for protocol 3 exceeded 3 Gy. The ocular lens received significant scatter radiation: 177 mGy for protocol 2 and 435 mGy for protocol 3, which were 4.6 and 11.3 times the dose for protocol 1, respectively. CONCLUSION: Compared with the standard protocol, erroneous protocols of increasing the tube potential from 80 kVp to 120 kVp will lead to a three- to fivefold increase in organ doses, and concurrent use of high peak kilovoltage with incorrectly programmed tube current modulation can increase dose to organs by 7- to 11-fold. Tube current modulation with a low noise index can lead to doses to the skin and ocular lens that are close to thresholds for tissue reactions.

Authors
Hoang, JK; Wang, C; Frush, DP; Enterline, DS; Samei, E; Toncheva, G; Lowry, C; Yoshizumi, TT
MLA Citation
Hoang, JK, Wang, C, Frush, DP, Enterline, DS, Samei, E, Toncheva, G, Lowry, C, and Yoshizumi, TT. "Estimation of radiation exposure for brain perfusion CT: standard protocol compared with deviations in protocol." AJR Am J Roentgenol 201.5 (November 2013): W730-W734.
PMID
24063388
Source
pubmed
Published In
AJR. American journal of roentgenology
Volume
201
Issue
5
Publish Date
2013
Start Page
W730
End Page
W734
DOI
10.2214/AJR.12.10031

Digital breast tomosynthesis: A concise overview

The proven limited sensitivity of mammography, due to tissue superposition in a 2D image, has motivated the development of alternative 3D imaging systems with minimal ionizing exposure and relatively low cost. The advent of digital detectors facilitated the realization of digital breast tomosynthesis systems, which acquire low-dose projection images of the breast from multiple directions to synthesize slices through the volume of the breast parallel to the plane of the projection images. Although still in its clinical infancy, this imaging system has been studied in a multitude of domains. This concise overview introduces digital breast tomosynthesis and elaborates on the state-of-the-art in its applications and performance. © 2013 Future Medicine Ltd.

Authors
Kiarashi, N; Samei, E
MLA Citation
Kiarashi, N, and Samei, E. "Digital breast tomosynthesis: A concise overview." Imaging in Medicine 5.5 (October 1, 2013): 467-476. (Review)
Source
scopus
Published In
Imaging in Medicine
Volume
5
Issue
5
Publish Date
2013
Start Page
467
End Page
476
DOI
10.2217/iim.13.52

Comparison of conventional and simulated reduced-tube current MDCT for evaluation of suspected appendicitis in the pediatric population.

OBJECTIVE: The purpose of this study was to compare CT with conventional and simulated reduced-tube current in the evaluation for acute appendicitis in children. MATERIALS AND METHODS: Validated noise-addition (tube current-reduction) software was used to create 50% and 75% tube current reductions in 60 CT examinations performed for suspected appendicitis, resulting in 180 image sets. Three blinded pediatric radiologists scored the randomized studies for the following factors: presence of the normal appendix or appendicitis (5-point scale; 1=definitely absent and 5=definitely present), presence of alternate diagnoses, and overall image quality (1=nondiagnostic and 5=excellent). Truth was defined by the interpretation of the conventional examination. RESULTS: For conventional examinations, the total number of reviews (60 cases×3 readers=180) in which the normal appendix was identified was 120 of 180 (66.7%), compared with 108 of 180 (60%) in the 50% (p=0.19) and 91 of 180 (50.6%) in the 75% (p=0.002) tube current-reduction groups. Appendicitis was identified in a total of 39 of 180 (21.7%), 38 of 180 (21.1%), and 37 of 180 (20.6%) examinations, respectively (p>0.05). This translates to sensitivities of 97% and 95% for the 50% and 75% tube current-reduction groups, respectively. Alternate diagnoses were detected in 14%, 16%, and 13% of scans, respectively. Compared with conventional-tube current examinations, reader confidence and assessment of image quality were significantly decreased for both tube current-reduction groups. CONCLUSION: Simulated tube current-reduction technology provides for systematic evaluation of diagnostic thresholds. Application of this technology in the setting of suspected appendicitis shows that tube current can be reduced by at least 50% without significantly affecting diagnostic quality, despite a decrease in reader confidence and assessment of image quality.

Authors
Swanick, CW; Gaca, AM; Hollingsworth, CL; Maxfield, CM; Li, X; Samei, E; Paulson, EK; McCarthy, MB; Frush, DP
MLA Citation
Swanick, CW, Gaca, AM, Hollingsworth, CL, Maxfield, CM, Li, X, Samei, E, Paulson, EK, McCarthy, MB, and Frush, DP. "Comparison of conventional and simulated reduced-tube current MDCT for evaluation of suspected appendicitis in the pediatric population." AJR Am J Roentgenol 201.3 (September 2013): 651-658.
PMID
23971460
Source
pubmed
Published In
AJR. American journal of roentgenology
Volume
201
Issue
3
Publish Date
2013
Start Page
651
End Page
658
DOI
10.2214/AJR.12.9667

Effective DQE (eDQE) for monoscopic and stereoscopic chest radiography imaging systems with the incorporation of anatomical noise.

PURPOSE: Stereoscopic chest biplane correlation imaging (stereo∕BCI) has been proposed as an alternative modality to single view chest x-ray (CXR). The metrics effective modulation transfer function (eMTF), effective normalized noise power spectrum (eNNPS), and effective detective quantum efficiency (eDQE) have been proposed as clinically relevant metrics for assessing clinical system performance taking into consideration the magnification and scatter effects. This study compared the metrics eMTF, eNNPS, eDQE, and detectability index for stereo∕BCI and single view CXR under isodose conditions at two magnifications for two anthropomorphic phantoms of differing sizes. METHODS: Measurements for the eMTF were taken for two phantom sizes with an opaque edge test device using established techniques. The eNNPS was measured at two isodose conditions for two phantoms using established techniques. The scatter was measured for two phantoms using an established beam stop method. All measurements were also taken at two different magnifications with two phantoms. A geometrical phantom was used for comparison with prior results for CXR although the results for an anatomy free phantom are not expected to vary for BCI. RESULTS: Stereo∕BCI resulted in improved metrics compared to single view CXR. Results indicated that magnification can potentially improve the detection performance primarily due to the air gap which reduced scatter by ∼20%. For both phantoms, at isodose, eDQE(0) for stereo∕BCI was ∼100 times higher than that for CXR. Magnification at isodose improved eDQE(0) by ∼10 times for stereo∕BCI. Increasing the dose did not improve eDQE. The detectability index for stereo∕BCI was ∼100 times better than single view CXR for all conditions. The detectability index was also not improved with increased dose. CONCLUSIONS: The findings indicate that stereo∕BCI with magnification may improve detectability of subtle lung nodules compared to single view CXR. Results were improved with magnification for the smaller phantom but not for the larger phantom. The effective DQE and the detectability index did not improve with increasing dose.

Authors
Boyce, SJ; Choudhury, KR; Samei, E
MLA Citation
Boyce, SJ, Choudhury, KR, and Samei, E. "Effective DQE (eDQE) for monoscopic and stereoscopic chest radiography imaging systems with the incorporation of anatomical noise." Med Phys 40.9 (September 2013): 091916-.
PMID
24007167
Source
pubmed
Volume
40
Issue
9
Publish Date
2013
Start Page
091916
DOI
10.1118/1.4818060

DQE of wireless digital detectors: comparative performance with differing filtration schemes.

PURPOSE: Wireless flat panel detectors are gaining increased usage in portable medical imaging. Two such detectors were evaluated and compared with a conventional flat-panel detector using the formalism of the International Electrotechnical Commission (IEC 62220-1) for measuring modulation transfer function (MTF), normalized noise power spectrum (NNPS), and detective quantum efficiency (DQE) using two different filtration schemes. METHODS: Raw images were acquired for three image receptors (DRX-1C and DRX-1, Carestream Health; Inc., Pixium 4600, Trixell) using a radiographic system with a well-characterized output (Philips Super80 CP, Philips Healthcare). Free in-air exposures were measured using a calibrated radiation meter (Unfors Mult-O-Meter Type 407, Unfors Instruments AB). Additional aluminum filtration and a new alternative combined copper-aluminum filtration were used to conform the x ray output to IEC-specified beam quality definitions RQA5 and RQA9. Using the IEC 62220-1 formalism, each detector was evaluated at XN∕2, XN, and 2XN, where the normal exposure level to the detector surface (XN) was set to 8.73 μGy (1.0 mR). The prescribed edge test device was used to evaluate the MTF, while the NNPS was measured using uniform images. The DQE was then calculated from the MTF and NNPS and compared across detectors, exposures, and filtration schemes. RESULTS: The three DR systems had largely comparable MTFs with DRX-1 demonstrating lower values above 1.0 cycles∕mm. At each exposure, DRX-1C and Pixium detectors demonstrated better noise performance than that of DRX-1. Zero-frequency DQEs for DRX-1C, Pixium, and DRX-1 detectors were approximately 74%, 63%, and 38% for RQA5 and 50%, 42%, and 28% for RQA9, respectively. CONCLUSIONS: DRX-1C detector exhibited superior DQE performance compared to Pixium and DRX-1. In terms of filtration, the alternative filtration was found to provide comparable performance in terms of rank ordering of different detectors with the added convenience of being less bulky for in-the-field measurements.

Authors
Samei, E; Murphy, S; Christianson, O
MLA Citation
Samei, E, Murphy, S, and Christianson, O. "DQE of wireless digital detectors: comparative performance with differing filtration schemes." Med Phys 40.8 (August 2013): 081910-.
PMID
23927324
Source
pubmed
Volume
40
Issue
8
Publish Date
2013
Start Page
081910
DOI
10.1118/1.4813298

The effect of dose heterogeneity on radiation risk in medical imaging.

The current estimations of risk associated with medical imaging procedures rely on assessing the organ dose via direct measurements or simulation. The dose to each organ is assumed to be homogeneous. To take into account the differences in radiation sensitivities, the mean organ doses are weighted by a corresponding tissue-weighting coefficients provided by ICRP to calculate the effective dose, which has been used as a surrogate of radiation risk. However, those coefficients were derived under the assumption of a homogeneous dose distribution within each organ. That assumption is significantly violated in most medical-imaging procedures. In helical chest CT, for example, superficial organs (e.g. breasts) demonstrate a heterogeneous dose distribution, whereas organs on the peripheries of the irradiation field (e.g. liver) might possess a discontinuous dose profile. Projection radiography and mammography involve an even higher level of organ dose heterogeneity spanning up to two orders of magnitude. As such, mean dose or point measured dose values do not reflect the maximum energy deposited per unit volume of the organ. In this paper, the magnitude of the dose heterogeneity in both CT and projection X-ray imaging was reported, using Monte Carlo methods. The lung dose demonstrated factors of 1.7 and 2.2 difference between the mean and maximum dose for chest CT and radiography, respectively. The corresponding values for the liver were 1.9 and 3.5. For mammography and breast tomosynthesis, the difference between mean glandular dose and maximum glandular dose was 3.1. Risk models based on the mean dose were found to provide a reasonable reflection of cancer risk. However, for leukaemia, they were found to significantly under-represent the risk when the organ dose distribution is heterogeneous. A systematic study is needed to develop a risk model for heterogeneous dose distributions.

Authors
Samei, E; Li, X; Chen, B; Reiman, R
MLA Citation
Samei, E, Li, X, Chen, B, and Reiman, R. "The effect of dose heterogeneity on radiation risk in medical imaging." Radiat Prot Dosimetry 155.1 (June 2013): 42-58.
PMID
23118440
Source
pubmed
Published In
Radiation Protection Dosimetry
Volume
155
Issue
1
Publish Date
2013
Start Page
42
End Page
58
DOI
10.1093/rpd/ncs275

Precision of iodine quantification in hepatic CT: effects of iterative reconstruction with various imaging parameters.

OBJECTIVE: The objective of this study was to evaluate the feasibility of using iterative reconstructions in hepatic CT to improve the precision of Hounsfield unit quantification, which is the degree to which repeated measurements under unchanged conditions provide consistent results. MATERIALS AND METHODS: An anthropomorphic liver phantom with iodinated lesions designed to simulate the enhancement of hypervascular tumors during the late hepatic arterial phase was imaged, and images were reconstructed with both filtered back projection (FBP) and iterative reconstructions, such as adaptive statistical iterative reconstruction (ASIR) and model-based iterative reconstruction (MBIR). This protocol was further expanded into various dose levels, tube voltages, and slice thicknesses to investigate the effect of iterative reconstructions under all these conditions. The iodine concentrations of the lesions were quantified, with their precision calculated in terms of repeatability coefficient. RESULTS: ASIR reduced image noise by approximately 35%, and improved the quantitative precision by approximately 5%, compared with FBP. MBIR reduced noise by more than 65% and improved the precision by approximately 25% compared with the routine protocol. MBIR consistently showed better precision across a thinner slice thickness, lower tube voltage, and larger patient, achieving the target precision level at a dose lower (≥ 40%) than that of FBP. CONCLUSION: ASIR blended with 50% of FBP indicated a moderate gain in quantitative precision compared with FBP but could achieve more with a higher percentage. A higher gain was achieved by MBIR. These findings may be used to reduce the dose required for reliable quantification and may further serve as a basis for protocol optimization in terms of iodine quantification.

Authors
Chen, B; Marin, D; Richard, S; Husarik, D; Nelson, R; Samei, E
MLA Citation
Chen, B, Marin, D, Richard, S, Husarik, D, Nelson, R, and Samei, E. "Precision of iodine quantification in hepatic CT: effects of iterative reconstruction with various imaging parameters." AJR. American journal of roentgenology 200.5 (May 2013): W475-W482.
PMID
23617515
Source
epmc
Published In
AJR. American journal of roentgenology
Volume
200
Issue
5
Publish Date
2013
Start Page
W475
End Page
W482
DOI
10.2214/ajr.12.9658

Population of anatomically variable 4D XCAT adult phantoms for imaging research and optimization.

PURPOSE: The authors previously developed the 4D extended cardiac-torso (XCAT) phantom for multimodality imaging research. The XCAT consisted of highly detailed whole-body models for the standard male and female adult, including the cardiac and respiratory motions. In this work, the authors extend the XCAT beyond these reference anatomies by developing a series of anatomically variable 4D XCAT adult phantoms for imaging research, the first library of 4D computational phantoms. METHODS: The initial anatomy of each phantom was based on chest-abdomen-pelvis computed tomography data from normal patients obtained from the Duke University database. The major organs and structures for each phantom were segmented from the corresponding data and defined using nonuniform rational B-spline surfaces. To complete the body, the authors manually added on the head, arms, and legs using the original XCAT adult male and female anatomies. The structures were scaled to best match the age and anatomy of the patient. A multichannel large deformation diffeomorphic metric mapping algorithm was then used to calculate the transform from the template XCAT phantom (male or female) to the target patient model. The transform was applied to the template XCAT to fill in any unsegmented structures within the target phantom and to implement the 4D cardiac and respiratory models in the new anatomy. Each new phantom was refined by checking for anatomical accuracy via inspection of the models. RESULTS: Using these methods, the authors created a series of computerized phantoms with thousands of anatomical structures and modeling cardiac and respiratory motions. The database consists of 58 (35 male and 23 female) anatomically variable phantoms in total. Like the original XCAT, these phantoms can be combined with existing simulation packages to simulate realistic imaging data. Each new phantom contains parameterized models for the anatomy and the cardiac and respiratory motions and can, therefore, serve as a jumping point from which to create an unlimited number of 3D and 4D variations for imaging research. CONCLUSIONS: A population of phantoms that includes a range of anatomical variations representative of the public at large is needed to more closely mimic a clinical study or trial. The series of anatomically variable phantoms developed in this work provide a valuable resource for investigating 3D and 4D imaging devices and the effects of anatomy and motion in imaging. Combined with Monte Carlo simulation programs, the phantoms also provide a valuable tool to investigate patient-specific dose and image quality, and optimization for adults undergoing imaging procedures.

Authors
Segars, WP; Bond, J; Frush, J; Hon, S; Eckersley, C; Williams, CH; Feng, J; Tward, DJ; Ratnanather, JT; Miller, MI; Frush, D; Samei, E
MLA Citation
Segars, WP, Bond, J, Frush, J, Hon, S, Eckersley, C, Williams, CH, Feng, J, Tward, DJ, Ratnanather, JT, Miller, MI, Frush, D, and Samei, E. "Population of anatomically variable 4D XCAT adult phantoms for imaging research and optimization." Med Phys 40.4 (April 2013): 043701-.
PMID
23556927
Source
pubmed
Volume
40
Issue
4
Publish Date
2013
Start Page
043701
DOI
10.1118/1.4794178

Assessment of multi-directional MTF for breast tomosynthesis.

A method was developed to assess the multi-directional modulation transfer function (MTF) of breast tomosynthesis imaging systems using a sphere phantom. The method was initially developed based on a simulation dataset. Projections were simulated for a uniform voxelized breast phantom with sphere inserts using a fluence modeled from a 28 kVp beam incident upon an indirect flat-panel detector. Based on cascaded systems modeling, characteristic noise and blurring were added to each projection. The projections were reconstructed using a standard filtered backprojection technique, producing a 3D volume with an isotropic voxel size of 200 µm. ROIs that completely encompassed single spheres were extracted and conical regions were prescribed along the three major axes extending from the centroids. Pixels within the cones were used to form edge spread functions (ESFs), from which the directional MTFs were calculated. Binning size and conical range were adjusted to maximize the accuracy and to minimize the noise of the MTF. A method was further devised to remove out-of-plane artifacts from the ESF in the x-y plane. Finally, the method was applied to experimentally assess the directional MTF of a prototype tomosynthesis system. Comparisons of the sphere-based MTF along the different axes and the theoretical MTF yielded good agreement. A 30° angular cone and a 20 µm sampling were found to provide an ideal trade-off between the noise and accuracy of the measurement. The removal of artifacts in ESF yielded 'modified' MTFs that enabled a resolution-only characterization of the in-slice resolution of tomosynthesis. Drop-off frequencies in the x- and y-directional MTFs were 1.6 cycles mm(-1) and 1.5 cycles mm(-1), respectively. The presented method of separating the effective resolution and artifacts from the measured ESF was found experimentally implementable and is expected to facilitate the interpretation of MTF measurements in tomosynthesis.

Authors
Samei, E; Murphy, S; Richard, S
MLA Citation
Samei, E, Murphy, S, and Richard, S. "Assessment of multi-directional MTF for breast tomosynthesis." Phys Med Biol 58.5 (March 7, 2013): 1649-1661.
PMID
23422248
Source
pubmed
Published In
Physics in Medicine and Biology
Volume
58
Issue
5
Publish Date
2013
Start Page
1649
End Page
1661
DOI
10.1088/0031-9155/58/5/1649

A methodology for image quality evaluation of advanced CT systems.

PURPOSE: This work involved the development of a phantom-based method to quantify the performance of tube current modulation and iterative reconstruction in modern computed tomography (CT) systems. The quantification included resolution, HU accuracy, noise, and noise texture accounting for the impact of contrast, prescribed dose, reconstruction algorithm, and body size. METHODS: A 42-cm-long, 22.5-kg polyethylene phantom was designed to model four body sizes. Each size was represented by a uniform section, for the measurement of the noise-power spectrum (NPS), and a feature section containing various rods, for the measurement of HU and the task-based modulation transfer function (TTF). The phantom was scanned on a clinical CT system (GE, 750HD) using a range of tube current modulation settings (NI levels) and reconstruction methods (FBP and ASIR30). An image quality analysis program was developed to process the phantom data to calculate the targeted image quality metrics as a function of contrast, prescribed dose, and body size. RESULTS: The phantom fabrication closely followed the design specifications. In terms of tube current modulation, the tube current and resulting image noise varied as a function of phantom size as expected based on the manufacturer specification: From the 16- to 37-cm section, the HU contrast for each rod was inversely related to phantom size, and noise was relatively constant (<5% change). With iterative reconstruction, the TTF exhibited a contrast dependency with better performance for higher contrast objects. At low noise levels, TTFs of iterative reconstruction were better than those of FBP, but at higher noise, that superiority was not maintained at all contrast levels. Relative to FBP, the NPS of iterative reconstruction exhibited an ~30% decrease in magnitude and a 0.1 mm(-1) shift in the peak frequency. CONCLUSIONS: Phantom and image quality analysis software were created for assessing CT image quality over a range of contrasts, doses, and body sizes. The testing platform enabled robust NPS, TTF, HU, and pixel noise measurements as a function of body size capable of characterizing the performance of reconstruction algorithms and tube current modulation techniques.

Authors
Wilson, JM; Christianson, OI; Richard, S; Samei, E
MLA Citation
Wilson, JM, Christianson, OI, Richard, S, and Samei, E. "A methodology for image quality evaluation of advanced CT systems." Med Phys 40.3 (March 2013): 031908-.
PMID
23464323
Source
pubmed
Volume
40
Issue
3
Publish Date
2013
Start Page
031908
DOI
10.1118/1.4791645

Relating noise to image quality indicators in CT examinations with tube current modulation.

OBJECTIVE: Modern CT systems use surrogates of noise-noise index (NI) and quality reference effective tube current-time product (Q)-to infer the quality of images acquired using tube current modulation. This study aimed to determine the relationship between actual noise and these surrogates for two CT scanners from two different manufacturers. MATERIALS AND METHODS: Two phantoms (adult and 1-year-old child) were imaged on two CT scanners (64 and 128 MDCT) using a clinical range of NI (6-22) and Q (30-300 mA). Each scan was performed twice, and noise was measured in the mediastinum, lung, and abdomen using an image subtraction technique. The effect on noise from changing other imaging parameters, such as beam collimation, pitch, peak kilovoltage, slice thickness, FOV, reconstruction kernel or algorithm, and patient age category (adult or pediatric), was investigated. RESULTS: On the 64-MDCT scanner, noise increased linearly along with NI, with the slope affected by changing the anatomy of interest, peak kilovoltage, reconstruction algorithm, and convolution kernel. The noise-NI relationship was independent of phantom size, slice thickness, pitch, FOV, and beam width. On the 128-MDCT scanner, noise decreased nonlinearly along with increasing Q, slice thickness, and peak tube voltage. The noise-Q relationship also depended on anatomy of interest, phantom size, age selection, and reconstruction algorithm but was independent of pitch, FOV, and detector configuration. CONCLUSION: We established how noise changes with changing image quality indicators across a clinically relevant range of imaging parameters. This work can aid in optimizing protocols by targeting specific noise levels for different types of CT examinations.

Authors
Solomon, JB; Li, X; Samei, E
MLA Citation
Solomon, JB, Li, X, and Samei, E. "Relating noise to image quality indicators in CT examinations with tube current modulation." AJR Am J Roentgenol 200.3 (March 2013): 592-600.
PMID
23436849
Source
pubmed
Published In
AJR. American journal of roentgenology
Volume
200
Issue
3
Publish Date
2013
Start Page
592
End Page
600
DOI
10.2214/AJR.12.8580

Preliminary evaluation of biplane correlation (BCI) stereographic imaging for lung nodule detection.

A biplane correlation (BCI) imaging system obtains images that can be viewed in stereo, thereby minimizing overlapping structures. This study investigated whether using stereoscopic visualization provides superior lung nodule detection compared to standard postero-anterior (PA) image display. Images were acquired at two oblique views of ±3° as well as at a standard PA position from 60 patients. Images were processed using optimal parameters and displayed on a stereoscopic display. The PA image was viewed in the standard format, while the oblique views were paired to provide a stereoscopic view of the subject. A preliminary observer study was performed with four radiologists who viewed and scored the PA image then viewed and scored the BCI stereoscopic image. The BCI stereoscopic viewing of lung nodules resulted in 71 % sensitivity and 0.31 positive predictive value (PPV) index compared to PA results of 86 % sensitivity and 0.26 PPV index. The sensitivity for lung nodule detection with the BCI stereoscopic system was reduced by 15 %; however, the total number of false positives reported was reduced by 35 % resulting in an improved PPV index of 20 %. The preliminary results indicate observer dependency in terms of relative advantage of either system in the detection of lung nodules, but overall equivalency of the two methods with promising potential for BCI as an adjunct diagnostic technique.

Authors
Boyce, SJ; McAdams, HP; Ravin, CE; Patz, EF; Washington, L; Martinez, S; Koweek, L; Samei, E
MLA Citation
Boyce, SJ, McAdams, HP, Ravin, CE, Patz, EF, Washington, L, Martinez, S, Koweek, L, and Samei, E. "Preliminary evaluation of biplane correlation (BCI) stereographic imaging for lung nodule detection." J Digit Imaging 26.1 (February 2013): 109-114.
PMID
22422436
Source
pubmed
Published In
Journal of Digital Imaging
Volume
26
Issue
1
Publish Date
2013
Start Page
109
End Page
114
DOI
10.1007/s10278-012-9466-6

Evaluation of two objective methods to optimize kVp and personnel exposure using a digital indirect flat panel detector and simulated veterinary patients.

It is important to optimize digital radiographic technique settings for small animal imaging in order to maximize image quality while minimizing radiation exposure to personnel. The purpose of this study was to evaluate two objective methods for determining optimal kVp values for an indirect flat panel digital detector. One method considered both image quality and personnel exposure as endpoints and one considered only image quality. Phantoms simulated veterinary patients of varying thicknesses with lesions of varying sizes. Phantoms were exposed to a range of kVp values (60, 81, 100, and 121), using different mAs settings for each phantom. Additionally, all phantoms were exposed to a standard test exposure of 100 kVp/2.5 mAs. Scattered radiation was recorded and used as a measure of personnel exposure. When personnel exposure was considered, a figure of merit was calculated as an endpoint of optimization. The optimal kVp value for each phantom was determined based on the highest signal difference-to-noise ratio with or without inclusion of the figure of merit. When personnel exposure was not considered, increasing kVp resulted in higher signal difference-to-noise ratios and personnel exposure increased when both patient thickness and kVp increased. Findings indicated that a single standard technique of 100 kVp/2.5 mAs was only optimal for most medium-sized patients. Images of thinner patients should be made with a lower kVp. Very large patients require a higher kVp than 100 regardless of the optimization method used. Personnel exposure from optimized techniques was low and not expected to exceed annual occupational dose limits.

Authors
Copple, C; Robertson, ID; Thrall, DE; Samei, E
MLA Citation
Copple, C, Robertson, ID, Thrall, DE, and Samei, E. "Evaluation of two objective methods to optimize kVp and personnel exposure using a digital indirect flat panel detector and simulated veterinary patients." Vet Radiol Ultrasound 54.1 (January 2013): 9-16.
PMID
23293957
Source
pubmed
Published In
Veterinary Radiology & Ultrasound
Volume
54
Issue
1
Publish Date
2013
Start Page
9
End Page
16
DOI
10.1111/j.1740-8261.2012.01989.x

Preliminary evaluation of biplane correlation (BCI) stereographic imaging for lung nodule detection

A biplane correlation (BCI) imaging system obtains images that can be viewed in stereo, thereby minimizing overlapping structures. This study investigated whether using stereoscopic visualization provides superior lung nodule detection compared to standard postero-anterior (PA) image display. Images were acquired at two oblique views of ±3 as well as at a standard PA position from 60 patients. Images were processed using optimal parameters and displayed on a stereoscopic display. The PA image was viewed in the standard format, while the oblique views were paired to provide a stereoscopic view of the subject. A preliminary observer study was performed with four radiologists who viewed and scored the PA image then viewed and scored the BCI stereoscopic image. The BCI stereoscopic viewing of lung nodules resulted in 71 % sensitivity and 0.31 positive predictive value (PPV) index compared to PA results of 86 % sensitivity and 0.26 PPV index. The sensitivity for lung nodule detection with the BCI stereoscopic system was reduced by 15 %; however, the total number of false positives reported was reduced by 35 % resulting in an improved PPV index of 20 %. The preliminary results indicate observer dependency in terms of relative advantage of either system in the detection of lung nodules, but overall equivalency of the two methods with promising potential for BCI as an adjunct diagnostic technique. © 2012 Society for Imaging Informatics in Medicine.

Authors
Boyce, SJ; McAdams, HP; Ravin, CE; Jr, EFP; Washington, L; Martinez, S; Koweek, L; Samei, E
MLA Citation
Boyce, SJ, McAdams, HP, Ravin, CE, Jr, EFP, Washington, L, Martinez, S, Koweek, L, and Samei, E. "Preliminary evaluation of biplane correlation (BCI) stereographic imaging for lung nodule detection." Journal of Digital Imaging 26.1 (2013): 109-114.
Source
scival
Published In
Journal of Digital Imaging
Volume
26
Issue
1
Publish Date
2013
Start Page
109
End Page
114
DOI
10.1007/s10278-012-9466-6

Monte-Carlo simulations of a coded-aperture X-ray scatter imaging system for molecular imaging

In this work, we demonstrate the ability to determine the material composition of a sample by measuring coherent scatter diffraction patterns generated using a coded-aperture x-ray scatter imaging (CAXSI) system. Most materials are known to exhibit unique diffraction patterns through coherent scattering of low-energy x-rays. However, clinical x-ray imagers typically discard scatter radiation as noise that degrades image quality. Through the addition of a coded aperture, the system can be sensitized to coherent scattered photons that carry information about the identity and location of the scattering material. In this work, we demonstrate this process using a Monte-Carlo simulation of a CAXSI system. A simulation of a CAXSI system was developed in GEANT4 with modified physics libraries to model coherent scatter diffraction patterns in materials. Simulated images were generated from 10 materials including plastics, hydrocarbons, and biological tissue. The materials were irradiated using collimated pencil- and fan-beams with energies of 160 kVp. The diffraction patterns were imaged using a simulated 2D detector and mathematically deconstructed using an analytical projection model that accounted for the known x-ray source spectrum. The deconstructed diffraction patterns were then matched with a library of known coherent scatter form-factors of different materials to determine the identity of the scatterer at different locations in the object. The results showed good agreement between the measured and known scatter patterns from the materials, demonstrating the ability to image and identify materials at different 3D locations within an object using a projection-based CAXSI system. © 2013 SPIE.

Authors
Kapadia, AJ; Lakshmanan, MN; Krishnamurthy, K; Sahbaee, P; Chawla, A; Wolter, S; Maccabe, K; Brady, D; Samei, E
MLA Citation
Kapadia, AJ, Lakshmanan, MN, Krishnamurthy, K, Sahbaee, P, Chawla, A, Wolter, S, Maccabe, K, Brady, D, and Samei, E. "Monte-Carlo simulations of a coded-aperture X-ray scatter imaging system for molecular imaging." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 8668 (2013).
Source
scival
Published In
Proceedings of SPIE
Volume
8668
Publish Date
2013
DOI
10.1117/12.2008484

Development of matched virtual and physical breast phantoms based on patient data

Physical phantoms are essential for the development, optimization, and clinical evaluation of x-ray systems. These phantoms are used for various tests such as quality assurance testing, system characterization, reconstruction evaluation, and dosimetry. They should ideally be capable of serving as ground truth for purposes such as virtual clinical trials. Currently, there is no anthropomorphic 3D physical phantom commercially available. We present our development of a new suite of physical breast phantoms based on real patient data. The phantoms were generated from the NURBS-based extended cardiac-torso (XCAT) breast phantoms, which were segmented from patient dedicated breast computed tomography data. High-resolution multi-material 3D printing technology was used to fabricate the physical models. Glandular tissue and skin were presented by the most radiographically dense photopolymer available to the printer, mimicking a 75% glandular tissue. Adipose tissue was presented by the least radiographically dense photopolymer, mimicking a 35% glandular tissue. The glandular equivalency was measured by comparing x-ray images of samples of the photopolymers available to the printer with those of breast tissue-equivalent materials. The mammographic projections and tomosynthesis reconstructed images of fabricated models showed great improvement over available phantoms, presenting a more realistic breast background. © 2013 SPIE.

Authors
Kiarashi, N; Sturgeon, GM; Nolte, LW; Lo, JY; III, JTD; Segars, WP; Samei, E
MLA Citation
Kiarashi, N, Sturgeon, GM, Nolte, LW, Lo, JY, III, JTD, Segars, WP, and Samei, E. "Development of matched virtual and physical breast phantoms based on patient data." 2013.
Source
scival
Published In
Proceedings of SPIE
Volume
8668
Publish Date
2013
DOI
10.1117/12.2008406

Estimating breast density with dual energy mammography: A simple model based on calibration phantoms

Dual energy digital mammography has been used to suppress specific breast tissue, primarily for the purpose of iodine contrast-enhanced imaging. Another application of dual energy digital mammography is to estimate breast density, as defined by the fraction of glandular tissue, by suppressing adipose tissue. Adipose equivalent phantoms were used to derive the weighting factor for dual energy subtraction at 2, 4, 6, and 8 cm thickness. For each thickness besides 8 cm, measurements were taken over a range of densities (0, 50, and 100%) and used for calibration measurements to model a density map. Once the density map was verified with uniform slabs, the density map was evaluated with 50/50 CIRS 020 phantom at 2, 4, and 6 cm thickness and demonstrated the feasibility of using dual energy subtraction to estimate breast density on complex phantoms. © 2013 SPIE.

Authors
Chung, H; Ikejimba, L; Kiarashi, N; Samei, E; Hoernig, M; Lo, JY
MLA Citation
Chung, H, Ikejimba, L, Kiarashi, N, Samei, E, Hoernig, M, and Lo, JY. "Estimating breast density with dual energy mammography: A simple model based on calibration phantoms." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 8668 (2013).
Source
scival
Published In
Proceedings of SPIE
Volume
8668
Publish Date
2013
DOI
10.1117/12.2008398

Organ dose in chest CT: Effect of modulation scheme on estimation accuracy

The purpose of this study was to evaluate how different implementations of the tube current modulation (TCM) technology affect organ dose conversion factors in chest CT and how organ dose can be accurately estimated for various modulation schemes. Computational phantom of a normal-weight female patient was used. A method was developed to generate tube current (mA) modulation profiles based on the attenuation of the phantom, taking into account the geometry of the CT system as well as the x-ray energy spectrum and bowtie filtration in a CT scan. The mA for a given projection angle was calculated as a power-law function of the attenuation along this projection. The exponent of this function, termed modulation control strength, was varied from 0 to 1 to emulate the effects of different TCM schemes. Organ dose was estimated for a chest scan for each modulation scheme and was subsequently normalized by volume-weighted CT dose index (CTDIvol) to obtain conversion factors. The results showed that the conversion factors are second-order polynomial functions of the modulation control strength. The conversion factors established for a fixed-mA scan may be used to estimate organ dose in a TCM scan. For organs on the periphery of the scan coverage, the best accuracy is achieved when using CTDIvol computed from the average mA of the entire scan. For organs inside the scan coverage, the best accuracy is achieved when using CTDIvol computed from the volume-averaged mA values of all the axial slices containing the organ. © 2013 SPIE.

Authors
Li, X; Segars, WP; Samei, E
MLA Citation
Li, X, Segars, WP, and Samei, E. "Organ dose in chest CT: Effect of modulation scheme on estimation accuracy." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 8668 (2013).
Source
scival
Published In
Proceedings of SPIE
Volume
8668
Publish Date
2013
DOI
10.1117/12.2008505

Comparative dosimetry of radiography, tomosynthesis, and CT for chest imaging across 59 adult patients

There are three main x-ray based modalities for imaging the thorax: radiography, tomosynthesis, and CT. CT provides perhaps the highest level of feature resolution but at notably higher radiation dose. To implement the ALARA (as low as reasonable achievable) principle in making an appropriate choice between standard chest projection imaging, tomosynthesis, and CT to achieve the lowest possible dose to patients, the effective doses and risk indices for each modality should be accurately known. In this study, we employed 59 computational anthropomorphic male and female extended cardiac-torso (XCAT) adult phantoms and a Monte Carlo simulation program (PENELOPE, version 2006, Universitat de Barcelona, Spain). Effective dose and risk index was estimated for a clinical radiography system enabling to conduct chest radiography and tomosynthesis sweep (Definium 8000, Volume RAD, GE Healthcare) and a clinical CT system (LightSpeed VCT, GE Healthcare). It was found that the absolute effective dose and risk index increased greatly with increasing patient size for CT, while these two dose metrics only increased slightly for radiography and tomosynthesis. This suggests that it is important to specify patient size when comparing radiation dose across imaging modalities. © 2013 SPIE.

Authors
Zhang, Y; Li, X; Segars, WP; Samei, E
MLA Citation
Zhang, Y, Li, X, Segars, WP, and Samei, E. "Comparative dosimetry of radiography, tomosynthesis, and CT for chest imaging across 59 adult patients." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 8668 (2013).
Source
scival
Published In
Proceedings of SPIE
Volume
8668
Publish Date
2013
DOI
10.1117/12.2008544

Projection-based Dose Metric: Accuracy Testing and Applications for CT Design

Authors
Tian, X; Yin, Z; De Man, B; Samei, E
MLA Citation
Tian, X, Yin, Z, De Man, B, and Samei, E. "Projection-based Dose Metric: Accuracy Testing and Applications for CT Design." 2013.
Source
wos-lite
Published In
Proceedings of SPIE - The International Society for Optical Engineering
Volume
8668
Publish Date
2013
DOI
10.1117/12.2008051

Development of a phantom-based methodology for the assessment of quantification performance in CT

Authors
Chen, B; Samei, E
MLA Citation
Chen, B, and Samei, E. "Development of a phantom-based methodology for the assessment of quantification performance in CT." 2013.
Source
wos-lite
Published In
Proceedings of SPIE - The International Society for Optical Engineering
Volume
8668
Publish Date
2013
DOI
10.1117/12.2008481

Are Uniform Phantoms Sufficient to Characterize the Performance of Iterative Reconstruction in CT?

Authors
Solomon, J; Samei, E
MLA Citation
Solomon, J, and Samei, E. "Are Uniform Phantoms Sufficient to Characterize the Performance of Iterative Reconstruction in CT?." 2013.
Source
wos-lite
Published In
Proceedings of SPIE - The International Society for Optical Engineering
Volume
8668
Publish Date
2013
DOI
10.1117/12.2008378

Simulation of Anatomical Texture in Voxelized XCAT Phantoms

Authors
Bond, J; Frush, D; Samei, E; Segars, WP
MLA Citation
Bond, J, Frush, D, Samei, E, and Segars, WP. "Simulation of Anatomical Texture in Voxelized XCAT Phantoms." 2013.
Source
wos-lite
Published In
Proceedings of SPIE - The International Society for Optical Engineering
Volume
8668
Publish Date
2013
DOI
10.1117/12.2008422

Effects of protocol and obesity on dose conversion factors in adult body CT.

PURPOSE: In computed tomography (CT), organ dose, effective dose, and risk index can be estimated from volume-weighted CT dose index (CTDI(vol)) or dose-length product (DLP) using conversion coefficients. Studies have investigated how these coefficients vary across scanner models, scan parameters, and patient size. However, their variability across CT protocols has not been systematically studied. Furthermore, earlier studies of the effect of patient size have not included obese individuals, which currently represent more than one-third of U.S. adults. The purpose of this study was to assess the effects of protocol and obesity on dose and risk conversion coefficients in adult body CT. METHODS: Whole-body computational phantoms were created from clinical CT images of six adult patients (three males, three females), representing normal-weight patients and patients of three obesity classes. Body CT protocols at our institution were selected and categorized into ten examination categories based on anatomical region examined. A validated Monte Carlo program was used to estimate organ dose. Organ dose estimates were normalized by CTDI(vol) and size-specific dose estimate (SSDE) to obtain organ dose conversion coefficients (denoted as h and h(ss) factors, respectively). Assuming each phantom to be 20, 40, and 60 years old, effective dose and risk index were calculated and normalized by DLP to obtain effective dose and risk index conversion coefficients (denoted as k and q factors, respectively). Coefficient of variation was used to quantify the variability of each conversion coefficient across examination categories. The effect of obesity was assessed by comparing each obese phantom with the normal-weight phantom of the same gender. RESULTS: For a given organ, the variability of h factor across examination categories that encompassed the entire organ volume was generally within 15%. However, k factor varied more across examination categories (15%-27%). For all three ages, the variability of q factor was small for male (<10%), but large for female phantoms (21%-43%). Relative to the normal-weight phantoms, the reduction in h factor (an average across fully encompassed organs) was 17%-42%, 17%-40%, and 51%-63% for obese-class-I, obese-class-II, and obese-class-III phantoms, respectively. h(ss) factor was not independent of patient diameter and generally decreased with increasing obesity. Relative to the normal-weight phantoms, the reduction in k factor was 12%-40%, 14%-46%, and 44%-59% for obese-class-I, obese-class-II, and obese-class-III phantoms, respectively. The respective reduction in q factor was 11%-36%, 17%-42%, and 48%-59% at 20 years of age and similar at other ages. CONCLUSIONS: In adult body CT, dose to an organ fully encompassed by the primary radiation beam can be estimated from CTDI(vol) using a protocol-independent conversion coefficient. However, fully encompassed organs only account for 50% ± 19% of k factor and 46% ± 24% of q factor. Dose received by partially encompassed organs is also substantial. To estimate effective dose and risk index from DLP, it is necessary to use conversion coefficients specific to the anatomical region examined. Obesity has a significant effect on dose and risk conversion coefficients, which cannot be predicted using body diameter alone. SSDE-normalized organ dose is not independent of diameter. SSDE itself generally overestimates organ dose for obese patients.

Authors
Li, X; Samei, E; Williams, CH; Segars, WP; Tward, DJ; Miller, MI; Ratnanather, JT; Paulson, EK; Frush, DP
MLA Citation
Li, X, Samei, E, Williams, CH, Segars, WP, Tward, DJ, Miller, MI, Ratnanather, JT, Paulson, EK, and Frush, DP. "Effects of protocol and obesity on dose conversion factors in adult body CT." Med Phys 39.11 (November 2012): 6550-6571.
PMID
23127050
Source
pubmed
Published In
Medical physics
Volume
39
Issue
11
Publish Date
2012
Start Page
6550
End Page
6571
DOI
10.1118/1.4754584

An image-based technique to assess the perceptual quality of clinical chest radiographs.

PURPOSE: Current clinical image quality assessment techniques mainly analyze image quality for the imaging system in terms of factors such as the capture system modulation transfer function, noise power spectrum, detective quantum efficiency, and the exposure technique. While these elements form the basic underlying components of image quality, when assessing a clinical image, radiologists seldom refer to these factors, but rather examine several specific regions of the displayed patient images, further impacted by a particular image processing method applied, to see whether the image is suitable for diagnosis. In this paper, the authors developed a novel strategy to simulate radiologists' perceptual evaluation process on actual clinical chest images. METHODS: Ten regional based perceptual attributes of chest radiographs were determined through an observer study. Those included lung grey level, lung detail, lung noise, rib-lung contrast, rib sharpness, mediastinum detail, mediastinum noise, mediastinum alignment, subdiaphragm-lung contrast, and subdiaphragm area. Each attribute was characterized in terms of a physical quantity measured from the image algorithmically using an automated process. A pilot observer study was performed on 333 digital chest radiographs, which included 179 PA images with 10:1 ratio grids (set 1) and 154 AP images without grids (set 2), to ascertain the correlation between image perceptual attributes and physical quantitative measurements. To determine the acceptable range of each perceptual attribute, a preliminary quality consistency range was defined based on the preferred 80% of images in set 1. Mean value difference (μ(1) - μ(2)) and variance ratio (σ(1) (2)/σ(2) (2)) were investigated to further quantify the differences between the selected two image sets. RESULTS: The pilot observer study demonstrated that our regional based physical quantity metrics of chest radiographs correlated very well with their corresponding perceptual attributes. The distribution comparisons, mean value difference estimations, and variance ratio estimations of each physical quantity between sets of images from two different techniques matched our expectation that the image quality of set 1 should be better than that of set 2. CONCLUSIONS: The measured physical quantities provide a robust reflection of perceptual image quality in clinical images. The methodology can be readily applied for automated evaluation of perceptual image quality in clinical chest radiographs.

Authors
Lin, Y; Luo, H; Dobbins, JT; Page McAdams, H; Wang, X; Sehnert, WJ; Barski, L; Foos, DH; Samei, E
MLA Citation
Lin, Y, Luo, H, Dobbins, JT, Page McAdams, H, Wang, X, Sehnert, WJ, Barski, L, Foos, DH, and Samei, E. "An image-based technique to assess the perceptual quality of clinical chest radiographs." Med Phys 39.11 (November 2012): 7019-7031.
PMID
23127093
Source
pubmed
Published In
Medical physics
Volume
39
Issue
11
Publish Date
2012
Start Page
7019
End Page
7031
DOI
10.1118/1.4760886

Automated size-specific CT dose monitoring program: assessing variability in CT dose.

PURPOSE: The potential health risks associated with low levels of ionizing radiation have created a movement in the radiology community to optimize computed tomography (CT) imaging protocols to use the lowest radiation dose possible without compromising the diagnostic usefulness of the images. Despite efforts to use appropriate and consistent radiation doses, studies suggest that a great deal of variability in radiation dose exists both within and between institutions for CT imaging. In this context, the authors have developed an automated size-specific radiation dose monitoring program for CT and used this program to assess variability in size-adjusted effective dose from CT imaging. METHODS: The authors radiation dose monitoring program operates on an independent health insurance portability and accountability act compliant dosimetry server. Digital imaging and communication in medicine routing software is used to isolate dose report screen captures and scout images for all incoming CT studies. Effective dose conversion factors (k-factors) are determined based on the protocol and optical character recognition is used to extract the CT dose index and dose-length product. The patient's thickness is obtained by applying an adaptive thresholding algorithm to the scout images and is used to calculate the size-adjusted effective dose (ED(adj)). The radiation dose monitoring program was used to collect data on 6351 CT studies from three scanner models (GE Lightspeed Pro 16, GE Lightspeed VCT, and GE Definition CT750 HD) and two institutions over a one-month period and to analyze the variability in ED(adj) between scanner models and across institutions. RESULTS: No significant difference was found between computer measurements of patient thickness and observer measurements (p = 0.17), and the average difference between the two methods was less than 4%. Applying the size correction resulted in ED(adj) that differed by up to 44% from effective dose estimates that were not adjusted by patient size. Additionally, considerable differences were noted in ED(adj) distributions between scanners, with scanners employing iterative reconstruction exhibiting significantly lower ED(adj) (range: 9%-64%). Finally, a significant difference (up to 59%) in ED(adj) distributions was observed between institutions, indicating the potential for dose reduction. CONCLUSIONS: The authors developed a robust automated size-specific radiation dose monitoring program for CT. Using this program, significant differences in ED(adj) were observed between scanner models and across institutions. This new dose monitoring program offers a unique tool for improving quality assurance and standardization both within and across institutions.

Authors
Christianson, O; Li, X; Frush, D; Samei, E
MLA Citation
Christianson, O, Li, X, Frush, D, and Samei, E. "Automated size-specific CT dose monitoring program: assessing variability in CT dose." Med Phys 39.11 (November 2012): 7131-7139.
PMID
23127104
Source
pubmed
Published In
Medical physics
Volume
39
Issue
11
Publish Date
2012
Start Page
7131
End Page
7139
DOI
10.1118/1.4761871

Quantitative comparison of noise texture across CT scanners from different manufacturers.

PURPOSE: To quantitatively compare noise texture across computed tomography (CT) scanners from different manufacturers using the noise power spectrum (NPS). METHODS: The American College of Radiology CT accreditation phantom (Gammex 464, Gammex, Inc., Middleton, WI) was imaged on two scanners: Discovery CT 750HD (GE Healthcare, Waukesha, WI), and SOMATOM Definition Flash (Siemens Healthcare, Germany), using a consistent acquisition protocol (120 kVp, 0.625∕0.6 mm slice thickness, 250 mAs, and 22 cm field of view). Images were reconstructed using filtered backprojection and a wide selection of reconstruction kernels. For each image set, the 2D NPS were estimated from the uniform section of the phantom. The 2D spectra were normalized by their integral value, radially averaged, and filtered by the human visual response function. A systematic kernel-by-kernel comparison across manufacturers was performed by computing the root mean square difference (RMSD) and the peak frequency difference (PFD) between the NPS from different kernels. GE and Siemens kernels were compared and kernel pairs that minimized the RMSD and |PFD| were identified. RESULTS: The RMSD (|PFD|) values between the NPS of GE and Siemens kernels varied from 0.01 mm(2) (0.002 mm(-1)) to 0.29 mm(2) (0.74 mm(-1)). The GE kernels "Soft," "Standard," "Chest," and "Lung" closely matched the Siemens kernels "B35f," "B43f," "B41f," and "B80f" (RMSD < 0.05 mm(2), |PFD| < 0.02 mm(-1), respectively). The GE "Bone," "Bone+," and "Edge" kernels all matched most closely with Siemens "B75f" kernel but with sizeable RMSD and |PFD| values up to 0.18 mm(2) and 0.41 mm(-1), respectively. These sizeable RMSD and |PFD| values corresponded to visually perceivable differences in the noise texture of the images. CONCLUSIONS: It is possible to use the NPS to quantitatively compare noise texture across CT systems. The degree to which similar texture across scanners could be achieved varies and is limited by the kernels available on each scanner.

Authors
Solomon, JB; Christianson, O; Samei, E
MLA Citation
Solomon, JB, Christianson, O, and Samei, E. "Quantitative comparison of noise texture across CT scanners from different manufacturers." Med Phys 39.10 (October 2012): 6048-6055.
PMID
23039643
Source
pubmed
Published In
Medical physics
Volume
39
Issue
10
Publish Date
2012
Start Page
6048
End Page
6055
DOI
10.1118/1.4752209

Gray-scale inversion radiographic display for the detection of pulmonary nodules on chest radiographs.

The purpose of this study was to investigate gray-scale inversion in nodule detection on chest radiography. Simulated nodules were superimposed randomly onto normal chest radiographs. Six radiologists interpreted 144 chest radiographs during three reading sessions: traditional presentation, inverted gray-scale, and a choice session allowing use of traditional and gray-scale inverted views. Sensitivity and specificity were used to assess accuracy based on presence or absence of a nodule. Gray-scale inversion and choice display sessions resulted in significantly higher nodule detection specificity and decreased sensitivity compared to traditional display. Gray-scale inversion may decrease false-positive nodule findings during chest X-ray interpretation.

Authors
Lungren, MP; Samei, E; Barnhart, H; McAdams, HP; Leder, RA; Christensen, JD; Wylie, JD; Tan, JW; Li, X; Hurwitz, LM
MLA Citation
Lungren, MP, Samei, E, Barnhart, H, McAdams, HP, Leder, RA, Christensen, JD, Wylie, JD, Tan, JW, Li, X, and Hurwitz, LM. "Gray-scale inversion radiographic display for the detection of pulmonary nodules on chest radiographs." Clin Imaging 36.5 (September 2012): 515-521.
PMID
22920355
Source
pubmed
Published In
Clinical Imaging
Volume
36
Issue
5
Publish Date
2012
Start Page
515
End Page
521
DOI
10.1016/j.clinimag.2012.01.009

Radiation dose reduction in abdominal computed tomography during the late hepatic arterial phase using a model-based iterative reconstruction algorithm: how low can we go?

OBJECTIVE: The aim of this study was to compare the image quality of abdominal computed tomography scans in an anthropomorphic phantom acquired at different radiation dose levels where each raw data set is reconstructed with both a standard convolution filtered back projection (FBP) and a full model-based iterative reconstruction (MBIR) algorithm. MATERIALS AND METHODS: An anthropomorphic phantom in 3 sizes was used with a custom-built liver insert simulating late hepatic arterial enhancement and containing hypervascular liver lesions of various sizes. Imaging was performed on a 64-section multidetector-row computed tomography scanner (Discovery CT750 HD; GE Healthcare, Waukesha, WI) at 3 different tube voltages for each patient size and 5 incrementally decreasing tube current-time products for each tube voltage. Quantitative analysis consisted of contrast-to-noise ratio calculations and image noise assessment. Qualitative image analysis was performed by 3 independent radiologists rating subjective image quality and lesion conspicuity. RESULTS: Contrast-to-noise ratio was significantly higher and mean image noise was significantly lower on MBIR images than on FBP images in all patient sizes, at all tube voltage settings, and all radiation dose levels (P < 0.05). Overall image quality and lesion conspicuity were rated higher for MBIR images compared with FBP images at all radiation dose levels. Image quality and lesion conspicuity on 25% to 50% dose MBIR images were rated equal to full-dose FBP images. CONCLUSION: This phantom study suggests that depending on patient size, clinically acceptable image quality of the liver in the late hepatic arterial phase can be achieved with MBIR at approximately 50% lower radiation dose compared with FBP.

Authors
Husarik, DB; Marin, D; Samei, E; Richard, S; Chen, B; Jaffe, TA; Bashir, MR; Nelson, RC
MLA Citation
Husarik, DB, Marin, D, Samei, E, Richard, S, Chen, B, Jaffe, TA, Bashir, MR, and Nelson, RC. "Radiation dose reduction in abdominal computed tomography during the late hepatic arterial phase using a model-based iterative reconstruction algorithm: how low can we go?." Invest Radiol 47.8 (August 2012): 468-474.
PMID
22717881
Source
pubmed
Published In
Investigative Radiology
Volume
47
Issue
8
Publish Date
2012
Start Page
468
End Page
474
DOI
10.1097/RLI.0b013e318251eafd

The effects of ambient lighting in chest radiology reading rooms.

Under typical dark chest radiography reading room conditions, a radiologist's pupils contract and dilate as their visual focus intermittently shifts between the high luminance monitor and the darker background wall, resulting in increased visual fatigue and degradation of diagnostic performance. A controlled increase of ambient lighting may minimize these visual adjustments and potentially improve comfort and accuracy. This study was designed to determine the effect of a controlled increase of ambient lighting on chest radiologist nodule detection performance. Four chest radiologists read 100 radiographs (50 normal and 50 containing a subtle nodule) under low (E=1 lx) and elevated (E=50 lx) ambient lighting levels on a DICOM-calibrated, medical-grade liquid crystal display. Radiologists were asked to identify nodule locations and rate their detection confidence. A receiver operating characteristic (ROC) analysis of radiologist results was performed and area under ROC curve (AUC) values calculated for each ambient lighting level. Additionally, radiologist selection times under both illuminance conditions were determined. Average AUC values did not significantly differ (p>0.05) between ambient lighting levels (estimated mean difference=-0.03; 95% CI, (-0.08, 0.03)). Average selection times decreased or remained constant with increased illuminance. The most considerable decreases occurred for false positive identification times (35.4±18.8 to 26.2±14.9 s) and true positive identification times (29.7±18.3 to 24.5±15.5 s). No performance differences were statistically significant. Study findings suggest that a controlled increase of ambient lighting within darkly lit chest radiology reading rooms, to a level more suitable for performance of common radiological tasks, does not appear to have a statistically significant effect on nodule detection performance.

Authors
Pollard, BJ; Samei, E; Chawla, AS; Beam, C; Heyneman, LE; Koweek, LMH; Martinez-Jimenez, S; Washington, L; Hashimoto, N; McAdams, HP
MLA Citation
Pollard, BJ, Samei, E, Chawla, AS, Beam, C, Heyneman, LE, Koweek, LMH, Martinez-Jimenez, S, Washington, L, Hashimoto, N, and McAdams, HP. "The effects of ambient lighting in chest radiology reading rooms." J Digit Imaging 25.4 (August 2012): 520-526.
PMID
22349990
Source
pubmed
Published In
Journal of Digital Imaging
Volume
25
Issue
4
Publish Date
2012
Start Page
520
End Page
526
DOI
10.1007/s10278-012-9459-5

Achieving routine submillisievert CT scanning: report from the summit on management of radiation dose in CT.

This Special Report presents the consensus of the Summit on Management of Radiation Dose in Computed Tomography (CT) (held in February 2011), which brought together participants from academia, clinical practice, industry, and regulatory and funding agencies to identify the steps required to reduce the effective dose from routine CT examinations to less than 1 mSv. The most promising technologies and methods discussed at the summit include innovations and developments in x-ray sources; detectors; and image reconstruction, noise reduction, and postprocessing algorithms. Access to raw projection data and standard data sets for algorithm validation and optimization is a clear need, as is the need for new, clinically relevant metrics of image quality and diagnostic performance. Current commercially available techniques such as automatic exposure control, optimization of tube potential, beam-shaping filters, and dynamic z-axis collimators are important, and education to successfully implement these methods routinely is critically needed. Other methods that are just becoming widely available, such as iterative reconstruction, noise reduction, and postprocessing algorithms, will also have an important role. Together, these existing techniques can reduce dose by a factor of two to four. Technical advances that show considerable promise for additional dose reduction but are several years or more from commercial availability include compressed sensing, volume of interest and interior tomography techniques, and photon-counting detectors. This report offers a strategic roadmap for the CT user and research and manufacturer communities toward routinely achieving effective doses of less than 1 mSv, which is well below the average annual dose from naturally occurring sources of radiation.

Authors
McCollough, CH; Chen, GH; Kalender, W; Leng, S; Samei, E; Taguchi, K; Wang, G; Yu, L; Pettigrew, RI
MLA Citation
McCollough, CH, Chen, GH, Kalender, W, Leng, S, Samei, E, Taguchi, K, Wang, G, Yu, L, and Pettigrew, RI. "Achieving routine submillisievert CT scanning: report from the summit on management of radiation dose in CT." Radiology 264.2 (August 2012): 567-580.
PMID
22692035
Source
pubmed
Published In
Radiology
Volume
264
Issue
2
Publish Date
2012
Start Page
567
End Page
580
DOI
10.1148/radiol.12112265

Towards task-based assessment of CT performance: system and object MTF across different reconstruction algorithms.

PURPOSE: To investigate a measurement method for evaluating the resolution properties of CT imaging systems across reconstruction algorithms, dose, and contrast. METHODS: An algorithm was developed to extract the task-based modulation transfer function (MTF) from disk images generated from the rod inserts in the ACR phantom (model 464 Gammex, WI). These inserts are conventionally employed for HU accuracy assessment. The edge of the disk objects was analyzed to determine the edge-spread function, which was differentiated to yield the line-spread function and Fourier-transformed to generate the object-specific MTF for task-based assessment, denoted MTF(Task). The proposed MTF measurement method was validated against the conventional wire technique and further applied to measure the MTF of CT images reconstructed with an adaptive statistical iterative algorithm (ASIR) and a model-based iterative (MBIR) algorithm. Results were further compared to the standard filtered back projection (FBP) algorithm. Measurements were performed and compared across different doses and contrast levels to ascertain the MTF(Task) dependencies on those factors. RESULTS: For the FBP reconstructed images, the MTF(Task) measured with the inserts were the same as the MTF measured from the wire-based method. For the ASIR and MBIR data, the MTF(Task) using the high contrast insert was similar to the wire-based MTF and equal or superior to that of FBP. However, results for the MTF(Task) measured using the low-contrast inserts, the MTF(Task) for ASIR and MBIR data was lower than for the FBP, which was constant throughout all measurements. Similarly, as a function of mA, the MTF(Task) for ASIR and MBIR varied as a function of noise--with MTF(Task) being proportional to mA. Overall greater variability of MTF(Task) across dose and contrast was observed for MBIR than for ASIR. CONCLUSIONS: This approach provides a method for assessing the task-based MTF of a CT system using conventional and iterative reconstructions. Results demonstrated that the object-specific MTF can vary as a function of dose and contrast. The analysis highlighted the paradigm shift for iterative reconstructions when compared to FBP, where iterative reconstructions generally offer superior noise performance but with varying resolution as a function of dose and contrast. The MTF(Task) generated by this method is expected to provide a more comprehensive assessment of image resolution across different reconstruction algorithms and imaging tasks.

Authors
Richard, S; Husarik, DB; Yadava, G; Murphy, SN; Samei, E
MLA Citation
Richard, S, Husarik, DB, Yadava, G, Murphy, SN, and Samei, E. "Towards task-based assessment of CT performance: system and object MTF across different reconstruction algorithms." Med Phys 39.7 (July 2012): 4115-4122.
PMID
22830744
Source
pubmed
Published In
Medical physics
Volume
39
Issue
7
Publish Date
2012
Start Page
4115
End Page
4122
DOI
10.1118/1.4725171

Organ doses, effective doses, and risk indices in adult CT: comparison of four types of reference phantoms across different examination protocols.

PURPOSE: Radiation exposure from computed tomography (CT) to the public has increased the concern among radiation protection professionals. Being able to accurately assess the radiation dose patients receive during CT procedures is a crucial step in the management of CT dose. Currently, various computational anthropomorphic phantoms are used to assess radiation dose by different research groups. It is desirable to better understand how the dose results are affected by different choices of phantoms. In this study, the authors assessed the uncertainties in CT dose and risk estimation associated with different types of computational phantoms for a selected group of representative CT protocols. METHODS: Routinely used CT examinations were categorized into ten body and three neurological examination categories. Organ doses, effective doses, risk indices, and conversion coefficients to effective dose and risk index (k and q factors, respectively) were estimated for these examinations for a clinical CT system (LightSpeed VCT, GE Healthcare). Four methods were used, each employing a different type of reference phantoms. The first and second methods employed a Monte Carlo program previously developed and validated in our laboratory. In the first method, the reference male and female extended cardiac-torso (XCAT) phantoms were used, which were initially created from the Visible Human data and later adjusted to match organ masses defined in ICRP publication 89. In the second method, the reference male and female phantoms described in ICRP publication 110 were used, which were initially developed from tomographic data of two patients and later modified to match ICRP 89 organ masses. The third method employed a commercial dosimetry spreadsheet (ImPACT group, London, England) with its own hermaphrodite stylized phantom. In the fourth method, another widely used dosimetry spreadsheet (CT-Expo, Medizinische Hochschule, Hannover, Germany) was employed together with its associated male and female stylized phantoms. RESULTS: For fully irradiated organs, average coefficients of variation (COV) ranged from 0.07 to 0.22 across the four male phantoms and from 0.06 to 0.18 across the four female phantoms; for partially irradiated organs, average COV ranged from 0.13 to 0.30 across the four male phantoms and from 0.15 to 0.30 across the four female phantoms. Doses to the testes, breasts, and esophagus showed large variations between phantoms. COV for gender-averaged effective dose and k factor ranged from 0.03 to 0.23 and from 0.06 to 0.30, respectively. COV for male risk index and q factor ranged from 0.06 to 0.30 and from 0.05 to 0.36, respectively; COV for female risk index and q factor ranged from 0.06 to 0.49 and from 0.07 to 0.54, respectively. CONCLUSIONS: Despite closely matched organ mass, total body weight, and height, large differences in organ dose exist due to variation in organ location, spatial distribution, and dose approximation method. Dose differences for fully irradiated radiosensitive organs were much smaller than those for partially irradiated organs. Weighted dosimetry quantities including effective dose, male risk indices, k factors, and male q factors agreed well across phantoms. The female risk indices and q factors varied considerably across phantoms.

Authors
Zhang, Y; Li, X; Segars, WP; Samei, E
MLA Citation
Zhang, Y, Li, X, Segars, WP, and Samei, E. "Organ doses, effective doses, and risk indices in adult CT: comparison of four types of reference phantoms across different examination protocols." Med Phys 39.6 (June 2012): 3404-3423.
PMID
22755721
Source
pubmed
Published In
Medical physics
Volume
39
Issue
6
Publish Date
2012
Start Page
3404
End Page
3423
DOI
10.1118/1.4718710

X-Ray Coherent Scatter Diffraction Pattern Modeling in GEANT4

Authors
Kapadia, A; Samei, E; Harrawood, B; Sahbaee, P; Chawla, A; Tan, Z; Brady, D
MLA Citation
Kapadia, A, Samei, E, Harrawood, B, Sahbaee, P, Chawla, A, Tan, Z, and Brady, D. "X-Ray Coherent Scatter Diffraction Pattern Modeling in GEANT4." June 2012.
Source
wos-lite
Published In
Medical physics
Volume
39
Issue
6
Publish Date
2012
Start Page
3642
End Page
3643

Task-Based Image Quality of CT Iterative Reconstruction Across Three Commercial Implementations

Authors
Samei, E; Christianson, O; Chen, J; Yang, Z; Saiprasad, G; Dima, A; Filliben, J; Peskin, A; Siegel, E
MLA Citation
Samei, E, Christianson, O, Chen, J, Yang, Z, Saiprasad, G, Dima, A, Filliben, J, Peskin, A, and Siegel, E. "Task-Based Image Quality of CT Iterative Reconstruction Across Three Commercial Implementations." June 2012.
Source
wos-lite
Published In
Medical physics
Volume
39
Issue
6
Publish Date
2012
Start Page
4016
End Page
4016

Evaluating the Impact of Iterative Reconstruction for Three Major CT Vendors

Authors
Chen, J; Yang, Z; Samei, E; Christianson, O; Dima, A; Filliben, J; Peskin, A; Saiprasad, G; Siegel, E
MLA Citation
Chen, J, Yang, Z, Samei, E, Christianson, O, Dima, A, Filliben, J, Peskin, A, Saiprasad, G, and Siegel, E. "Evaluating the Impact of Iterative Reconstruction for Three Major CT Vendors." June 2012.
Source
wos-lite
Published In
Medical physics
Volume
39
Issue
6
Publish Date
2012
Start Page
3605
End Page
3606

Informatics 2: Dose Monitoring

Authors
Cook, T; Christianson, O; Samei, E
MLA Citation
Cook, T, Christianson, O, and Samei, E. "Informatics 2: Dose Monitoring." June 2012.
Source
wos-lite
Published In
Medical physics
Volume
39
Issue
6
Publish Date
2012
Start Page
3917
End Page
3917

An Effective Dose Monitoring Program for Computed Radiography

Authors
Johnson, J; Samei, E; Christianson, O; Bower, D
MLA Citation
Johnson, J, Samei, E, Christianson, O, and Bower, D. "An Effective Dose Monitoring Program for Computed Radiography." June 2012.
Source
wos-lite
Published In
Medical physics
Volume
39
Issue
6
Publish Date
2012
Start Page
3607
End Page
3607

The Design of An Institution Wide Comprehensive Technique Chart for Size- Specific Radiography From Pediatrics to Adults

Authors
Bower, D; Samei, E; Johnson, J
MLA Citation
Bower, D, Samei, E, and Johnson, J. "The Design of An Institution Wide Comprehensive Technique Chart for Size- Specific Radiography From Pediatrics to Adults." June 2012.
Source
wos-lite
Published In
Medical physics
Volume
39
Issue
6
Publish Date
2012
Start Page
3608
End Page
3608

Comparison of Risks for Two Medical Imaging Procedures

Authors
Choudhury, KR; Tian, R; Li, X; Samei, E
MLA Citation
Choudhury, KR, Tian, R, Li, X, and Samei, E. "Comparison of Risks for Two Medical Imaging Procedures." June 2012.
Source
wos-lite
Published In
Medical physics
Volume
39
Issue
6
Publish Date
2012
Start Page
3635
End Page
3635

Comparison of Automated Methods to Measure Patient Size for Dose-Monitoring in Computed Tomography

Authors
Christianson, O; Frush, D; Samei, E
MLA Citation
Christianson, O, Frush, D, and Samei, E. "Comparison of Automated Methods to Measure Patient Size for Dose-Monitoring in Computed Tomography." June 2012.
Source
wos-lite
Published In
Medical physics
Volume
39
Issue
6
Publish Date
2012
Start Page
3940
End Page
3940

Defining Performance-Based, Size-Specific, Optimized Protocols for Pediatric CT

Authors
Li, X; Samei, E; Solomon, J; Frush, D
MLA Citation
Li, X, Samei, E, Solomon, J, and Frush, D. "Defining Performance-Based, Size-Specific, Optimized Protocols for Pediatric CT." June 2012.
Source
wos-lite
Published In
Medical physics
Volume
39
Issue
6
Publish Date
2012
Start Page
4014
End Page
4015

CT QA Revisited in Context of Tube Current Modulation and Iterative Reconstruction

Authors
Winslow, J; Wilson, J; Christianson, O; Samei, E
MLA Citation
Winslow, J, Wilson, J, Christianson, O, and Samei, E. "CT QA Revisited in Context of Tube Current Modulation and Iterative Reconstruction." June 2012.
Source
wos-lite
Published In
Medical physics
Volume
39
Issue
6
Publish Date
2012
Start Page
3606
End Page
3606

Limits of Dose Reduction in CT: Where Are They and How Will We Know When We Get There?

Authors
McNitt-Gray, M; Noo, F; Fessler, J; Samei, E
MLA Citation
McNitt-Gray, M, Noo, F, Fessler, J, and Samei, E. "Limits of Dose Reduction in CT: Where Are They and How Will We Know When We Get There?." June 2012.
Source
wos-lite
Published In
Medical physics
Volume
39
Issue
6
Publish Date
2012
Start Page
3868
End Page
3868

Quantitative Comparison of Noise Texture Across CT Scanners From Different Vendors

Authors
Solomon, J; Christianson, O; Samei, E
MLA Citation
Solomon, J, Christianson, O, and Samei, E. "Quantitative Comparison of Noise Texture Across CT Scanners From Different Vendors." June 2012.
Source
wos-lite
Published In
Medical physics
Volume
39
Issue
6
Publish Date
2012
Start Page
4016
End Page
4016

MA Modulation and Iterative Reconstruction: Evaluation Using a New CT Phantom

Authors
Wilson, JM; Christianson, O; Chen, B; Winslow, J; Samei, E
MLA Citation
Wilson, JM, Christianson, O, Chen, B, Winslow, J, and Samei, E. "MA Modulation and Iterative Reconstruction: Evaluation Using a New CT Phantom." June 2012.
Source
wos-lite
Published In
Medical physics
Volume
39
Issue
6
Publish Date
2012
Start Page
4015
End Page
4015

Nuclear Medicine Uniformity Assessment Using 2D Noise Power Spectrum

Authors
Nelson, J; Christianson, O; Harkness, B; Madsen, M; Mah, E; Thomas, S; Zaidi, H; Samei, E
MLA Citation
Nelson, J, Christianson, O, Harkness, B, Madsen, M, Mah, E, Thomas, S, Zaidi, H, and Samei, E. "Nuclear Medicine Uniformity Assessment Using 2D Noise Power Spectrum." June 2012.
Source
wos-lite
Published In
Medical physics
Volume
39
Issue
6
Publish Date
2012
Start Page
3621
End Page
3621

A computerized scheme for lung nodule detection in multiprojection chest radiography.

PURPOSE: Our previous study indicated that multiprojection chest radiography could significantly improve radiologists' performance for lung nodule detection in clinical practice. In this study, the authors further verify that multiprojection chest radiography can greatly improve the performance of a computer-aided diagnostic (CAD) scheme. METHODS: Our database consisted of 59 subjects, including 43 subjects with 45 nodules and 16 subjects without nodules. The 45 nodules included 7 real and 38 simulated ones. The authors developed a conventional CAD scheme and a new fusion CAD scheme to detect lung nodules. The conventional CAD scheme consisted of four steps for (1) identification of initial nodule candidates inside lungs, (2) nodule candidate segmentation based on dynamic programming, (3) extraction of 33 features from nodule candidates, and (4) false positive reduction using a piecewise linear classifier. The conventional CAD scheme processed each of the three projection images of a subject independently and discarded the correlation information between the three images. The fusion CAD scheme included the four steps in the conventional CAD scheme and two additional steps for (5) registration of all candidates in the three images of a subject, and (6) integration of correlation information between the registered candidates in the three images. The integration step retained all candidates detected at least twice in the three images of a subject and removed those detected only once in the three images as false positives. A leave-one-subject-out testing method was used for evaluation of the performance levels of the two CAD schemes. RESULTS: At the sensitivities of 70%, 65%, and 60%, our conventional CAD scheme reported 14.7, 11.3, and 8.6 false positives per image, respectively, whereas our fusion CAD scheme reported 3.9, 1.9, and 1.2 false positives per image, and 5.5, 2.8, and 1.7 false positives per patient, respectively. The low performance of the conventional CAD scheme may be attributed to the high noise level in chest radiography, and the small size and low contrast of most nodules. CONCLUSIONS: This study indicated that the fusion of correlation information in multiprojection chest radiography can markedly improve the performance of CAD scheme for lung nodule detection.

Authors
Guo, W; Li, Q; Boyce, SJ; McAdams, HP; Shiraishi, J; Doi, K; Samei, E
MLA Citation
Guo, W, Li, Q, Boyce, SJ, McAdams, HP, Shiraishi, J, Doi, K, and Samei, E. "A computerized scheme for lung nodule detection in multiprojection chest radiography." Med Phys 39.4 (April 2012): 2001-2012.
PMID
22482621
Source
pubmed
Published In
Medical physics
Volume
39
Issue
4
Publish Date
2012
Start Page
2001
End Page
2012
DOI
10.1118/1.3694096

Quantitative CT: technique dependence of volume estimation on pulmonary nodules.

Current estimation of lung nodule size typically relies on uni- or bi-dimensional techniques. While new three-dimensional volume estimation techniques using MDCT have improved size estimation of nodules with irregular shapes, the effect of acquisition and reconstruction parameters on accuracy (bias) and precision (variance) of the new techniques has not been fully investigated. To characterize the volume estimation performance dependence on these parameters, an anthropomorphic chest phantom containing synthetic nodules was scanned and reconstructed with protocols across various acquisition and reconstruction parameters. Nodule volumes were estimated by a clinical lung analysis software package, LungVCAR. Precision and accuracy of the volume assessment were calculated across the nodules and compared between protocols via a generalized estimating equation analysis. Results showed that the precision and accuracy of nodule volume quantifications were dependent on slice thickness, with different dependences for different nodule characteristics. Other parameters including kVp, pitch, and reconstruction kernel had lower impact. Determining these technique dependences enables better volume quantification via protocol optimization and highlights the importance of consistent imaging parameters in sequential examinations.

Authors
Chen, B; Barnhart, H; Richard, S; Colsher, J; Amurao, M; Samei, E
MLA Citation
Chen, B, Barnhart, H, Richard, S, Colsher, J, Amurao, M, and Samei, E. "Quantitative CT: technique dependence of volume estimation on pulmonary nodules." Phys Med Biol 57.5 (March 7, 2012): 1335-1348.
PMID
22349265
Source
pubmed
Published In
Physics in Medicine and Biology
Volume
57
Issue
5
Publish Date
2012
Start Page
1335
End Page
1348
DOI
10.1088/0031-9155/57/5/1335

Plate-specific gain map correction for the improvement of detective quantum efficiency in computed radiography.

PURPOSE: The purpose of this work is to improve the noise power spectrum (NPS), and thus the detective quantum efficiency (DQE), of computed radiography (CR) images by correcting for spatial gain variations specific to individual imaging plates. CR devices have not traditionally employed gain-map corrections, unlike the case with flat-panel detectors, because of the multiplicity of plates used with each reader. The lack of gain-map correction has limited the DQE(f) at higher exposures with CR. This current work describes a feasible solution to generating plate-specific gain maps. METHODS: Ten high-exposure open field images were taken with an RQA5 spectrum, using a sixth generation CR plate suspended in air without a cassette. Image values were converted to exposure, the plates registered using fiducial dots on the plate, the ten images averaged, and then high-pass filtered to remove low frequency contributions from field inhomogeneity. A gain-map was then produced by converting all pixel values in the average into fractions with mean of one. The resultant gain-map of the plate was used to normalize subsequent single images to correct for spatial gain fluctuation. To validate performance, the normalized NPS (NNPS) for all images was calculated both with and without the gain-map correction. Variations in the quality of correction due to exposure levels, beam voltage/spectrum, CR reader used, and registration were investigated. RESULTS: The NNPS with plate-specific gain-map correction showed improvement over the noncorrected case over the range of frequencies from 0.15 to 2.5 mm(-1). At high exposure (40 mR), NNPS was 50%-90% better with gain-map correction than without. A small further improvement in NNPS was seen from carefully registering the gain-map with subsequent images using small fiducial dots, because of slight misregistration during scanning. Further improvement was seen in the NNPS from scaling the gain map about the mean to account for different beam spectra. CONCLUSIONS: This study demonstrates that a simple gain-map can be used to correct for the fixed-pattern noise in a given plate and thus improve the DQE of CR imaging. Such a method could easily be implemented by manufacturers because each plate has a unique bar code and the gain-map for all plates associated with a reader could be stored for future retrieval. These experiments indicated that an improvement in NPS (and hence, DQE) is possible, depending on exposure level, over a wide range of frequencies with this technique.

Authors
Schnell, EA; Samei, E; Dobbins, JT
MLA Citation
Schnell, EA, Samei, E, and Dobbins, JT. "Plate-specific gain map correction for the improvement of detective quantum efficiency in computed radiography." Med Phys 39.3 (March 2012): 1495-1504.
Website
http://hdl.handle.net/10161/2503
PMID
22380382
Source
pubmed
Published In
Medical physics
Volume
39
Issue
3
Publish Date
2012
Start Page
1495
End Page
1504
DOI
10.1118/1.3685580

Point/Counterpoint: The 2014 initiative can have potentially unintended negative consequences for medical physics in diagnostic imaging and nuclear medicine.

Authors
Samei, E; Button, TM; Orton, CG
MLA Citation
Samei, E, Button, TM, and Orton, CG. "Point/Counterpoint: The 2014 initiative can have potentially unintended negative consequences for medical physics in diagnostic imaging and nuclear medicine." Med Phys 39.3 (March 2012): 1167-1168.
PMID
22380347
Source
pubmed
Published In
Medical physics
Volume
39
Issue
3
Publish Date
2012
Start Page
1167
End Page
1168
DOI
10.1118/1.3658741

Biplane correlation imaging: a feasibility study based on phantom and human data.

The objective of this study was to implement and evaluate the performance of a biplane correlation imaging (BCI) technique aimed to reduce the effect of anatomic noise and improve the detection of lung nodules in chest radiographs. Seventy-one low-dose posterior-anterior images were acquired from an anthropomorphic chest phantom with 0.28° angular separations over a range of ±10° along the vertical axis within an 11 s interval. Similar data were acquired from 19 human subjects with institutional review board approval and informed consent. The data were incorporated into a computer-aided detection (CAD) algorithm in which suspect lesions were identified by examining the geometrical correlation of the detected signals that remained relatively constant against variable anatomic backgrounds. The data were analyzed to determine the effect of angular separation, and the overall sensitivity and false-positives for lung nodule detection. The best performance was achieved for angular separations of the projection pairs greater than 5°. Within that range, the technique provided an order of magnitude decrease in the number of false-positive reports when compared with CAD analysis of single-view images. Overall, the technique yielded ~1.1 false-positive per patient with an average sensitivity of 75%. The results indicated that the incorporation of angular information can offer a reduction in the number of false-positives without a notable reduction in sensitivity. The findings suggest that the BCI technique has the potential for clinical implementation as a cost-effective technique to improve the detection of subtle lung nodules with lowered rate of false-positives.

Authors
Samei, E; Majdi-Nasab, N; Dobbins, JT; McAdams, HP
MLA Citation
Samei, E, Majdi-Nasab, N, Dobbins, JT, and McAdams, HP. "Biplane correlation imaging: a feasibility study based on phantom and human data." J Digit Imaging 25.1 (February 2012): 137-147.
PMID
21618054
Source
pubmed
Published In
Journal of Digital Imaging
Volume
25
Issue
1
Publish Date
2012
Start Page
137
End Page
147
DOI
10.1007/s10278-011-9392-z

Pencil beam coded aperture x-ray scatter imaging

We use coded aperture x-ray scatter imaging to interrogate scattering targets with a pencil beam. Observations from a single x-ray exposure of a flat-panel scintillation detector are used to simultaneously determine the along-beam positions and momentum transfer profiles of two crystalline powders (NaCl and Al). The system operates with a 3 cm range resolution and a momentum transfer resolution of 0.1 nm 1. These results demonstrate that a single snapshot can be used to estimate scattering properties along an x-ray beam, and serve as a foundation for volumetric imaging of scattering objects. © 2012 Optical Society of America.

Authors
MacCabe, K; Krishnamurthy, K; Chawla, A; Marks, D; Samei, E; Brady, D
MLA Citation
MacCabe, K, Krishnamurthy, K, Chawla, A, Marks, D, Samei, E, and Brady, D. "Pencil beam coded aperture x-ray scatter imaging." Optics Express 20.15 (2012): 16310-16320.
Source
scival
Published In
Optics express
Volume
20
Issue
15
Publish Date
2012
Start Page
16310
End Page
16320
DOI
10.1364/OE.20.016310

Development of a dynamic 4D anthropomorphic breast phantom for contrast-based breast imaging

Mammography is currently the most widely accepted tool for detection and diagnosis of breast cancer. However, the sensitivity of mammography is reduced in women with dense breast tissue due to tissue overlap, which may obscure lesions. Digital breast tomosynthesis with contrast enhancement reduces tissue overlap and provides additional functional information about lesions (i.e. morphology and kinetics), which in turn may improve lesion characterization. The performance of such techniques is highly dependent on the structural composition of the breast, which varies significantly across patients. Therefore, optimization of breast imaging systems should be done with respect to this patient versatility. Furthermore, imaging techniques that employ contrast require the inclusion of a temporally varying breast composition with respect to the contrast agent kinetics to enable the optimization of the system. To these ends, we have developed a dynamic 4D anthropomorphic breast phantom, which can be used for optimizing a breast imaging system by incorporating material characteristics. The presented dynamic phantom is based on two recently developed anthropomorphic breast phantoms, which can be representative of a whole population through their randomized anatomical feature generation and various compression levels. The 4D dynamic phantom is incorporated with the kinetics of contrast agent uptake in different tissues and can realistically model benign and malignant lesions. To demonstrate the utility of the proposed dynamic phantom, contrast-enhanced digital mammography and breast tomosynthesis were simulated where a ray-tracing algorithm emulated the projections, a filtered back projection algorithm was used for reconstruction, and dual-energy and temporal subtractions were performed and compared. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Authors
Kiarashi, N; Lin, Y; Segars, WP; Ghate, SV; Ikejimba, L; Chen, B; Lo, JY; Iii, JTD; Nolte, LW; Samei, E
MLA Citation
Kiarashi, N, Lin, Y, Segars, WP, Ghate, SV, Ikejimba, L, Chen, B, Lo, JY, Iii, JTD, Nolte, LW, and Samei, E. "Development of a dynamic 4D anthropomorphic breast phantom for contrast-based breast imaging." 2012.
Source
scival
Published In
Proceedings of SPIE
Volume
8313
Publish Date
2012
DOI
10.1117/12.913332

Series of 4D adult XCAT phantoms for imaging research and dosimetry

Computerized phantoms are finding an increasingly important role in medical imaging research. With the ability to simulate various imaging conditions, they offer a practical means with which to quantitatively evaluate and improve imaging devices and techniques. This is especially true in CT due to the high radiation levels involved with it. Despite their utility, due to the time required to develop them, only a handful of computational models currently exist of varying detail. Most phantoms available are limited to 3D and not capable of modeling patient motion. We have previously developed a technique to rapidly create highly detailed 4D extended cardiac-torso (XCAT) phantoms based on patient CT data [1]. In this study, we utilize this technique to generate 58 new adult XCAT phantoms to be added to our growing library of virtual patients available for imaging research. These computerized patients provide a valuable tool for investigating imaging devices and the effects of anatomy and motion in imaging. They also provide the essential tools to investigate patient-specific dose estimation and optimization for adults undergoing CT procedures. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Authors
Bond, J; Frush, J; Hon, S; Eckersley, C; Williams, CH; Feng, J; Tward, DJ; Ratnanather, TJT; Miller, MI; Frush, D; Samei, E; Segars, WP
MLA Citation
Bond, J, Frush, J, Hon, S, Eckersley, C, Williams, CH, Feng, J, Tward, DJ, Ratnanather, TJT, Miller, MI, Frush, D, Samei, E, and Segars, WP. "Series of 4D adult XCAT phantoms for imaging research and dosimetry." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 8313 (2012).
Source
scival
Published In
Proceedings of SPIE
Volume
8313
Publish Date
2012
DOI
10.1117/12.911676

Patient- and cohort-specific dose and risk estimation for abdominopelvic CT: A study based on 100 patients

The purpose of this work was twofold: (a) to estimate patient- and cohort-specific radiation dose and cancer risk index for abdominopelvic computer tomography (CT) scans; (b) to evaluate the effects of patient anatomical characteristics (size, age, and gender) and CT scanner model on dose and risk conversion coefficients. The study included 100 patient models (42 pediatric models, 58 adult models) and multi-detector array CT scanners from two commercial manufacturers (LightSpeed VCT, GE Healthcare; SOMATOM Definition Flash, Siemens Healthcare). A previously-validated Monte Carlo program was used to simulate organ dose for each patient model and each scanner, from which DLP-normalized-effective dose (k factor) and DLP-normalized-risk index values (q factor) were derived. The k factor showed exponential decrease with increasing patient size. For a given gender, q factor showed exponential decrease with both increasing patient size and patient age. The discrepancies in k and q factors across scanners were on average 8% and 15%, respectively. This study demonstrates the feasibility of estimating patient-specific organ dose and cohort-specific effective dose and risk index in abdominopelvic CT requiring only the knowledge of patient size, gender, and age. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Authors
Tian, X; Li, X; Segars, WP; Frush, DP; Samei, E
MLA Citation
Tian, X, Li, X, Segars, WP, Frush, DP, and Samei, E. "Patient- and cohort-specific dose and risk estimation for abdominopelvic CT: A study based on 100 patients." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 8313 (2012).
Source
scival
Published In
Proceedings of SPIE
Volume
8313
Publish Date
2012
DOI
10.1117/12.913341

Application of a dynamic 4D anthropomorphic breast phantom in contrast-based imaging system optimization: Dual-energy or temporal subtraction?

We previously developed a dynamic 4D anthropomorphic breast phantom, which can be used to optimize contrast-based breast imaging systems, accounting for patient variability and contrast kinetics [1]. In this study we aim to compare the performance of contrast-enhanced mammographic and tomosynthesis imaging protocols followed by temporal subtraction and dual-energy subtraction, qualitatively and quantitatively across a couple of patient models. Signal-difference-to-noise ratio (SDNR) is measured for the six paradigms of contrast enhanced, temporally subtracted, and dual-energy subtracted mammography and tomosynthesis and compared. The results show how the performance is more dependent on the breast model in mammography than in tomosynthesis. Also, it is observed that dual-energy subtraction can be beneficial in mammography, whereas it is not advantageous in tomosynthesis. Lastly, the results suggest that temporal subtraction in general outperforms dual-energy subtraction. © 2012 Springer-Verlag Berlin Heidelberg.

Authors
Kiarashi, N; Ghate, SV; Lo, JY; Nolte, LW; Samei, E
MLA Citation
Kiarashi, N, Ghate, SV, Lo, JY, Nolte, LW, and Samei, E. "Application of a dynamic 4D anthropomorphic breast phantom in contrast-based imaging system optimization: Dual-energy or temporal subtraction?." Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) 7361 LNCS (2012): 658-665.
Source
scival
Published In
Lecture notes in computer science
Volume
7361 LNCS
Publish Date
2012
Start Page
658
End Page
665
DOI
10.1007/978-3-642-31271-7_85

Task-based strategy for optimized contrast enhanced breast imaging: Analysis of six imaging techniques for mammography and tomosynthesis

Digital breast tomosynthesis (DBT) is a novel x-ray imaging technique that provides 3D structural information of the breast. In contrast to 2D mammography, DBT minimizes tissue overlap potentially improving cancer detection and reducing number of unnecessary recalls. The addition of a contrast agent to DBT and mammography for lesion enhancement has the benefit of providing functional information of a lesion, as lesion contrast uptake and washout patterns may help differentiate between benign and malignant tumors. This study used a task-based method to determine the optimal imaging approach by analyzing six imaging paradigms in terms of their ability to resolve iodine at a given dose: contrast enhanced mammography and tomosynthesis, temporal subtraction mammography and tomosynthesis, and dual energy subtraction mammography and tomosynthesis. Imaging performance was characterized using a detectability index d', derived from the system task transfer function (TTF), an imaging task, iodine contrast, and the noise power spectrum (NPS). The task modeled a 5 mm lesion containing iodine concentrations between 2.1 mg/cc and 8.6 mg/cc. TTF was obtained using an edge phantom, and the NPS was measured over several exposure levels, energies, and target-filter combinations. Using a structured CIRS phantom, d' was generated as a function of dose and iodine concentration. In general, higher dose gave higher d', but for the lowest iodine concentration and lowest dose, dual energy subtraction tomosynthesis and temporal subtraction tomosynthesis demonstrated the highest performance. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Authors
Ikejimba, L; Kiarashi, N; Lin, Y; Chen, B; Ghate, SV; Zerhouni, M; Samei, E; Lo, JY
MLA Citation
Ikejimba, L, Kiarashi, N, Lin, Y, Chen, B, Ghate, SV, Zerhouni, M, Samei, E, and Lo, JY. "Task-based strategy for optimized contrast enhanced breast imaging: Analysis of six imaging techniques for mammography and tomosynthesis." 2012.
PMID
24877819
Source
scival
Published In
Proceedings of SPIE
Volume
8313
Publish Date
2012
DOI
10.1117/12.913377

3D biopsy for tomosynthesis: Simulation of prior information based reconstruction for dose and artifact reduction

Accurately targeting of small lesions for success is crucial in breast biopsy. In this paper, we proposed a new 3D tomobased biopsy, which is characterized in being more accurate, easier to perform, lower in dose, and free of metal artifact. In the scout phase, a conventional tomosynthesis scan is performed, and the reconstructed 3D image is then used for radiologists to accurately localize target volume and determine optimized needle path. In the prefire phase, two prefire stereotactic images are obtained at +24° and -24° angular levels for retrieving needle and shifted lesion locations. By combining the reconstructed 3D tomosynthesis image, needle location and lesion location, synthetic prefire and postfire images are generated for radiologists' reference before firing the real needle. The proposed scheme not only improves the biopsy accuracy but also reduces dose by 3.7-5.6 times compared to conventional mammo-based stereotactic biopsy. A simulation using anthropomorphic phantom was conducted to verify our method. Both needle and lesion were precisely recovered just based on two tomo angled images. For the needle registration, the sum of translation discrepancy is less than 3 pixels, and the sum of rotation discrepancy is less than 3 degrees. For the lesion registration, the sum of coordinate discrepancy is less than 4 pixels. The predicted 3D prefire and postfire images exhibited more intuitive spatial relationship of the shifted lesion and biopsy needle tip than mammo-based stereotactic biopsy. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Authors
Lin, Y; Ghate, S; Lo, J; Samei, E
MLA Citation
Lin, Y, Ghate, S, Lo, J, and Samei, E. "3D biopsy for tomosynthesis: Simulation of prior information based reconstruction for dose and artifact reduction." 2012.
Source
scival
Published In
Proceedings of SPIE
Volume
8313
Publish Date
2012
DOI
10.1117/12.912346

Relevance of MTF and NPS in quantitative CT: Towards developing a predictable model of quantitative performance

The quantification of lung nodule volume based on CT images provides valuable information for disease diagnosis and staging. However, the precision of the quantification is protocol, system, and technique dependent and needs to be evaluated for each specific case. To efficiently investigate the quantitative precision and find an optimal operating point, it is important to develop a predictive model based on basic system parameters. In this study, a Fourier-based metric, the estimability index (e') was proposed as such a predictor, and validated across a variety of imaging conditions. To first obtain the ground truth of quantitative precision, an anthropomorphic chest phantom with synthetic spherical nodules were imaged on a 64 slice CT scanner across a range of protocols (five exposure levels and two reconstruction algorithms). The volumes of nodules were quantified from the images using clinical software, with the precision of the quantification calculated for each protocol. To predict the precision, e' was calculated for each protocol based on several Fourier-based figures of merit, which modeled the characteristic of the quantitation task and the imaging condition (resolution, noise, etc.) of a particular protocol. Results showed a strong correlation (R 2=0.92) between the measured and predicted precision across all protocols, indicating e' as an effective predictor of the quantitative precision. This study provides a useful framework for quantification-oriented optimization of CT protocols. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Authors
Chen, B; Richard, S; Samei, E
MLA Citation
Chen, B, Richard, S, and Samei, E. "Relevance of MTF and NPS in quantitative CT: Towards developing a predictable model of quantitative performance." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 8313 (2012).
Source
scival
Published In
Proceedings of SPIE
Volume
8313
Publish Date
2012
DOI
10.1117/12.913219

CT performance as a variable function of resolution, noise, and task property for iterative reconstructions

The increasing availability of iterative reconstruction (IR) algorithms on clinical scanners is creating a demand for effectively and efficiently evaluating imaging performance and potential dose reduction. In this study, the location- and task-specific evaluation was performed using detectability index (d') by combining a task function, the task transfer function (TTF), and the noise power spectrum (NPS). Task function modeled a wide variety detection tasks in terms of shape and contrast. The TTF and NPS were measured from a physical phantom as a function of contrast and dose levels. Measured d' values were compared between three IRs (IRIS, SAFIRE3 and SAFIRE5) and conventional filtered back-projection (FBP) at various dose levels, showing an equivalent performance of IR at lower dose levels. AUC further calculated from d' showed that compared to FBP, SAFIRE5 may reduce dose by up to 50-60%; SAFIRE3 and IRIS by up to 20-30%. This study provides an initial framework for the localized and task-specific evaluation of IRs in CT and a guideline for the identification of optimal operating dose point with iterative reconstructions. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Authors
Chen, B; Richard, S; Christianson, O; Zhou, X; Samei, E
MLA Citation
Chen, B, Richard, S, Christianson, O, Zhou, X, and Samei, E. "CT performance as a variable function of resolution, noise, and task property for iterative reconstructions." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 8313 (2012).
Source
scival
Published In
Proceedings of SPIE
Volume
8313
Publish Date
2012
DOI
10.1117/12.913220

Computerized Scheme for Lung Nodule Detection in Multi-Projection Chest Radiography

Authors
Guo, W; Li, Q; Boyce, SJ; McAdams, HP; Shiraishi, J; Doi, K; Samei, E
MLA Citation
Guo, W, Li, Q, Boyce, SJ, McAdams, HP, Shiraishi, J, Doi, K, and Samei, E. "Computerized Scheme for Lung Nodule Detection in Multi-Projection Chest Radiography." 2012.
Source
wos-lite
Published In
Proceedings of SPIE - The International Society for Optical Engineering
Volume
8315
Publish Date
2012
DOI
10.1117/12.911881

The tenuous state of clinical medical physics in diagnostic imaging.

Authors
Samei, E; Anthony Seibert, J
MLA Citation
Samei, E, and Anthony Seibert, J. "The tenuous state of clinical medical physics in diagnostic imaging." Med Phys 38.12 (December 2011): iii-iv.
PMID
22149863
Source
pubmed
Published In
Medical physics
Volume
38
Issue
12
Publish Date
2011
Start Page
iii
End Page
iv
DOI
10.1118/1.3664002

Effect of gadolinium chelate contrast agents on diffusion weighted MR imaging of the liver, spleen, pancreas and kidney at 3 T.

PURPOSE: To retrospectively test the null hypotheses that the qualitative appearance of DWI and the signal intensity values in DWI and corresponding ADC values of the liver, spleen, pancreas and kidneys are identical before and after the administration of gadolinium. MATERIALS AND METHODS: Following IRB approval, DWI was acquired in 50 patients (25 male; mean age 54.9 years) prior to and after contrast administration, using single-shot echo planar imaging with b-values of 50 s/mm2 and 800 s/mm2 at 3 T. Binomial analysis was used to determine which image set was more significantly preferred in conveying the diffusion information. Pre- and post-gadolinium DWI and ADC values of corresponding regions of each organ were analyzed using standardized signal intensity measurements. RESULTS: Pre-contrast DWI images of the liver, spleen, and pancreas were preferred 52%, 49%, and 58%, respectively, with none of the differences being statistically significant. DWI of the kidneys was preferred on pre-contrast images in 83% (p<0.001). In the liver and spleen, contrast caused a significant increase in the post-contrast DWI signal intensity values at b=50 (p<0.02) and b=800 (p<0.05) but had no statistically significant effect on the ADC value (p>0.40). Pancreatic DWI signal intensity and ADC values pre- and post-contrast were also not significantly different (p=0.489). In the renal parenchyma, significant decrease in the values of DWI at b=50 (p<0.01) and b=800 (p<0.01) as well as ADC (p<0.02) was demonstrated following gadolinium administration. CONCLUSION: Intravenous gadolinium administration does not make a statistically significant difference in the qualitative appearance or ADC measurements of the liver, spleen, or pancreas when comparing pre-contrast to post-contrast DWI. In the kidneys, however, ADC values are significantly lower post-contrast with the pre-contrast diffusion weighted images also being qualitatively preferred.

Authors
Wang, CL; Chea, YW; Boll, DT; Samei, E; Neville, AM; Dale, BM; Merkle, EM
MLA Citation
Wang, CL, Chea, YW, Boll, DT, Samei, E, Neville, AM, Dale, BM, and Merkle, EM. "Effect of gadolinium chelate contrast agents on diffusion weighted MR imaging of the liver, spleen, pancreas and kidney at 3 T." Eur J Radiol 80.2 (November 2011): e1-e7.
PMID
20646887
Source
pubmed
Published In
European Journal of Radiology
Volume
80
Issue
2
Publish Date
2011
Start Page
e1
End Page
e7
DOI
10.1016/j.ejrad.2010.05.019

Synthetic positron emission tomography-computed tomography images for use in perceptual studies.

To better understand fundamental issues, perception studies of the fusion display would best be performed with a panel of lesions of variable location, size, intensity, and background. There are compelling reasons to use synthetic images that contain artificial lesions for perception research. A consideration of how to obtain this panel of lesions is the nucleus of the present review. This article is a conjoint effort of 3 groups that have joined together to review results from work that they and others have performed. The techniques we review include (1) substitution of lesions into a preexisting image matrix (either using actual prior patient-derived lesions or mathematically modeled artificial lesions), (2) addition of images (either in the attenuation-corrected image space or at an earlier stage before image reconstruction), and (3) simulation of the entire patient image. A judicious combination of the techniques discussed in this review may represent the most efficient pathway of simulating statistically varied but realistic appearing lesions.

Authors
D'Alessandro, B; Madsen, M; Samei, E; Li, X; Wooi-Tan, J; Berbaum, KS; Schartz, K; Caldwell, R; Zuckier, LS
MLA Citation
D'Alessandro, B, Madsen, M, Samei, E, Li, X, Wooi-Tan, J, Berbaum, KS, Schartz, K, Caldwell, R, and Zuckier, LS. "Synthetic positron emission tomography-computed tomography images for use in perceptual studies." Semin Nucl Med 41.6 (November 2011): 437-448. (Review)
PMID
21978446
Source
pubmed
Published In
Seminars in Nuclear Medicine
Volume
41
Issue
6
Publish Date
2011
Start Page
437
End Page
448
DOI
10.1053/j.semnuclmed.2011.06.007

Dual-energy contrast-enhanced breast tomosynthesis: optimization of beam quality for dose and image quality.

Dual-energy contrast-enhanced breast tomosynthesis is a promising technique to obtain three-dimensional functional information from the breast with high resolution and speed. To optimize this new method, this study searched for the beam quality that maximized image quality in terms of mass detection performance. A digital tomosynthesis system was modeled using a fast ray-tracing algorithm, which created simulated projection images by tracking photons through a voxelized anatomical breast phantom containing iodinated lesions. The single-energy images were combined into dual-energy images through a weighted log subtraction process. The weighting factor was optimized to minimize anatomical noise, while the dose distribution was chosen to minimize quantum noise. The dual-energy images were analyzed for the signal difference to noise ratio (SdNR) of iodinated masses. The fast ray-tracing explored 523 776 dual-energy combinations to identify which yields optimum mass SdNR. The ray-tracing results were verified using a Monte Carlo model for a breast tomosynthesis system with a selenium-based flat-panel detector. The projection images from our voxelized breast phantom were obtained at a constant total glandular dose. The projections were combined using weighted log subtraction and reconstructed using commercial reconstruction software. The lesion SdNR was measured in the central reconstructed slice. The SdNR performance varied markedly across the kVp and filtration space. Ray-tracing results indicated that the mass SdNR was maximized with a high-energy tungsten beam at 49 kVp with 92.5 µm of copper filtration and a low-energy tungsten beam at 49 kVp with 95 µm of tin filtration. This result was consistent with Monte Carlo findings. This mammographic technique led to a mass SdNR of 0.92 ± 0.03 in the projections and 3.68 ± 0.19 in the reconstructed slices. These values were markedly higher than those for non-optimized techniques. Our findings indicate that dual-energy breast tomosynthesis can be performed optimally at 49 kVp with alternative copper and tin filters, with reconstruction following weighted subtraction. The optimum technique provides best visibility of iodine against structured breast background in dual-energy contrast-enhanced breast tomosynthesis.

Authors
Samei, E; Saunders, RS
MLA Citation
Samei, E, and Saunders, RS. "Dual-energy contrast-enhanced breast tomosynthesis: optimization of beam quality for dose and image quality." Phys Med Biol 56.19 (October 7, 2011): 6359-6378.
PMID
21908902
Source
pubmed
Published In
Physics in Medicine and Biology
Volume
56
Issue
19
Publish Date
2011
Start Page
6359
End Page
6378
DOI
10.1088/0031-9155/56/19/013

Effective dose efficiency: an application-specific metric of quality and dose for digital radiography.

The detective quantum efficiency (DQE) and the effective DQE (eDQE) are relevant metrics of image quality for digital radiography detectors and systems, respectively. The current study further extends the eDQE methodology to technique optimization using a new metric of the effective dose efficiency (eDE), reflecting both the image quality as well as the effective dose (ED) attributes of the imaging system. Using phantoms representing pediatric, adult and large adult body habitus, image quality measurements were made at 80, 100, 120 and 140 kVp using the standard eDQE protocol and exposures. ED was computed using Monte Carlo methods. The eDE was then computed as a ratio of image quality to ED for each of the phantom/spectral conditions. The eDQE and eDE results showed the same trends across tube potential with 80 kVp yielding the highest values and 120 kVp yielding the lowest. The eDE results for the pediatric phantom were markedly lower than the results for the adult phantom at spatial frequencies lower than 1.2-1.7 mm(-1), primarily due to a correspondingly higher value of ED per entrance exposure. The relative performance for the adult and large adult phantoms was generally comparable but affected by kVps. The eDE results for the large adult configuration were lower than the eDE results for the adult phantom, across all spatial frequencies (120 and 140 kVp) and at spatial frequencies greater than 1.0 mm(-1) (80 and 100 kVp). Demonstrated for chest radiography, the eDE shows promise as an application-specific metric of imaging performance, reflective of body habitus and radiographic technique, with utility for radiography protocol assessment and optimization.

Authors
Samei, E; Ranger, NT; Dobbins, JT; Ravin, CE
MLA Citation
Samei, E, Ranger, NT, Dobbins, JT, and Ravin, CE. "Effective dose efficiency: an application-specific metric of quality and dose for digital radiography." Phys Med Biol 56.16 (August 21, 2011): 5099-5118.
PMID
21775791
Source
pubmed
Published In
Physics in Medicine and Biology
Volume
56
Issue
16
Publish Date
2011
Start Page
5099
End Page
5118
DOI
10.1088/0031-9155/56/16/002

Patient-specific radiation dose and cancer risk for pediatric chest CT.

PURPOSE: To estimate patient-specific radiation dose and cancer risk for pediatric chest computed tomography (CT) and to evaluate factors affecting dose and risk, including patient size, patient age, and scanning parameters. MATERIALS AND METHODS: The institutional review board approved this study and waived informed consent. This study was HIPAA compliant. The study included 30 patients (0-16 years old), for whom full-body computer models were recently created from clinical CT data. A validated Monte Carlo program was used to estimate organ dose from eight chest protocols, representing clinically relevant combinations of bow tie filter, collimation, pitch, and tube potential. Organ dose was used to calculate effective dose and risk index (an index of total cancer incidence risk). The dose and risk estimates before and after normalization by volume-weighted CT dose index (CTDI(vol)) or dose-length product (DLP) were correlated with patient size and age. The effect of each scanning parameter was studied. RESULTS: Organ dose normalized by tube current-time product or CTDI(vol) decreased exponentially with increasing average chest diameter. Effective dose normalized by tube current-time product or DLP decreased exponentially with increasing chest diameter. Chest diameter was a stronger predictor of dose than weight and total scan length. Risk index normalized by tube current-time product or DLP decreased exponentially with both chest diameter and age. When normalized by DLP, effective dose and risk index were independent of collimation, pitch, and tube potential (<10% variation). CONCLUSION: The correlations of dose and risk with patient size and age can be used to estimate patient-specific dose and risk. They can further guide the design and optimization of pediatric chest CT protocols. SUPPLEMENTAL MATERIAL: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101900/-/DC1.

Authors
Li, X; Samei, E; Segars, WP; Sturgeon, GM; Colsher, JG; Frush, DP
MLA Citation
Li, X, Samei, E, Segars, WP, Sturgeon, GM, Colsher, JG, and Frush, DP. "Patient-specific radiation dose and cancer risk for pediatric chest CT." Radiology 259.3 (June 2011): 862-874.
PMID
21467251
Source
pubmed
Published In
Radiology
Volume
259
Issue
3
Publish Date
2011
Start Page
862
End Page
874
DOI
10.1148/radiol.11101900

An anthropomorphic breast model for breast imaging simulation and optimization.

RATIONALE AND OBJECTIVES: Optimization studies for x-ray-based breast imaging systems using computer simulation can greatly benefit from a phantom capable of modeling varying anatomical variability across different patients. This study aimed to develop a three-dimensional phantom model with realistic and randomizable anatomical features. MATERIALS AND METHODS: A voxelized breast model was developed consisting of an outer layer of skin and subcutaneous fat, a mixture of glandular and adipose, stochastically generated ductal trees, masses, and microcalcifications. Randomized realization of the breast morphology provided a range of patient models. Compression models were included to represent the breast under various compression levels along different orientations. A Monte Carlo (MC) simulation code was adapted to simulate x-ray based imaging systems for the breast phantom. Simulated projections of the phantom at different angles were generated and reconstructed with iterative methods, simulating mammography, breast tomosynthesis, and computed tomography (CT) systems. Phantom dose maps were further generated for dosimetric evaluation. RESULTS: Region of interest comparisons of simulated and real mammograms showed strong similarities in terms of appearance and features. Noise-power spectra of simulated mammographic images demonstrated that the phantom provided target properties for anatomical backgrounds. Reconstructed tomosynthesis and CT images and dose maps provided corresponding data from a single breast enabling optimization studies. Dosimetry result provided insight into the dose distribution difference between modalities and compression levels. CONCLUSION: The anthropomorphic breast phantom, combined with the MC simulation platform, generated a realistic model for a breast imaging system. The developed platform is expected to provide a versatile and powerful framework for optimizing volumetric breast imaging systems.

Authors
Chen, B; Shorey, J; Saunders, RS; Richard, S; Thompson, J; Nolte, LW; Samei, E
MLA Citation
Chen, B, Shorey, J, Saunders, RS, Richard, S, Thompson, J, Nolte, LW, and Samei, E. "An anthropomorphic breast model for breast imaging simulation and optimization." Acad Radiol 18.5 (May 2011): 536-546.
PMID
21397528
Source
pubmed
Published In
Academic Radiology
Volume
18
Issue
5
Publish Date
2011
Start Page
536
End Page
546
DOI
10.1016/j.acra.2010.11.009

Lung nodule detection in pediatric chest CT: quantitative relationship between image quality and radiologist performance.

PURPOSE: To determine the quantitative relationship between image quality and radiologist performance in detecting small lung nodules in pediatric CT. METHODS: The study included clinical chest CT images of 30 pediatric patients (0-16 years) scanned at tube currents of 55-180 mA. Calibrated noise addition software was used to simulate cases at three nominal mA settings: 70, 35, and 17.5 mA, resulting in quantum noise of 7-32 Hounsfield Unit (HU). Using a validated nodule simulation technique, lung nodules with diameters of 3-5 mm and peak contrasts of 200-500 HU were inserted into the cases, which were then randomized and rated independently by four experienced pediatric radiologists for nodule presence on a continuous scale from 0 (definitely absent) to 100 (definitely present). The receiver operating characteristic (ROC) data were analyzed to quantify the relationship between diagnostic accuracy (area under the ROC curve, AUC) and image quality (the product of nodule peak contrast and displayed diameter to noise ratio, CDNR display). RESULTS: AUC increased rapidly from 0.70 to 0.87 when CDNR display increased from 60 to 130 mm, followed by a slow increase to 0.94 when CDNR display further increased to 257 mm. For the average nodule diameter (4 mm) and contrast (350 HU), AUC decreased from 0.93 to 0.71 with noise increased from 7 to 28 HU. CONCLUSIONS: We quantified the relationship between image quality and the performance of radiologists in detecting lung nodules in pediatric CT. The relationship can guide CT protocol design to achieve the desired diagnostic performance at the lowest radiation dose.]

Authors
Li, X; Samei, E; Barnhart, HX; Gaca, AM; Hollingsworth, CL; Maxfield, CM; Carrico, CWT; Colsher, JG; Frush, DP
MLA Citation
Li, X, Samei, E, Barnhart, HX, Gaca, AM, Hollingsworth, CL, Maxfield, CM, Carrico, CWT, Colsher, JG, and Frush, DP. "Lung nodule detection in pediatric chest CT: quantitative relationship between image quality and radiologist performance." Med Phys 38.5 (May 2011): 2609-2618.
PMID
21776798
Source
pubmed
Published In
Medical physics
Volume
38
Issue
5
Publish Date
2011
Start Page
2609
End Page
2618
DOI
10.1118/1.3582975

Comparative performance of multiview stereoscopic and mammographic display modalities for breast lesion detection.

PURPOSE: Mammography is known to be one of the most difficult radiographic exams to interpret. Mammography has important limitations, including the superposition of normal tissue that can obscure a mass, chance alignment of normal tissue to mimic a true lesion and the inability to derive volumetric information. It has been shown that stereomammography can overcome these deficiencies by showing that layers of normal tissue lay at different depths. If standard stereomammography (i.e., a single stereoscopic pair consisting of two projection images) can significantly improve lesion detection, how will multiview stereoscopy (MVS), where many projection images are used, compare to mammography? The aim of this study was to assess the relative performance of MVS compared to mammography for breast mass detection. METHODS: The MVS image sets consisted of the 25 raw projection images acquired over an arc of approximately 45 degrees using a Siemens prototype breast tomosynthesis system. The mammograms were acquired using a commercial Siemens FFDM system. The raw data were taken from both of these systems for 27 cases and realistic simulated mass lesions were added to duplicates of the 27 images at the same local contrast. The images with lesions (27 mammography and 27 MVS) and the images without lesions (27 mammography and 27 MVS) were then postprocessed to provide comparable and representative image appearance across the two modalities. All 108 image sets were shown to five full-time breast imaging radiologists in random order on a state-of-the-art stereoscopic display. The observers were asked to give a confidence rating for each image (0 for lesion definitely not present, 100 for lesion definitely present). The ratings were then compiled and processed using ROC and variance analysis. RESULTS: The mean AUC for the five observers was 0.614 +/- 0.055 for mammography and 0.778 +/- 0.052 for multiview stereoscopy. The difference of 0.164 +/- 0.065 was statistically significant with a p-value of 0.0148. CONCLUSIONS: The differences in the AUCs and the p-value suggest that multiview stereoscopy has a statistically significant advantage over mammography in the detection of simulated breast masses. This highlights the dominance of anatomical noise compared to quantum noise for breast mass detection. It also shows that significant lesion detection can be achieved with MVS without any of the artifacts associated with tomosynthesis.

Authors
Webb, LJ; Samei, E; Lo, JY; Baker, JA; Ghate, SV; Kim, C; Soo, MS; Walsh, R
MLA Citation
Webb, LJ, Samei, E, Lo, JY, Baker, JA, Ghate, SV, Kim, C, Soo, MS, and Walsh, R. "Comparative performance of multiview stereoscopic and mammographic display modalities for breast lesion detection." Med Phys 38.4 (April 2011): 1972-1980.
Website
http://hdl.handle.net/10161/2508
PMID
21626930
Source
pubmed
Published In
Medical physics
Volume
38
Issue
4
Publish Date
2011
Start Page
1972
End Page
1980
DOI
10.1118/1.3562901

Computed tomography dose index and dose length product for cone-beam CT: Monte Carlo simulations.

Dosimetry in kilovoltage cone beam computed tomography (CBCT) is a challenge due to the limitation of physical measurements. To address this, we used a Monte Carlo (MC) method to estimate the CT dose index (CTDI) and the dose length product (DLP) for a commercial CBCT system. As Dixon and Boone showed that CTDI concept can be applicable to both CBCT and conventional CT, we evaluated weighted CT dose index (CTDI(w)) and DLP for a commercial CBCT system. Two extended CT phantoms were created in our BEAMnrc/EGSnrc MC system. Before the simulations, the beam collimation of a Varian On-Board Imager (OBI) system was measured with radiochromic films (model: XR-QA). The MC model of the OBI X-ray tube, validated in a previous study, was used to acquire the phase space files of the full-fan and half-fan cone beams. Then, DOSXYZnrc user code simulated a total of 20 CBCT scans for the nominal beam widths from 1 cm to 10 cm. After the simulations, CBCT dose profiles at center and peripheral locations were extracted and integrated (dose profile integral, DPI) to calculate the CTDI per each beam width. The weighted cone-beam CTDI (CTDI(w,l)) was calculated from DPI values and mean CTDI(w,l) (CTDI(w,l)) and DLP were derived. We also evaluated the differences of CTDI(w) values between MC simulations and point dose measurements using standard CT phantoms. In results, it was found that CTDI(w,600) was 8.74 ± 0.01 cGy for head and CTDI(w,900) was 4.26 ± 0.01 cGy for body scan. The DLP was found to be proportional to the beam collimation. We also found that the point dose measurements with standard CT phantoms can estimate the CTDI within 3% difference compared to the full integrated CTDI from the MC method. This study showed the usability of CTDI as a dose index and DLP as a total dose descriptor in CBCT scans.

Authors
Kim, S; Song, H; Samei, E; Yin, F-F; Yoshizumi, TT
MLA Citation
Kim, S, Song, H, Samei, E, Yin, F-F, and Yoshizumi, TT. "Computed tomography dose index and dose length product for cone-beam CT: Monte Carlo simulations. (Published online)" J Appl Clin Med Phys 12.2 (January 19, 2011): 3395-.
PMID
21587186
Source
pubmed
Published In
Journal of applied clinical medical physics / American College of Medical Physics
Volume
12
Issue
2
Publish Date
2011
Start Page
3395

Patient-specific radiation dose and cancer risk estimation in CT: part II. Application to patients.

PURPOSE: Current methods for estimating and reporting radiation dose from CT examinations are largely patient-generic; the body size and hence dose variation from patient to patient is not reflected. Furthermore, the current protocol designs rely on dose as a surrogate for the risk of cancer incidence, neglecting the strong dependence of risk on age and gender. The purpose of this study was to develop a method for estimating patient-specific radiation dose and cancer risk from CT examinations. METHODS: The study included two patients (a 5-week-old female patient and a 12-year-old male patient), who underwent 64-slice CT examinations (LightSpeed VCT, GE Healthcare) of the chest, abdomen, and pelvis at our institution in 2006. For each patient, a nonuniform rational B-spine (NURBS) based full-body computer model was created based on the patient's clinical CT data. Large organs and structures inside the image volume were individually segmented and modeled. Other organs were created by transforming an existing adult male or female full-body computer model (developed from visible human data) to match the framework defined by the segmented organs, referencing the organ volume and anthropometry data in ICRP Publication 89. A Monte Carlo program previously developed and validated for dose simulation on the LightSpeed VCT scanner was used to estimate patient-specific organ dose, from which effective dose and risks of cancer incidence were derived. Patient-specific organ dose and effective dose were compared with patient-generic CT dose quantities in current clinical use: the volume-weighted CT dose index (CTDIvol) and the effective dose derived from the dose-length product (DLP). RESULTS: The effective dose for the CT examination of the newborn patient (5.7 mSv) was higher but comparable to that for the CT examination of the teenager patient (4.9 mSv) due to the size-based clinical CT protocols at our institution, which employ lower scan techniques for smaller patients. However, the overall risk of cancer incidence attributable to the CT examination was much higher for the newborn (2.4 in 1000) than for the teenager (0.7 in 1000). For the two pediatric-aged patients in our study, CTDIvol underestimated dose to large organs in the scan coverage by 30%-48%. The effective dose derived from DLP using published conversion coefficients differed from that calculated using patient-specific organ dose values by -57% to 13%, when the tissue weighting factors of ICRP 60 were used, and by -63% to 28%, when the tissue weighting factors of ICRP 103 were used. CONCLUSIONS: It is possible to estimate patient-specific radiation dose and cancer risk from CT examinations by combining a validated Monte Carlo program with patient-specific anatomical models that are derived from the patients' clinical CT data and supplemented by transformed models of reference adults. With the construction of a large library of patient-specific computer models encompassing patients of all ages and weight percentiles, dose and risk can be estimated for any patient prior to or after a CT examination. Such information may aid in decisions for image utilization and can further guide the design and optimization of CT technologies and scan protocols.

Authors
Li, X; Samei, E; Segars, WP; Sturgeon, GM; Colsher, JG; Toncheva, G; Yoshizumi, TT; Frush, DP
MLA Citation
Li, X, Samei, E, Segars, WP, Sturgeon, GM, Colsher, JG, Toncheva, G, Yoshizumi, TT, and Frush, DP. "Patient-specific radiation dose and cancer risk estimation in CT: part II. Application to patients." Med Phys 38.1 (January 2011): 408-419.
PMID
21361209
Source
pubmed
Published In
Medical physics
Volume
38
Issue
1
Publish Date
2011
Start Page
408
End Page
419
DOI
10.1118/1.3515864

Patient-specific radiation dose and cancer risk estimation in CT: part I. development and validation of a Monte Carlo program.

PURPOSE: Radiation-dose awareness and optimization in CT can greatly benefit from a dose-reporting system that provides dose and risk estimates specific to each patient and each CT examination. As the first step toward patient-specific dose and risk estimation, this article aimed to develop a method for accurately assessing radiation dose from CT examinations. METHODS: A Monte Carlo program was developed to model a CT system (LightSpeed VCT, GE Healthcare). The geometry of the system, the energy spectra of the x-ray source, the three-dimensional geometry of the bowtie filters, and the trajectories of source motions during axial and helical scans were explicitly modeled. To validate the accuracy of the program, a cylindrical phantom was built to enable dose measurements at seven different radial distances from its central axis. Simulated radial dose distributions in the cylindrical phantom were validated against ion chamber measurements for single axial scans at all combinations of tube potential and bowtie filter settings. The accuracy of the program was further validated using two anthropomorphic phantoms (a pediatric one-year-old phantom and an adult female phantom). Computer models of the two phantoms were created based on their CT data and were voxelized for input into the Monte Carlo program. Simulated dose at various organ locations was compared against measurements made with thermoluminescent dosimetry chips for both single axial and helical scans. RESULTS: For the cylindrical phantom, simulations differed from measurements by -4.8% to 2.2%. For the two anthropomorphic phantoms, the discrepancies between simulations and measurements ranged between (-8.1%, 8.1%) and (-17.2%, 13.0%) for the single axial scans and the helical scans, respectively. CONCLUSIONS: The authors developed an accurate Monte Carlo program for assessing radiation dose from CT examinations. When combined with computer models of actual patients, the program can provide accurate dose estimates for specific patients.

Authors
Li, X; Samei, E; Segars, WP; Sturgeon, GM; Colsher, JG; Toncheva, G; Yoshizumi, TT; Frush, DP
MLA Citation
Li, X, Samei, E, Segars, WP, Sturgeon, GM, Colsher, JG, Toncheva, G, Yoshizumi, TT, and Frush, DP. "Patient-specific radiation dose and cancer risk estimation in CT: part I. development and validation of a Monte Carlo program." Med Phys 38.1 (January 2011): 397-407.
PMID
21361208
Source
pubmed
Published In
Medical physics
Volume
38
Issue
1
Publish Date
2011
Start Page
397
End Page
407
DOI
10.1118/1.3515839

Precision of iodine quantification in hepatic CT: Effects of reconstruction (FBP and MBIR) and imaging parameters

In hepatic CT imaging, the lesion enhancement after the injection of contrast media is of quantitative interest. However, the precision of this quantitative measurement may be dependent on the imaging techniques such as dose and reconstruction algorithm. To determine the impact of different techniques, we scanned an iodinated liver phantom with acquisition protocols of different dose levels, and reconstructed images with different algorithms (FBP and MBIR) and slice thicknesses. The contrast of lesions was quantified from the images, and its precision was calculated for each protocol separately. Results showed that precision was improved by increasing dose, increasing slice thickness, and using MBIR reconstruction. When using MBIR instead of FBP, the same precision can be achieved at 50% less dose. To our knowledge, this is the first investigation of the quantification precision in hepatic CT imaging using iterative reconstructions. © 2011 SPIE.

Authors
Chen, B; Samei, E; Colsher, J; Barnhart, H; Marin, D; Nelson, R
MLA Citation
Chen, B, Samei, E, Colsher, J, Barnhart, H, Marin, D, and Nelson, R. "Precision of iodine quantification in hepatic CT: Effects of reconstruction (FBP and MBIR) and imaging parameters." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 7961 (2011).
Source
scival
Published In
Proceedings of SPIE
Volume
7961
Publish Date
2011
DOI
10.1117/12.878833

A patient image-based technique to assess the image quality of clinical chest radiographs

Current clinical image quality assessment techniques mainly analyze image quality for the imaging system in terms of factors such as the capture system DQE and MTF, the exposure technique, and the particular image processing method and processing parameters. However, when assessing a clinical image, radiologists seldom refer to these factors, but rather examine several specific regions of the image to see whether the image is suitable for diagnosis. In this work, we developed a new strategy to learn and simulate radiologists' evaluation process on actual clinical chest images. Based on this strategy, a preliminary study was conducted on 254 digital chest radiographs (38 AP without grids, 35 AP with 6:1 ratio grids and 151 PA with 10:1 ratio grids). First, ten regional based perceptual qualities were summarized through an observer study. Each quality was characterized in terms of a physical quantity measured from the image, and as a first step, the three physical quantities in lung region were then implemented algorithmically. A pilot observer study was performed to verify the correlation between image perceptual qualities and physical quantitative qualities. The results demonstrated that our regional based metrics have promising performance for grading perceptual properties of chest radiographs. © 2011 SPIE.

Authors
Lin, Y; Samei, E; Luo, H; Iii, JTD; McAdams, HP; Wang, X; Sehnert, WJ; Barski, L; Foos, DH
MLA Citation
Lin, Y, Samei, E, Luo, H, Iii, JTD, McAdams, HP, Wang, X, Sehnert, WJ, Barski, L, and Foos, DH. "A patient image-based technique to assess the image quality of clinical chest radiographs." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 7961 (2011).
Source
scival
Published In
Proceedings of SPIE
Volume
7961
Publish Date
2011
DOI
10.1117/12.878765

The feasibility of universal DLP-to-risk conversion coefficients for body CT protocols

The effective dose associated with computed tomography (CT) examinations is often estimated from dose-length product (DLP) using scanner-independent conversion coefficients. Such conversion coefficients are available for a small number of examinations, each covering an entire region of the body (e.g., head, neck, chest, abdomen and/or pelvis). Similar conversion coefficients, however, do not exist for examinations that cover a single organ or a sub-region of the body, as in the case of a multi-phase liver examination. In this study, we extended the DLP-to-effective dose conversion coefficient (k factor) to a wide range of body CT protocols and derived the corresponding DLP-to-cancer risk conversion coefficient (q factor). An extended cardiactorso (XCAT) computational model was used, which represented a reference adult male patient. A range of body CT protocols used in clinical practice were categorized based on anatomical regions examined into 10 protocol classes. A validated Monte Carlo program was used to estimate the organ dose associated with each protocol class. Assuming the reference model to be 20 years old, effective dose and risk index (an index of the total risk for cancer incidence) were then calculated and normalized by DLP to obtain the k and q factors. The k and q factors varied across protocol classes; the coefficients of variation were 28% and 9%, respectively. The small variation exhibited by the q factor suggested the feasibility of universal q factors for a wide range of body CT protocols. © 2011 SPIE.

Authors
Li, X; Samei, E; Segars, WP; Paulson, EK; Frush, DP
MLA Citation
Li, X, Samei, E, Segars, WP, Paulson, EK, and Frush, DP. "The feasibility of universal DLP-to-risk conversion coefficients for body CT protocols." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 7961 (2011).
Source
scival
Published In
Proceedings of SPIE
Volume
7961
Publish Date
2011
DOI
10.1117/12.878616

A new iodinated liver phantom for the quantitative evaluation of advanced CT acquisition and reconstruction techniques

An iodinated liver phantom is needed for liver CT related studies, such as the quantification of lesion contrast. Prior studies simulated iodinated hepatic lesions with tubes of iodine solution, which involved complications associated with the setup, differences from actual lesion morphology, and susceptibility to iodine sediments. To develop a dedicated liver phantom with anthropomorphic structures and solid lesions, we designed a phantom with iodinated liver inserts and lesions of different sizes and contrasts. The concentration of iodine in liver parenchyma was determined according to the HU measured from clinical images. The concentrations in high and low contrast lesions were selected so as to provide challenging but reasonable detection tasks. The application of the liver phantom was initially validated at different doses and reconstruction settings. © 2011 SPIE.

Authors
Chen, B; Marin, D; Samei, E
MLA Citation
Chen, B, Marin, D, and Samei, E. "A new iodinated liver phantom for the quantitative evaluation of advanced CT acquisition and reconstruction techniques." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 7961 (2011).
Source
scival
Published In
Proceedings of SPIE
Volume
7961
Publish Date
2011
DOI
10.1117/12.878916

Computed tomography dose index and dose length product for cone-beam CT: Monte Carlo simulations of a commercial system

Dosimetry in kilovoltage cone beam computed tomography (CBCT) is a challenge due to the limitation of physical measurements. To address this, we used a Monte Carlo (MC) method to estimate the CT dose index (CTDI) and the dose length product (DLP) for a commercial CBCT system. As Dixon and Boone(1) showed that CTDI concept can be applicable to both CBCT and conventional CT, we evaluated weighted CT dose index (CTDIw) and DLP for a commercial CBCT system. Two extended CT phantoms were created in our BEAMnrc/EGSnrc MC system. Before the simulations, the beam collimation of a Varian On-Board Imager (OBI) system was measured with radiochromic films (model: XR-QA). The MC model of the OBI X-ray tube, validated in a previous study, was used to acquire the phase space files of the full-fan and half-fan cone beams. Then, DOSXYZnrc user code simulated a total of 20 CBCT scans for the nominal beam widths from 1 cm to 10 cm. After the simulations, CBCT dose profiles at center and peripheral locations were extracted and integrated (dose profile integral, DPI) to calculate the CTDI per each beam width. The weighted cone-beam CTDI (CTDIw,l) was calculated from DPI values and mean CTDIw,l (CTDIw,l) and DLP were derived. We also evaluated the differences of CTDIw,1 values between MC simulations and point dose measurements using standard CT phantoms. In results, it was found that,CTDI600w was 8.74 ± 0.01 cGy for head and CTDI900w was 4.26 ± 0.01 cGy for body scan. The DLP was found to be proportional to the beam collimation. We also found that the point dose measurements with standard CT phantoms can estimate the CTDI within 3% difference compared to the full integrated CTDI from the MC method. This study showed the usability of CTDI as a dose index and DLP as a total dose descriptor in CBCT scans.

Authors
Kim, S; Song, H; Samei, E; Yin, F-F; Yoshizumi, TT
MLA Citation
Kim, S, Song, H, Samei, E, Yin, F-F, and Yoshizumi, TT. "Computed tomography dose index and dose length product for cone-beam CT: Monte Carlo simulations of a commercial system." Journal of Applied Clinical Medical Physics 12.2 (2011): 84-95.
Source
scival
Published In
Journal of applied clinical medical physics / American College of Medical Physics
Volume
12
Issue
2
Publish Date
2011
Start Page
84
End Page
95

3D task-based performance assessment metrics for optimization of performance and dose in breast tomosynthesis

This study aimed to investigate a method for empirically evaluating 3D imaging task performance of breast tomosynthesis imaging systems. A simulation and experimental approach was used to develop a robust method for performance assessment. To identify a method for experimentally assessing the 3D modulation transfer function (MTF), a breast tomosysnthesis system was first simulated using cascaded system analysis to model the signal and noise characteristics of the projections. A range of spheres with varying contrast and size were reconstructed using filtered back projection from which the 3D MTF was evaluated. Results revealed that smaller spheres result in lower artifacts in the measured MTF, where a sphere of 0.5 mm was found ideal for experimental purposes. A clinical tomosynthesis unit was used as a platform for quantifying the effect of acquisition and processing parameters (e.g., angular extent and sampling, dose, and voxel size) on breast imaging performance. The 3D noise-power spectrum (NPS) was measured using a uniform phantom and 3D MTF was measured using 0.5 mm ruby spheres. These metrics were combined with a mathematical description of imaging task to generate a figure of merit called the detectability index for system evaluation and optimization. Clinically relevant imaging tasks were considered, such as the detection and localization of a spherical mass. The detectability index was found to provide a useful metric that accounts for the complex 3D imaging characteristics of breast tomosynthesis. Results highlighted the dependence of optimal technique on the imaging task. They further provided initial validation of an empirically assessed figure of merit for clinical performance assessment and optimization of breast tomosynthesis systems. © 2011 SPIE.

Authors
Richard, S; Samei, E
MLA Citation
Richard, S, and Samei, E. "3D task-based performance assessment metrics for optimization of performance and dose in breast tomosynthesis." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 7961 (2011).
Source
scival
Published In
Proceedings of SPIE
Volume
7961
Publish Date
2011
DOI
10.1117/12.877070

Predictive models for observer performance in CT: Applications in protocol optimization

The relationship between theoretical descriptions of imaging performance (Fourier-based) and the performance of real human observers was investigated for detection tasks in multi-slice CT. The detectability index for the Fisher-Hotelling model observer and non-prewhitening model observer (with and without internal noise and eye filter) was computed using: 1) the measured modulation transfer function (MTF) and noise-power spectrum (NPS) for CT; and 2) a Fourier description of imaging task. Based upon CT images of human patients with added simulated lesions, human observer performance was assessed via an observer study in terms of the area under the ROC curve (Az). The degree to which the detectability index correlated with human observer performance was investigated and results for the non-prewhitening model observer with internal noise and eye filter (NPWE) were found to agree best with human performance over a broad range of imaging conditions. Results provided initial validation that CT image acquisition and reconstruction parameters can be optimized for observer performance rather than system performance (i.e., contrast-to-noise ratio, MTF, and NPS). The NPWE model was further applied for the comparison of FBP with a novel modelbased iterative reconstruction algorithm to assess its potential for dose reduction.

Authors
Richard, S; Li, X; Yadava, G; Samei, E
MLA Citation
Richard, S, Li, X, Yadava, G, and Samei, E. "Predictive models for observer performance in CT: Applications in protocol optimization." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 7961 (2011).
Source
scival
Published In
Proceedings of SPIE
Volume
7961
Publish Date
2011
DOI
10.1117/12.877069

Quantitative breast tomosynthesis: from detectability to estimability.

PURPOSE: This work aimed to extend Fourier-based imaging metrics for modeling and predicting quantitative imaging performance. The new methodology was applied to the platform of breast tomosynthesis for investigating the influence of acquisition parameters (e.g., acquisition angle and dose) on quantitative imaging performance. METHODS: Two quantitative imaging tasks were considered: Area estimation and volume estimation of a 4 mm diameter spherical target. The maximum likelihood estimator yielded training data to generate a size estimation task function, which was combined with the MTF and NPS to predict estimation performance by computing an "estimability index" analogous to the detectability index. Estimation performance for the two tasks was computed as a function of acquisition angle and dose. The results were used for system optimization in terms of quantitation performance and further compared to the detectability index for the detection of the same spherical target. RESULTS: The estimability index computed with the size estimation tasks correlated well with precision measurements for area and volume estimation over a broad range of imaging conditions and provided a meaningful figure of merit for quantitative imaging performance and optimization. The results highlighted that optimal breast tomosynthesis acquisition parameters depend significantly on imaging task and dose. At nominal dose (1.5 mGy), mass detection was optimal at an acquisition angle of 85 degrees, while area and volume estimation for the same mass were optimal at approximately 125 degrees and 164 degrees acquisition angles, respectively. CONCLUSIONS: These findings provide an initial validation that the Fourier-based metrics extended to estimation tasks can represent a meaningful metric and predictor of quantitative imaging performance. The optimization framework also revealed trade-off between anatomical noise and system noise in volumetric imaging systems potentially identifying different optimal acquisition parameters than currently used in breast tomosynthesis and CT.

Authors
Richard, S; Samei, E
MLA Citation
Richard, S, and Samei, E. "Quantitative breast tomosynthesis: from detectability to estimability." Med Phys 37.12 (December 2010): 6157-6165.
PMID
21302772
Source
pubmed
Published In
Medical physics
Volume
37
Issue
12
Publish Date
2010
Start Page
6157
End Page
6165
DOI
10.1118/1.3501883

Detection of pancreatic tumors, image quality, and radiation dose during the pancreatic parenchymal phase: effect of a low-tube-voltage, high-tube-current CT technique--preliminary results.

PURPOSE: To intraindividually compare a low-tube-voltage (80 kVp), high-tube-current (675 mA) computed tomographic (CT) technique with a high-tube-voltage (140 kVp) CT protocol for the detection of pancreatic tumors, image quality, and radiation dose during the pancreatic parenchymal phase. MATERIALS AND METHODS: This prospective, single-center, HIPAA-compliant study was approved by the institutional review board, and written informed consent was obtained. Twenty-seven patients (nine men, 18 women; mean age, 64 years) with 23 solitary pancreatic tumors underwent dual-energy CT. Two imaging protocols were used: 140 kVp and 385 mA (protocol A) and 80 kVp and 675 mA (protocol B). For both protocols, the following variables were compared during the pancreatic parenchymal phase: contrast enhancement for the aorta, the pancreas, and the portal vein; pancreas-to-tumor contrast-to-noise ratio (CNR); noise; and effective dose. Two blinded, independent readers qualitatively scored the two data sets for tumor detection and image quality. Random-effect analysis of variance tests were used to compare differences between the two protocols. RESULTS: Compared with protocol A, protocol B yielded significantly higher contrast enhancement for the aorta (508.6 HU vs 221.5 HU, respectively), pancreas (151.2 HU vs 67.0 HU), and portal vein (189.7 HU vs 87.3 HU), along with a greater pancreas-to-tumor CNR (8.1 vs 5.9) (P < .001 for all comparisons). No statistically significant difference in tumor detection was observed between the two protocols. Although standard deviation of image noise increased with protocol B (11.5 HU vs 18.6 HU), this protocol significantly reduced the effective dose (from 18.5 to 5.1 mSv; P < .001). CONCLUSION: A low-tube-voltage, high-tube-current CT technique has the potential to improve the enhancement of the pancreas and peripancreatic vasculature, improve tumor conspicuity, and reduce patient radiation dose during the pancreatic parenchymal phase.

Authors
Marin, D; Nelson, RC; Barnhart, H; Schindera, ST; Ho, LM; Jaffe, TA; Yoshizumi, TT; Youngblood, R; Samei, E
MLA Citation
Marin, D, Nelson, RC, Barnhart, H, Schindera, ST, Ho, LM, Jaffe, TA, Yoshizumi, TT, Youngblood, R, and Samei, E. "Detection of pancreatic tumors, image quality, and radiation dose during the pancreatic parenchymal phase: effect of a low-tube-voltage, high-tube-current CT technique--preliminary results." Radiology 256.2 (August 2010): 450-459.
PMID
20656835
Source
pubmed
Published In
Radiology
Volume
256
Issue
2
Publish Date
2010
Start Page
450
End Page
459
DOI
10.1148/radiol.10091819

Kilovoltage cone-beam CT: comparative dose and image quality evaluations in partial and full-angle scan protocols.

PURPOSE: To assess imaging dose of partial and full-angle kilovoltage CBCT scan protocols and to evaluate image quality for each protocol. METHODS: The authors obtained the CT dose index (CTDI) of the kilovoltage CBCT protocols in an on-board imager by ion chamber (IC) measurements and Monte Carlo (MC) simulations. A total of six new CBCT scan protocols were evaluated: Standard-dose head (100 kVp, 151 mA s, partial-angle), low-dose head (100 kVp, 75 mA s, partial-angle), high-quality head (100 kVp, 754 mA s, partial-angle), pelvis (125 kVp, 706 mA s, full-angle), pelvis spotlight (125 kVp, 752 mA s, partial-angle), and low-dose thorax (110 kVp, 271 mA s, full-angle). Using the point dose method, various CTDI values were calculated by (1) the conventional weighted CTDI (CTDIw) calculation and (2) Bakalyar's method (CTDIwb). The MC simulations were performed to obtain the CTDIw and CTDIwb, as well as from (3) central slice averaging (CTDI(2D)) and (4) volume averaging (CTDI(3D)) techniques. The CTDI values of the new protocols were compared to those of the old protocols (full-angle CBCT protocols). Image quality of the new protocols was evaluated following the CBCT image quality assurance (QA) protocol [S. Yoo et al., "A quality assurance program for the on-board image, "Med. Phys. 33(11), 4431-4447 (2006)] testing Hounsfield unit (HU) linearity, spatial linearity/resolution, contrast resolution, and HU uniformity. RESULTS: The CTDI, were found as 6.0, 3.2, 29.0, 25.4, 23.8, and 7.7 mGy for the new protocols, respectively. The CTDI, and CTDIwb differed within +3% between IC measurements and MC simulations. Method (2) results were within +/- 12% of method (1). In MC simulations, the CTDIw and CTDIwb were comparable to the CTDI(2D) and CTDI(3D) with the differences ranging from -4.3% to 20.6%. The CTDI(3D) were smallest among all the CTDI values. CTDIw of the new protocols were found as approximately 14 times lower for standard head scan and 1.8 times lower for standard body scan than the old protocols, respectively. In the image quality QA tests, all the protocols except low-dose head and low-dose thorax protocols were within the tolerance in the HU verification test. The HU value for the two protocols was always higher than the nominal value. All the protocols passed the spatial linearity/resolution and HU uniformity tests. In the contrast resolution test, only high-quality head and pelvis scan protocols were within the tolerance. In addition, crescent effect was found in the partial-angle scan protocols. CONCLUSIONS: The authors found that CTDIw of the new CBCT protocols has been significantly reduced compared to the old protocols with acceptable image quality. The CTDIw values in the point dose method were close to the volume averaging method within 9%-21% for all the CBCT scan protocols. The Bakalyar's method produced more accurate dose estimation within 14%. The HU inaccuracy from low-dose head and low-dose thorax protocols can render incorrect dose results in the treatment planning system. When high soft-tissue contrast data are desired, high-quality head or pelvis scan protocol is recommended depending on the imaging area. The point dose method can be applicable to estimate CBCT dose with reasonable accuracy in the clinical environment.

Authors
Kim, S; Yoo, S; Yin, F-F; Samei, E; Yoshizumi, T
MLA Citation
Kim, S, Yoo, S, Yin, F-F, Samei, E, and Yoshizumi, T. "Kilovoltage cone-beam CT: comparative dose and image quality evaluations in partial and full-angle scan protocols." Med Phys 37.7 (July 2010): 3648-3659.
PMID
20831072
Source
pubmed
Published In
Medical physics
Volume
37
Issue
7
Publish Date
2010
Start Page
3648
End Page
3659
DOI
10.1118/1.3438478

Quantitative imaging in breast tomosynthesis and CT: comparison of detection and estimation task performance.

PURPOSE: This work investigates a framework for modeling volumetric breast imaging to compare detection and estimation task performance and optimize quantitative breast imaging. METHODS: Volumetric reconstructions of a breast phantom, which incorporated electronic, quantum, and anatomical noise with embedded spherical lesions, were simulated over a range of acquisition angles varying from 4 degrees to 204 degrees with a constant total acquisition dose of 1.5 mGy. A maximum likelihood estimator was derived in terms of the noise power spectrum, which yielded figures of merit for quantitative imaging performance in terms of accuracy and precision. These metrics were computed for estimation of lesion area, volume, and location. Estimation task performance was optimized as a function of acquisition angle and compared to the performance of a more conventional lesion detection task. RESULTS: Results revealed tradeoffs between electronic, quantum, and anatomical noise. The detection of a 4 mm sphere was optimal at an acquisition angle of 84 degrees, where reconstructed images using a smaller acquisition angle exhibited increased anatomical noise and reconstructed images using a larger acquisition angle exhibited increased quantum and electronic noise. For all estimation tasks, accuracy was found to be fairly constant as a function acquisition angle indicating adequate system calibration, whereas a more significant dependence on acquisition angle was observed for precision performance. Precision for the 2D area estimation task was optimal at approximately 104 degrees, while precision of the 3D volume estimation task was optimal at larger angles (approximately 124 degrees). Precision for the localization task showed orientation dependence where localization was significantly inferior in the depth direction. Overall, precision for localization was optimal at larger angles (i.e., > 125 degrees) compared to the size estimation tasks. Results suggested that for quantitative imaging tasks, the acquisition angle should be larger than currently used in conventional breast tomosynthesis for lesion detection. CONCLUSIONS: Analysis of quantitative imaging performance using Fourier-based metrics highlights the difference between estimation and detection task in volumetric breast imaging and provides a meaningful framework for optimizing the performance of breast imaging systems for quantitative imaging applications.

Authors
Richard, S; Samei, E
MLA Citation
Richard, S, and Samei, E. "Quantitative imaging in breast tomosynthesis and CT: comparison of detection and estimation task performance." Med Phys 37.6 (June 2010): 2627-2637.
PMID
20632574
Source
pubmed
Published In
Medical physics
Volume
37
Issue
6
Publish Date
2010
Start Page
2627
End Page
2637
DOI
10.1118/1.3429025

The quantitative potential for breast tomosynthesis imaging.

PURPOSE: Due to its limited angular scan range, breast tomosynthesis has lower resolution in the depth direction, which may limit its accuracy in quantifying tissue density. This study assesses the quantitative potential of breast tomosynthesis using relatively simple reconstruction and image processing algorithms. This quantitation could allow improved characterization of lesions as well as image processing to present tomosynthesis images with the familiar appearance of mammography by preserving more low-frequency information. METHODS: All studies were based on a Siemens prototype MAMMOMAT Novation TOMO breast tomo system with a 45 degrees total angular span. This investigation was performed using both simulations and empirical measurements. Monte Carlo simulations were conducted using the breast tomosynthesis geometry and tissue-equivalent, uniform, voxelized phantoms with cuboid lesions of varying density embedded within. Empirical studies were then performed using tissue-equivalent plastic phantoms which were imaged on the actual prototype system. The material surrounding the lesions was set to either fat-equivalent or glandular-equivalent plastic. From the simulation experiments, the effects of scatter, lesion depth, and background material density were studied. The empirical experiments studied the effects of lesion depth, background material density, x-ray tube energy, and exposure level. Additionally, the proposed analysis methods were independently evaluated using a commercially available QA breast phantom (CIRS Model 11A). All image reconstruction was performed with a filtered backprojection algorithm. Reconstructed voxel values within each slice were corrected to reduce background nonuniformities. RESULTS: The resulting lesion voxel values varied linearly with known glandular fraction (correlation coefficient R2 > 0.90) under all simulated and empirical conditions, including for the independent tests with the QA phantom. Analysis of variance performed on the fit line parameters revealed statistically significant differences between the two different background materials and between 28 kVp and the remaining energies (26, 30, and 32 kVp) for the dense experimental phantom. How ever, no significant differences arose between different energies for the fatty phantom, nor for any of the many other combinations of parameters. CONCLUSIONS: These strong linear relationships suggest that breast tomosynthesis image voxel values, after being corrected by our outlined methods, are highly positively correlated with true tissue density. This consistent linearity implies that breast tomosynthesis imaging indeed has potential to be quantitative.

Authors
Shafer, CM; Samei, E; Lo, JY
MLA Citation
Shafer, CM, Samei, E, and Lo, JY. "The quantitative potential for breast tomosynthesis imaging." Med Phys 37.3 (March 2010): 1004-1016.
PMID
20384236
Source
pubmed
Published In
Medical physics
Volume
37
Issue
3
Publish Date
2010
Start Page
1004
End Page
1016
DOI
10.1118/1.3285038

A technique optimization protocol and the potential for dose reduction in digital mammography.

Digital mammography requires revisiting techniques that have been optimized for prior screen/film mammography systems. The objective of the study was to determine optimized radiographic technique for a digital mammography system and demonstrate the potential for dose reduction in comparison to the clinically established techniques based on screen- film. An objective figure of merit (FOM) was employed to evaluate a direct-conversion amorphous selenium (a-Se) FFDM system (Siemens Mammomat Novation(DR), Siemens AG Medical Solutions, Erlangen, Germany) and was derived from the quotient of the squared signal-difference-to-noise ratio to mean glandular dose, for various combinations of technique factors and breast phantom configurations including kilovoltage settings (23-35 kVp), target/filter combinations (Mo-Mo and W-Rh), breast-equivalent plastic in various thicknesses (2-8 cm) and densities (100% adipose, 50% adipose/50% glandular, and 100% glandular), and simulated mass and calcification lesions. When using a W-Rh spectrum, the optimized FOM results for the simulated mass and calcification lesions showed highly consistent trends with kVp for each combination of breast density and thickness. The optimized kVp ranged from 26 kVp for 2 cm 100% adipose breasts to 30 kVp for 8 cm 100% glandular breasts. The use of the optimized W-Rh technique compared to standard Mo-Mo techniques provided dose savings ranging from 9% for 2 cm thick, 100% adipose breasts, to 63% for 6 cm thick, 100% glandular breasts, and for breasts with a 50% adipose/50% glandular composition, from 12% for 2 cm thick breasts up to 57% for 8 cm thick breasts.

Authors
Ranger, NT; Lo, JY; Samei, E
MLA Citation
Ranger, NT, Lo, JY, and Samei, E. "A technique optimization protocol and the potential for dose reduction in digital mammography." Med Phys 37.3 (March 2010): 962-969.
PMID
20384232
Source
pubmed
Published In
Medical physics
Volume
37
Issue
3
Publish Date
2010
Start Page
962
End Page
969
DOI
10.1118/1.3276732

Generalized "satisfaction of search": adverse influences on dual-target search accuracy.

The successful detection of a target in a radiological search can reduce the detectability of a second target, a phenomenon termed satisfaction of search (SOS). Given the potential consequences, here we investigate the generality of SOS with the goal of simultaneously informing radiology, cognitive psychology, and nonmedical searches such as airport luggage screening. Ten experiments utilizing nonmedical searches and untrained searchers suggest that SOS is affected by a diverse array of factors, including (1) the relative frequency of different target types, (2) external pressures (reward and time), and (3) expectations about the number of targets present. Collectively, these experiments indicate that SOS arises when searchers have a biased expectation about the low likelihood of specific targets or events, and when they are under pressure to perform efficiently. This first demonstration of SOS outside of radiology implicates a general heuristic applicable to many kinds of searches. In an example like airport luggage screening, the current data suggest that the detection of an easy-to-spot target (e.g., a water bottle) might reduce detection of a hard-to-spot target (e.g., a box cutter).

Authors
Fleck, MS; Samei, E; Mitroff, SR
MLA Citation
Fleck, MS, Samei, E, and Mitroff, SR. "Generalized "satisfaction of search": adverse influences on dual-target search accuracy." J Exp Psychol Appl 16.1 (March 2010): 60-71.
PMID
20350044
Source
pubmed
Published In
Journal of Experimental Psychology: Applied
Volume
16
Issue
1
Publish Date
2010
Start Page
60
End Page
71
DOI
10.1037/a0018629

Low-tube-voltage, high-tube-current multidetector abdominal CT: improved image quality and decreased radiation dose with adaptive statistical iterative reconstruction algorithm--initial clinical experience.

PURPOSE: To investigate whether an adaptive statistical iterative reconstruction (ASIR) algorithm improves the image quality at low-tube-voltage (80-kVp), high-tube-current (675-mA) multidetector abdominal computed tomography (CT) during the late hepatic arterial phase. MATERIALS AND METHODS: This prospective, single-center HIPAA-compliant study was institutional review board approved. Informed patient consent was obtained. Ten patients (six men, four women; mean age, 63 years; age range, 51-77 years) known or suspected to have hypervascular liver tumors underwent dual-energy 64-section multidetector CT. High- and low-tube-voltage CT images were acquired sequentially during the late hepatic arterial phase of contrast enhancement. Standard convolution FBP was used to reconstruct 140-kVp (protocol A) and 80-kVp (protocol B) image sets, and ASIR (protocol C) was used to reconstruct 80-kVp image sets. The mean image noise; contrast-to-noise ratio (CNR) relative to muscle for the aorta, liver, and pancreas; and effective dose with each protocol were assessed. A figure of merit (FOM) was computed to normalize the image noise and CNR for each protocol to effective dose. Repeated-measures analysis of variance with Bonferroni adjustment for multiple comparisons was used to compare differences in mean CNR, image noise, and corresponding FOM among the three protocols. The noise power spectra generated from a custom phantom with each protocol were also compared. RESULTS: When image noise was normalized to effective dose, protocol C, as compared with protocols A (P = .0002) and B (P = .0001), yielded an approximately twofold reduction in noise. When the CNR was normalized to effective dose, protocol C yielded significantly higher CNRs for the aorta, liver, and pancreas than did protocol A (P = .0001 for all comparisons) and a significantly higher CNR for the liver than did protocol B (P = .003). Mean effective doses were 17.5 mSv +/- 0.6 (standard error) with protocol A and 5.1 mSv +/- 0.3 with protocols B and C. Compared with protocols A and B, protocol C yielded a small but quantifiable noise reduction across the entire spectrum of spatial frequencies. CONCLUSION: Compared with standard FBP reconstruction, an ASIR algorithm improves image quality and has the potential to decrease radiation dose at low-tube-voltage, high-tube-current multidetector abdominal CT during the late hepatic arterial phase.

Authors
Marin, D; Nelson, RC; Schindera, ST; Richard, S; Youngblood, RS; Yoshizumi, TT; Samei, E
MLA Citation
Marin, D, Nelson, RC, Schindera, ST, Richard, S, Youngblood, RS, Yoshizumi, TT, and Samei, E. "Low-tube-voltage, high-tube-current multidetector abdominal CT: improved image quality and decreased radiation dose with adaptive statistical iterative reconstruction algorithm--initial clinical experience." Radiology 254.1 (January 2010): 145-153.
PMID
20032149
Source
pubmed
Published In
Radiology
Volume
254
Issue
1
Publish Date
2010
Start Page
145
End Page
153
DOI
10.1148/radiol.09090094

Quantification of radiographic image quality based on patient anatomical contrast-to-noise ratio: A preliminary study with chest images

The quality of a digital radiograph for diagnostic imaging depends on many factors, such as the capture system DQE and MTF, the exposure technique factors, the patient anatomy, and the particular image processing method and processing parameters used. Therefore, the overall image quality as perceived by the radiologists depends on many factors. This work explores objective image quality metrics directly from display-ready patient images. A preliminary study was conducted based on a multi-frequency analysis of anatomy contrast and noise magnitude from 250 computed radiography (CR) chest radiographs (150 PA, 50 AP captured with anti-scatter grids, and 50 AP without grids). The contrast and noise values were evaluated in different sub-bands separately according to their frequency properties. Contrast-Noise ratio (CNR) was calculated, the results correlated well with the human observers' overall impression on the images captured with and without grids. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Authors
Lin, Y; Wang, X; Sehnert, WJ; Foos, DH; Barski, L; Samei, E
MLA Citation
Lin, Y, Wang, X, Sehnert, WJ, Foos, DH, Barski, L, and Samei, E. "Quantification of radiographic image quality based on patient anatomical contrast-to-noise ratio: A preliminary study with chest images." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 7627 (2010).
Source
scival
Published In
Proceedings of SPIE
Volume
7627
Publish Date
2010
DOI
10.1117/12.847033

Constancy checking of digital breast tomosynthesis systems

As the number of installed digital breast tomosynthesis (DBT) systems increases, the need for quality control routines rises. Current work reports on our initial experience with a newly developed method for the analysis of DBT acquisitions of a homogenous phantom. Both the uniformity of the projection as of the reconstruction data is analyzed, together with the in-plane and inter-plane noise variations. The approach was tested in 2 different ways: on DBT projection and reconstructed data of different vendors and via simulations of potential detector artifacts known from 2D mammography into the projection images of the DBT (and followed by reconstruction of the hybrid data). The following potentially disturbing artifacts were observed: localized detector artifacts, modification of reconstruction software settings and synchronization issues. Our results indicate that the proposed method could be an easy and reliable way of performing constancy checking of DBT systems. © 2010 Springer-Verlag.

Authors
Jacobs, J; Marshall, N; Cockmartin, L; Samei, E; Bosmans, H
MLA Citation
Jacobs, J, Marshall, N, Cockmartin, L, Samei, E, and Bosmans, H. "Constancy checking of digital breast tomosynthesis systems." Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) 6136 LNCS (2010): 518-525.
Source
scival
Published In
Lecture notes in computer science
Volume
6136 LNCS
Publish Date
2010
Start Page
518
End Page
525
DOI
10.1007/978-3-642-13666-5_70

Erratum: An exposure indicator for digital radiography: AAPM Task Group 116 (Executive Summary) (Medical Physics (2009) 36 (2898-2914))

Authors
Shepard, SJ; Wang, J; Flynn, M; Gingold, E; Goldman, L; Krugh, K; Leong, DL; Mah, E; Ogden, K; Peck, D; Samei, E; Willis, CE
MLA Citation
Shepard, SJ, Wang, J, Flynn, M, Gingold, E, Goldman, L, Krugh, K, Leong, DL, Mah, E, Ogden, K, Peck, D, Samei, E, and Willis, CE. "Erratum: An exposure indicator for digital radiography: AAPM Task Group 116 (Executive Summary) (Medical Physics (2009) 36 (2898-2914))." Medical Physics 37.1 (2010): 405--.
Source
scival
Published In
Medical physics
Volume
37
Issue
1
Publish Date
2010
Start Page
405-
DOI
10.1118/1.3266686

Patient-Specific Radiation Dose and Cancer Risk Estimation in Pediatric Chest CT: A Study in 30 Patients

Authors
Lia, X; Samei, E; Segars, WP; Sturgeon, GM; Colsher, JG; Frush, DP
MLA Citation
Lia, X, Samei, E, Segars, WP, Sturgeon, GM, Colsher, JG, and Frush, DP. "Patient-Specific Radiation Dose and Cancer Risk Estimation in Pediatric Chest CT: A Study in 30 Patients." 2010.
Source
wos-lite
Published In
Proceedings of SPIE - The International Society for Optical Engineering
Volume
7622
Publish Date
2010
DOI
10.1117/12.845491

Quantitative CT: Technique Dependency of Volume Assessment for Pulmonary Nodules

Authors
Chen, B; Richard, S; Barnhart, H; Colsher, J; Amurao, M; Samei, E
MLA Citation
Chen, B, Richard, S, Barnhart, H, Colsher, J, Amurao, M, and Samei, E. "Quantitative CT: Technique Dependency of Volume Assessment for Pulmonary Nodules." 2010.
Source
wos-lite
Published In
Proceedings of SPIE - The International Society for Optical Engineering
Volume
7622
Publish Date
2010
DOI
10.1117/12.845493

The myth of mean dose as a surrogate for radiation risk?

Authors
Samei, E; Li, X; Chen, B; Reiman, R
MLA Citation
Samei, E, Li, X, Chen, B, and Reiman, R. "The myth of mean dose as a surrogate for radiation risk?." 2010.
Source
wos-lite
Published In
Proceedings of SPIE - The International Society for Optical Engineering
Volume
7622
Publish Date
2010
DOI
10.1117/12.845940

Towards an international consensus strategy for periodic quality control of digital breast tomosynthesis systems

Authors
Jacobs, J; Marshall, N; Cockmartin, L; Zanca, F; van Engen, R; Young, K; Bosmans, H; Samei, E
MLA Citation
Jacobs, J, Marshall, N, Cockmartin, L, Zanca, F, van Engen, R, Young, K, Bosmans, H, and Samei, E. "Towards an international consensus strategy for periodic quality control of digital breast tomosynthesis systems." 2010.
Source
wos-lite
Published In
Proceedings of SPIE - The International Society for Optical Engineering
Volume
7622
Publish Date
2010
DOI
10.1117/12.844228

Extending the Detectability Index to Quantitative Imaging Performance: Applications in Tomosynthesis and CT

Authors
Richard, S; Chen, B; Samei, E
MLA Citation
Richard, S, Chen, B, and Samei, E. "Extending the Detectability Index to Quantitative Imaging Performance: Applications in Tomosynthesis and CT." 2010.
Source
wos-lite
Published In
Proceedings of SPIE - The International Society for Optical Engineering
Volume
7622
Publish Date
2010
DOI
10.1117/12.845286

Wide-angle Breast Tomosynthesis: Initial Comparative Evaluation

Authors
Thompson, J; Chen, B; Richard, S; Bowsher, J; Samei, E
MLA Citation
Thompson, J, Chen, B, Richard, S, Bowsher, J, and Samei, E. "Wide-angle Breast Tomosynthesis: Initial Comparative Evaluation." 2010.
Source
wos-lite
Published In
Proceedings of SPIE - The International Society for Optical Engineering
Volume
7622
Publish Date
2010
DOI
10.1117/12.845649

Optimized image acquisition for breast tomosynthesis in projection and reconstruction space.

Breast tomosynthesis has been an exciting new development in the field of breast imaging. While the diagnostic improvement via tomosynthesis is notable, the full potential of tomosynthesis has not yet been realized. This may be attributed to the dependency of the diagnostic quality of tomosynthesis on multiple variables, each of which needs to be optimized. Those include dose, number of angular projections, and the total angular span of those projections. In this study, the authors investigated the effects of these acquisition parameters on the overall diagnostic image quality of breast tomosynthesis in both the projection and reconstruction space. Five mastectomy specimens were imaged using a prototype tomosynthesis system. 25 angular projections of each specimen were acquired at 6.2 times typical single-view clinical dose level. Images at lower dose levels were then simulated using a noise modification routine. Each projection image was supplemented with 84 simulated 3 mm 3D lesions embedded at the center of 84 nonoverlapping ROIs. The projection images were then reconstructed using a filtered backprojection algorithm at different combinations of acquisition parameters to investigate which of the many possible combinations maximizes the performance. Performance was evaluated in terms of a Laguerre-Gauss channelized Hotelling observer model-based measure of lesion detectability. The analysis was also performed without reconstruction by combining the model results from projection images using Bayesian decision fusion algorithm. The effect of acquisition parameters on projection images and reconstructed slices were then compared to derive an optimization rule for tomosynthesis. The results indicated that projection images yield comparable but higher performance than reconstructed images. Both modes, however, offered similar trends: Performance improved with an increase in the total acquisition dose level and the angular span. Using a constant dose level and angular span, the performance rolled off beyond a certain number of projections, indicating that simply increasing the number of projections in tomosynthesis may not necessarily improve its performance. The best performance for both projection images and tomosynthesis slices was obtained for 15-17 projections spanning an angular are of approximately 45 degrees--the maximum tested in our study, and for an acquisition dose equal to single-view mammography. The optimization framework developed in this framework is applicable to other reconstruction techniques and other multiprojection systems.

Authors
Chawla, AS; Lo, JY; Baker, JA; Samei, E
MLA Citation
Chawla, AS, Lo, JY, Baker, JA, and Samei, E. "Optimized image acquisition for breast tomosynthesis in projection and reconstruction space." Med Phys 36.11 (November 2009): 4859-4869.
PMID
19994493
Source
pubmed
Published In
Medical physics
Volume
36
Issue
11
Publish Date
2009
Start Page
4859
End Page
4869
DOI
10.1118/1.3231814

Effective DQE (eDQE) and speed of digital radiographic systems: an experimental methodology.

Prior studies on performance evaluation of digital radiographic systems have primarily focused on the assessment of the detector performance alone. However, the clinical performance of such systems is also substantially impacted by magnification, focal spot blur, the presence of scattered radiation, and the presence of an antiscatter grid. The purpose of this study is to evaluate an experimental methodology to assess the performance of a digital radiographic system, including those attributes, and to propose a new metric, effective detective quantum efficiency (eDQE), a candidate for defining the efficiency or speed of digital radiographic imaging systems. The study employed a geometric phantom simulating the attenuation and scatter properties of the adult human thorax and a representative indirect flat-panel-based clinical digital radiographic imaging system. The noise power spectrum (NPS) was derived from images of the phantom acquired at three exposure levels spanning the operating range of the clinical system. The modulation transfer function (MTF) was measured using an edge device positioned at the surface of the phantom, facing the x-ray source. Scatter measurements were made using a beam stop technique. The eDQE was then computed from these measurements, along with measures of phantom attenuation and x-ray flux. The MTF results showed notable impact from the focal spot blur, while the NPS depicted a large component of structured noise resulting from use of an antiscatter grid. The eDQE was found to be an order of magnitude lower than the conventional DQE. At 120 kVp, eDQE(0) was in the 8%-9% range, fivefold lower than DQE(0) at the same technique. The eDQE method yielded reproducible estimates of the system performance in a clinically relevant context by quantifying the inherent speed of the system, that is, the actual signal to noise ratio that would be measured under clinical operating conditions.

Authors
Samei, E; Ranger, NT; MacKenzie, A; Honey, ID; Dobbins, JT; Ravin, CE
MLA Citation
Samei, E, Ranger, NT, MacKenzie, A, Honey, ID, Dobbins, JT, and Ravin, CE. "Effective DQE (eDQE) and speed of digital radiographic systems: an experimental methodology." Med Phys 36.8 (August 2009): 3806-3817.
PMID
19746814
Source
pubmed
Published In
Medical physics
Volume
36
Issue
8
Publish Date
2009
Start Page
3806
End Page
3817
DOI
10.1118/1.3171690

An exposure indicator for digital radiography: AAPM Task Group 116 (executive summary).

Digital radiographic imaging systems, such as those using photostimulable storage phosphor, amorphous selenium, amorphous silicon, CCD, and MOSFET technology, can produce adequate image quality over a much broader range of exposure levels than that of screen/film imaging systems. In screen/film imaging, the final image brightness and contrast are indicative of over- and underexposure. In digital imaging, brightness and contrast are often determined entirely by digital postprocessing of the acquired image data. Overexposure and underexposures are not readily recognizable. As a result, patient dose has a tendency to gradually increase over time after a department converts from screen/film-based imaging to digital radiographic imaging. The purpose of this report is to recommend a standard indicator which reflects the radiation exposure that is incident on a detector after every exposure event and that reflects the noise levels present in the image data. The intent is to facilitate the production of consistent, high quality digital radiographic images at acceptable patient doses. This should be based not on image optical density or brightness but on feedback regarding the detector exposure provided and actively monitored by the imaging system. A standard beam calibration condition is recommended that is based on RQA5 but uses filtration materials that are commonly available and simple to use. Recommendations on clinical implementation of the indices to control image quality and patient dose are derived from historical tolerance limits and presented as guidelines.

Authors
Shepard, SJ; Wang, J; Flynn, M; Gingold, E; Goldman, L; Krugh, K; Leong, DL; Mah, E; Ogden, K; Peck, D; Samei, E; Wang, J; Willis, CE
MLA Citation
Shepard, SJ, Wang, J, Flynn, M, Gingold, E, Goldman, L, Krugh, K, Leong, DL, Mah, E, Ogden, K, Peck, D, Samei, E, Wang, J, and Willis, CE. "An exposure indicator for digital radiography: AAPM Task Group 116 (executive summary)." Med Phys 36.7 (July 2009): 2898-2914.
PMID
19673189
Source
pubmed
Published In
Medical physics
Volume
36
Issue
7
Publish Date
2009
Start Page
2898
End Page
2914
DOI
10.1118/1.3121505

Pediatric MDCT: towards assessing the diagnostic influence of dose reduction on the detection of small lung nodules.

RATIONALE AND OBJECTIVES: The purpose of this study was to evaluate the effect of reduced tube current (dose) on lung nodule detection in pediatric multidetector array computed tomography (MDCT). MATERIALS AND METHODS: The study included normal clinical chest MDCT images of 13 patients (aged 1-7 years) scanned at tube currents of 70 to 180 mA. Calibrated noise addition software was used to simulate cases as they would have been acquired at 70 mA (the lowest original tube current), 35 mA (50% reduction), and 17.5 mA (75% reduction). Using a validated nodule simulation technique, small lung nodules of 3 to 5 mm in diameter were inserted into the cases, which were then randomized and rated independently by three experienced pediatric radiologists for nodule presence on a continuous scale ranging from zero (definitely absent) to 100 (definitely present). The observer data were analyzed to assess the influence of dose on detection accuracy using the Dorfman-Berbaum-Mets method for multiobserver, multitreatment receiver-operating characteristic (ROC) analysis and the Williams trend test. RESULTS: The areas under the ROC curves were 0.95, 0.91, and 0.92 at 70, 35, and 17.5 mA, respectively, with standard errors of 0.02 and interobserver variability of 0.02. The Dorfman-Berbaum-Mets method and the Williams trend test yielded P values for the effect of dose of .09 and .05, respectively. CONCLUSION: Tube current (dose) has a weak effect on the detection accuracy of small lung nodules in pediatric MDCT. The effect on detection accuracy of a 75% dose reduction was comparable to interobserver variability, suggesting a potential for dose reduction.

Authors
Li, X; Samei, E; DeLong, DM; Jones, RP; Gaca, AM; Hollingsworth, CL; Maxfield, CM; Colsher, JG; Frush, DP
MLA Citation
Li, X, Samei, E, DeLong, DM, Jones, RP, Gaca, AM, Hollingsworth, CL, Maxfield, CM, Colsher, JG, and Frush, DP. "Pediatric MDCT: towards assessing the diagnostic influence of dose reduction on the detection of small lung nodules." Acad Radiol 16.7 (July 2009): 872-880.
PMID
19394875
Source
pubmed
Published In
Academic Radiology
Volume
16
Issue
7
Publish Date
2009
Start Page
872
End Page
880
DOI
10.1016/j.acra.2009.01.028

Can compression be reduced for breast tomosynthesis? Monte carlo study on mass and microcalcification conspicuity in tomosynthesis.

PURPOSE: To assess, in a voxelized anthropomorphic breast phantom, how the conspicuity of breast masses and microcalcifications may be affected by applying reduced breast compression in tomosynthesis. MATERIALS AND METHODS: A breast tomosynthesis system was modeled by using a Monte Carlo program and a voxelized anthropomorphic breast phantom. The Monte Carlo program created simulated tomosynthesis projection images, which were reconstructed by using filtered back-projection software. Reconstructed images were analyzed for mass and microcalcification conspicuity, or the ratio of the lesion contrast to the anatomic and quantum noise surrounding the lesion. This analysis was performed at two compression levels (standard and 12.5% reduction) and for two breast compression thicknesses (4 and 6 cm). The change in conspicuity was analyzed for significance by using a bootstrap method and a paired Student t test. RESULTS: While keeping the glandular radiation dose constant with respective standard and reduced compression levels, the mean mass conspicuities were 1.39 +/- 0.15 (standard error of the mean) and 1.46 +/- 0.22 for a 4-cm breast compression phantom and 1.26 +/- 0.15 and 1.22 +/- 0.20 for a 6-cm breast phantom, and the mean microcalcification conspicuities were 16.2 +/- 2.87 and 18.6 +/- 2.63 for a 4-cm breast phantom and 11.4 +/- 1.11 and 10.6 +/- 1.18 for a 6-cm breast compression phantom. CONCLUSION: For constant glandular dose, mass and microcalcification conspicuity remained approximately constant with decreased compression. Constant conspicuity implies that reduced compression would have a minimal effect on radiologists' performance, which suggests that there is justification for a measured reduction of breast compression for breast tomosynthesis, increasing the comfort of women undergoing the examination.

Authors
Saunders, RS; Samei, E; Lo, JY; Baker, JA
MLA Citation
Saunders, RS, Samei, E, Lo, JY, and Baker, JA. "Can compression be reduced for breast tomosynthesis? Monte carlo study on mass and microcalcification conspicuity in tomosynthesis." Radiology 251.3 (June 2009): 673-682.
PMID
19474373
Source
pubmed
Published In
Radiology
Volume
251
Issue
3
Publish Date
2009
Start Page
673
End Page
682
DOI
10.1148/radiol.2521081278

Hypervascular liver tumors: low tube voltage, high tube current multidetector CT during late hepatic arterial phase for detection--initial clinical experience.

PURPOSE: To intraindividually compare a low tube voltage (80 kVp), high tube current computed tomographic (CT) technique with a standard CT protocol (140 kVp) in terms of image quality, radiation dose, and detection of malignant hypervascular liver tumors during the late hepatic arterial phase. MATERIALS AND METHODS: This prospective single-center HIPAA-compliant study had institutional review board approval, and written informed consent was obtained. Forty-eight patients (31 men, 17 women; age range, 35-77 years) with 60 malignant hypervascular liver tumors (mean diameter, 20.1 mm +/- 16.4 [standard deviation]) were enrolled. Pathologic proof of focal lesions was obtained with histopathologic analysis for 33 nodules and imaging follow-up after a minimum of 12 months for 27 nodules. Patients underwent dual-energy 64-section multi-detector row CT. By using vendor-specific software, two imaging protocols-140 kVp and 385 mA (protocol A) and 80 kVp and 675 mA (protocol B)-were compared during the late hepatic arterial phase of contrast enhancement. Paired t tests were used to compare tumor-to-liver contrast-to-noise ratio (CNR) for each lesion, mean image noise, and effective dose between the two data sets. Three readers qualitatively assessed the two data sets in a blinded and independent fashion. Lesion detection and characterization and reader confidence were recorded, as well as readers' subjective evaluations of image quality. Wilcoxon-Mann-Whitney statistical analysis was performed on this assessment. RESULTS: Image noise increased from 5.7 to 11.4 HU as the tube voltage decreased from 140 to 80 kVp (P < .0001), resulting in a significantly lower image quality score (4.0 vs 3.0, respectively) with protocol B according to all readers (P < .001). At the same time, protocol B yielded significantly higher CNR (8.2 vs 6.4) and lesion conspicuity scores (4.6 vs 4.1) than protocol A, along with a lower effective dose (5.1 vs 17.5 mSv) (P < .001 for all). CONCLUSION: By substantially increasing the tumor-to-liver CNR, a low tube voltage, high tube current CT technique improves the conspicuity of malignant hypervascular liver tumors during the late hepatic arterial phase while significantly reducing patient radiation dose.

Authors
Marin, D; Nelson, RC; Samei, E; Paulson, EK; Ho, LM; Boll, DT; DeLong, DM; Yoshizumi, TT; Schindera, ST
MLA Citation
Marin, D, Nelson, RC, Samei, E, Paulson, EK, Ho, LM, Boll, DT, DeLong, DM, Yoshizumi, TT, and Schindera, ST. "Hypervascular liver tumors: low tube voltage, high tube current multidetector CT during late hepatic arterial phase for detection--initial clinical experience." Radiology 251.3 (June 2009): 771-779.
PMID
19346514
Source
pubmed
Published In
Radiology
Volume
251
Issue
3
Publish Date
2009
Start Page
771
End Page
779
DOI
10.1148/radiol.2513081330

Three-dimensional simulation of lung nodules for paediatric multidetector array CT.

The purpose of this study was to develop and validate a technique for three-dimensional (3D) modelling of small lung nodules on paediatric multidetector array computed tomography (MDCT) images. Clinical images were selected from 21 patients (<18 years old) who underwent MDCT examinations. Sixteen of the patients had one or more real lung nodules with diameters between 2.5 and 6 mm. A mathematical simulation technique was developed to emulate the 3D characteristics of the real nodules. To validate this technique, MDCT images of 34 real nodules and 55 simulated nodules were randomised and rated independently by four experienced paediatric radiologists on a continuous scale of appearance between 0 (definitely not real) and 100 (definitely real). Receiver operating characteristic (ROC) analysis, t-test, and equivalence test were performed to assess the radiologists' ability to distinguish between simulated and real nodules. The two types of nodules were also compared in terms of measured shape and contrast profile irregularities. The areas under the ROC curves were 0.59, 0.60, 0.40, and 0.63 for the four observers. Mean score differences between simulated and real nodules were -8, -11, 13, and -4 for the four observers with p-values of 0.17, 0.06, 0.17, and 0.26, respectively. The simulated and real nodules were perceptually equivalent and had comparable shape and contrast profile irregularities. In conclusion, mathematical simulation is a feasible technique for creating realistic small lung nodules on paediatric MDCT images.

Authors
Li, X; Samei, E; Delong, DM; Jones, RP; Gaca, AM; Hollingsworth, CL; Maxfield, CM; Carrico, CWT; Frush, DP
MLA Citation
Li, X, Samei, E, Delong, DM, Jones, RP, Gaca, AM, Hollingsworth, CL, Maxfield, CM, Carrico, CWT, and Frush, DP. "Three-dimensional simulation of lung nodules for paediatric multidetector array CT." Br J Radiol 82.977 (May 2009): 401-411.
PMID
19153182
Source
pubmed
Published In
British Journal of Radiology
Volume
82
Issue
977
Publish Date
2009
Start Page
401
End Page
411
DOI
10.1259/bjr/51749983

Qualitative Effect of Gadolinium on Diffusion-Weighted MR Imaging of the Liver, Spleen, Pancreas and Kidney at 3T

Authors
Wang, C; Dale, B; Neville, A; Boll, D; Samei, E; Merkle, E
MLA Citation
Wang, C, Dale, B, Neville, A, Boll, D, Samei, E, and Merkle, E. "Qualitative Effect of Gadolinium on Diffusion-Weighted MR Imaging of the Liver, Spleen, Pancreas and Kidney at 3T." AMERICAN JOURNAL OF ROENTGENOLOGY 192.5 (May 2009).
Source
wos-lite
Published In
AJR. American journal of roentgenology
Volume
192
Issue
5
Publish Date
2009

Towards optimized acquisition scheme for multiprojection correlation imaging of breast cancer.

RATIONALE AND OBJECTIVES: Correlation imaging (CI) is a form of multiprojection imaging in which multiple images of a patient are acquired from slightly different angles. Information from these images is combined to make the final diagnosis. A critical factor affecting the performance of CI is its data acquisition scheme, because nonoptimized acquisition may distort pathologic indicators. The authors describe a computer-aided detection (CADe) methodology to optimize the acquisition scheme of CI for superior diagnostic accuracy. MATERIALS AND METHODS: Images from 106 subjects were used. For each subject, 25 angular projections of a single breast were acquired. Projection images were supplemented with a simulated 3-mm three-dimensional lesion. Each projection was then processed using a traditional CADe algorithm at high sensitivity, followed by the reduction of false-positives by combining the geometric correlation information available from the multiple images. The performance of the CI system was determined in terms of free-response receiver-operating characteristic curves and the areas under receiver-operating characteristic curves. For optimization, the components of acquisition, such as the number of projections and their angular span, were systematically changed to investigate which of the many possible combinations maximized the obtainable CADe sensitivity and specificity. RESULTS: The performance of the CI system was improved by increasing the angular span. Increasing the number of angular projections beyond a certain number did not improve performance. Maximum performance was obtained between 7 and 10 projections spanning a maximum angular arc of 45 degrees . CONCLUSION: The findings suggest the existence of an optimum acquisition scheme for CI of the breast. CADe results confirmed earlier predictions on the basis of observer models. An optimized CI system may be an important diagnostic tool for improved breast cancer detection.

Authors
Chawla, AS; Saunders, RS; Singh, S; Lo, JY; Samei, E
MLA Citation
Chawla, AS, Saunders, RS, Singh, S, Lo, JY, and Samei, E. "Towards optimized acquisition scheme for multiprojection correlation imaging of breast cancer." Acad Radiol 16.4 (April 2009): 456-463.
PMID
19268858
Source
pubmed
Published In
Academic Radiology
Volume
16
Issue
4
Publish Date
2009
Start Page
456
End Page
463
DOI
10.1016/j.acra.2008.09.013

The influence of increased ambient lighting on mass detection in mammograms.

RATIONALE AND OBJECTIVES: Recent research has provided evidence that in reading rooms equipped with liquid crystal displays (LCDs), a measured increase of ambient lighting may improve clinicians' detection performance. In agreement with this research, the American College of Radiology (ACR) has recommended a moderate increase of ambient lighting in mammography reading rooms. This study was designed to examine the effect of a controlled increase of ambient lighting in mammography reading rooms on the diagnostic performance of breast imaging radiologists. MATERIALS AND METHODS: Four breast imaging radiologists read 86 mammograms (43 containing subtle cancerous masses and 43 normal) under low (E = 1 lux) and elevated (E = 50 lux) ambient lighting levels on a Digital Imaging and Communications in Medicine-calibrated, medical-grade LCD. Radiologists were asked to identify cancerous masses and to rate their detection confidence. Observer areas under the curve (AUCs) were calculated using a receiver-operating characteristic analysis of fully paired results. Additionally, average observer selection times under both ambient lighting levels were determined. RESULTS: Average radiologist AUCs decreased with elevated ambient lighting (0.78 +/- 0.03 to 0.72 +/- 0.04). Observer performance differences, however, were of the same order of magnitude as interobserver variability and were not statistically significant. Average selection times under increased ambient lighting remained constant or decreased, with the greatest decrease occurring for false-positive (20.4 +/- 18.9 to 14.4 +/- 9.6 seconds) and true-positive (18.0 +/- 13.8 to 12.9 +/- 9.4 seconds) selections. CONCLUSION: The results agree with those of previous studies in that observer performance differences under a controlled increase of ambient lighting are not statistically significant. On the basis of these findings and ACR guidelines, a moderate increase of ambient lighting in mammography reading rooms is still suggested, but further research with additional cases and observers should be considered.

Authors
Pollard, BJ; Samei, E; Chawla, AS; Baker, J; Ghate, S; Kim, C; Soo, MS; Hashimoto, N
MLA Citation
Pollard, BJ, Samei, E, Chawla, AS, Baker, J, Ghate, S, Kim, C, Soo, MS, and Hashimoto, N. "The influence of increased ambient lighting on mass detection in mammograms." Acad Radiol 16.3 (March 2009): 299-304.
PMID
19201358
Source
pubmed
Published In
Academic Radiology
Volume
16
Issue
3
Publish Date
2009
Start Page
299
End Page
304
DOI
10.1016/j.acra.2008.08.017

Comparison of patient size-based methods for estimating quantum noise in CT images of the lung.

The authors explored four methods for estimating quantum noise in CT images of the lung, each based on a different definition of patient size (water-equivalent diameter) and the relationship between noise and diameter determined in water phantoms. The accuracies of the four methods were evaluated using an image-subtraction method as a gold standard. Noise estimates based on patient sizes derived from chest area, water-equivalent area, non-lung area, and water-equivalent path length had maximum errors of 229%, 93%, 34%, and 57%, respectively. Considering the magnitude of noise variation across the lung volume (approximately 30%), noise estimate based on non-lung area was reasonably accurate.

Authors
Li, X; Samei, E
MLA Citation
Li, X, and Samei, E. "Comparison of patient size-based methods for estimating quantum noise in CT images of the lung." Med Phys 36.2 (February 2009): 541-546.
PMID
19291993
Source
pubmed
Published In
Medical physics
Volume
36
Issue
2
Publish Date
2009
Start Page
541
End Page
546
DOI
10.1118/1.3058482

Mass detection on mammograms: influence of signal shape uncertainty on human and model observers.

We studied the influence of signal variability on human and model observers for detection tasks with realistic simulated masses superimposed on real patient mammographic backgrounds and synthesized mammographic backgrounds (clustered lumpy backgrounds, CLB). Results under the signal-known-exactly (SKE) paradigm were compared with signal-known-statistically (SKS) tasks for which the observers did not have prior knowledge of the shape or size of the signal. Human observers' performance did not vary significantly when benign masses were superimposed on real images or on CLB. Uncertainty and variability in signal shape did not degrade human performance significantly compared with the SKE task, while variability in signal size did. Implementation of appropriate internal noise components allowed the fit of model observers to human performance.

Authors
Castella, C; Eckstein, MP; Abbey, CK; Kinkel, K; Verdun, FR; Saunders, RS; Samei, E; Bochud, FO
MLA Citation
Castella, C, Eckstein, MP, Abbey, CK, Kinkel, K, Verdun, FR, Saunders, RS, Samei, E, and Bochud, FO. "Mass detection on mammograms: influence of signal shape uncertainty on human and model observers." J Opt Soc Am A Opt Image Sci Vis 26.2 (February 2009): 425-436.
PMID
19183697
Source
pubmed
Published In
Journal of the Optical Society of America A
Volume
26
Issue
2
Publish Date
2009
Start Page
425
End Page
436

Micro-CT imaging of breast tumors in rodents using a liposomal, nanoparticle contrast agent.

A long circulating liposomal, nanoscale blood pool agent encapsulating traditional iodinated contrast agent (65 mg I/mL) was used for micro-computed tomography (CT) imaging of rats implanted with R3230AC mammary carcinoma. Three-dimensional vascular architecture of tumors was imaged at 100-micron isotropic resolution. The image data showed good qualitative correlation with pathologic findings. The approach holds promise for studying tumor angiogenesis and for evaluating anti-angiogenesis therapies.

Authors
Samei, E; Saunders, RS; Badea, CT; Ghaghada, KB; Hedlund, LW; Qi, Y; Yuan, H; Bentley, RC; Mukundan, S
MLA Citation
Samei, E, Saunders, RS, Badea, CT, Ghaghada, KB, Hedlund, LW, Qi, Y, Yuan, H, Bentley, RC, and Mukundan, S. "Micro-CT imaging of breast tumors in rodents using a liposomal, nanoparticle contrast agent." Int J Nanomedicine 4 (2009): 277-282.
PMID
20011244
Source
pubmed
Published In
International journal of nanomedicine
Volume
4
Publish Date
2009
Start Page
277
End Page
282

Extension of DQE to include scatter, grid, magnification, and focal spot blur: A new experimental technique and metric

In digital radiography, conventional DQE evaluations are performed under idealized conditions that do not reflect typical clinical operating conditions. For this reason, we have developed and evaluated an experimental methodology for measuring the effective detective quantum efficiency (eDQE) of digital radiographic systems and its utility in chest imaging applications.To emulate the attenuation and scatter properties of the human thorax across a range of sizes, the study employed pediatric and adult geometric chest imaging phantoms designed for use in the FDA/CDRH Nationwide Evaluation of X-Ray Trends (NEXT) program and a third phantom configuration designed to represent the bariatric population. The MTF for each phantom configuration was measured using images of an opaque edge device placed at the nominal surface of each phantom and at a common reference point. For each phantom, the NNPS was measured in a uniform region within the phantom image acquired at an exposure level determined from a prior phototimed acquisition. Scatter measurements were made using a beam-stop technique. These quantities were used along with measures of phantom attenuation and estimates of x-ray flux, to compute the eDQE at the beam-entrance surface of the phantoms, reflecting the presence of scatter, grid, magnification, and focal spot blur. The MTF results showed notable degradation due to focal spot blurring enhanced by geometric magnification, with increasing phantom size. Measured scatter fractions were 33%, 34% and 46% for the pediatric, adult, and bariatric phantoms, respectively. Correspondingly, the measured narrow beam transmission fractions were 16%, 9%, and 3%. The eDQE results for the pediatric and adult phantoms correlate well at low spatial frequencies but show degradation in the eDQE at increasing spatial frequencies for the adult phantom in comparison to the pediatric phantom. The results for the bariatric configuration showed a marked decrease in eDQE in comparison to the adult phantom results, across all spatial frequencies, attributable to the combined differences in geometric magnification, and scatter. The eDQE metric has been demonstrated to be sensitive to body habitus suggesting its usefulness in assessing system response across a range of chest sizes and potentially making it a useful factor in protocol assessment and optimization.©2009 SPIE.

Authors
Ranger, NT; Mackenzie, A; Honey, ID; III, JTD; Ravin, CE; Samei, E
MLA Citation
Ranger, NT, Mackenzie, A, Honey, ID, III, JTD, Ravin, CE, and Samei, E. "Extension of DQE to include scatter, grid, magnification, and focal spot blur: A new experimental technique and metric." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 7258 (2009).
Source
scival
Published In
Proceedings of SPIE
Volume
7258
Publish Date
2009
DOI
10.1117/12.813779

Patient specific computerized phantoms to estimate dose in pediatric CT

We create a series of detailed computerized phantoms to estimate patient organ and effective dose in pediatric CT and investigate techniques for efficiently creating patient-specific phantoms based on imaging data. The initial anatomy of each phantom was previously developed based on manual segmentation of pediatric CT data. Each phantom was extended to include a more detailed anatomy based on morphing an existing adult phantom in our laboratory to match the framework (based on segmentation) defined for the target pediatric model. By morphing a template anatomy to match the patient data in the LDDMM framework, it was possible to create a patient specific phantom with many anatomical structures, some not visible in the CT data. The adult models contain thousands of defined structures that were transformed to define them in each pediatric anatomy. The accuracy of this method, under different conditions, was tested using a known voxelized phantom as the target. Errors were measured in terms of a distance map between the predicted organ surfaces and the known ones. We also compared calculated dose measurements to see the effect of different magnitudes of errors in morphing. Despite some variations in organ geometry, dose measurements from morphing predictions were found to agree with those calculated from the voxelized phantom thus demonstrating the feasibility of our methods. © 2009 SPIE.

Authors
Segars, WP; Sturgeon, G; Li, X; Cheng, L; Ceritoglu, C; Ratnanather, JT; Miller, MI; Tsui, BMW; Frush, D; Samei, E
MLA Citation
Segars, WP, Sturgeon, G, Li, X, Cheng, L, Ceritoglu, C, Ratnanather, JT, Miller, MI, Tsui, BMW, Frush, D, and Samei, E. "Patient specific computerized phantoms to estimate dose in pediatric CT." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 7258 (2009).
Source
scival
Published In
Proceedings of SPIE
Volume
7258
Publish Date
2009
DOI
10.1117/12.813517

Patient-specific dose estimation for pediatric abdomen-pelvisCT

The purpose of this study is to develop a method for estimating patient-specific dose from abdomen-pelvis CT examinations and to investigate dose variation across patients in the same weight group. Our study consisted of seven pediatric patients in the same weight/protocol group, for whom full-body computer models were previously created based on the patients' CT data obtained for clinical indications. Organ and effective dose of these patients from an abdomen-pelvis scan protocol (LightSpeed VCT scanner, 120- kVp, 85-90 mA, 0.4-s gantry rotation period, 1.375-pitch, 40-mm beam collimation, and small body scan field-of-view) was calculated using a Monte Carlo program previously developed and validated for the same CT system. The seven patients had effective dose of 2.4-2.8 mSv, corresponding to normalized effective dose of 6.6-8.3 mSv/100mAs (coefficient of variation: 7.6%). Dose variations across the patients were small for large organs in the scan coverage (mean: 6.6%; range: 4.9%-9.2%), larger for small organs in the scan coverage (mean: 10.3%; range: 1.4%-15.6%), and the largest for organs partially or completely outside the scan coverage (mean: 14.8%; range: 5.7%-27.7%). Normalized effective dose correlated strongly with body weight (correlation coefficient: r = -0.94). Normalized dose to the kidney and the adrenal gland correlated strongly with mid-liver equivalent diameter (kidney: r = -0.97; adrenal glands: r = -0.98). Normalized dose to the small intestine correlated strongly with mid-intestine equivalent diameter (r = -0.97). These strong correlations suggest that patient-specific dose may be estimated for any other child in the same size group who undergoes the abdomen-pelvis scan. © 2009 SPIE.

Authors
Li, X; Samei, E; Segars, WP; Sturgeon, GM; Colsher, JG; Frush, DP
MLA Citation
Li, X, Samei, E, Segars, WP, Sturgeon, GM, Colsher, JG, and Frush, DP. "Patient-specific dose estimation for pediatric abdomen-pelvisCT." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 7258 (2009).
Source
scival
Published In
Proceedings of SPIE
Volume
7258
Publish Date
2009
DOI
10.1117/12.813531

Optimized lesion detection in breast tomosynthesis

While diagnostic improvement via breast tomosynthesis has been notable, the full potential of tomosynthesis has not yet been realized. This is because of the complex task of optimizing multiple parameters that constitute image acquisition and thus affect tomosynthesis performance. Those parameters include dose, number of angular projections, and the total angular span of those projections. In this study, we investigated the effects of acquisition parameters, independent of each other, on the overall diagnostic image quality of tomosynthesis. Five mastectomy specimens were imaged using a prototype tomosynthesis system. 25 angular projections of each specimen were acquired at 6.2 times typical single-view mammographic dose level. Images at lower dose levels were then simulated using a noise modification routine. Each projection image was supplemented with 84 simulated 3 mm 3D lesions embedded at the center of 84 non-overlapping ROIs. The projection images were then reconstructed using a filtered-back projection (FBP) algorithm at 224 different combinations of acquisition parameters to investigate which one of the many possible combinations maximized performance. Performance was evaluated in terms of a Laguerre-Gauss channelized Hotelling observer model-based measure of lesion detectability. Results showed that performance improved with an increase in the total acquisition dose level and the angular span. At a constant dose level and angular span, the performance rolled-off beyond a certain number of projections, indicating that simply increasing the number of projections in tomosynthesis may not necessarily improve its performance. The best performance was obtained with 15-17 projections spanning an angular arc of ~45° - the maximum tested in our study, and for an acquisition dose equal to single-view mammography. The optimization framework developed in this framework is applicable to other reconstruction techniques and other multi-projection systems. © 2009 SPIE.

Authors
Chawla, AS; Samei, E; Lo, JY
MLA Citation
Chawla, AS, Samei, E, and Lo, JY. "Optimized lesion detection in breast tomosynthesis." 2009.
Source
scival
Published In
Proceedings of SPIE
Volume
7258
Publish Date
2009
DOI
10.1117/12.813964

Design and development of a new multi-projection X-ray system for chest imaging

Overlapping anatomical structures may confound the detection of abnormal pathology, including lung nodules, in conventional single-projection chest radiography. To minimize this fundamental limiting factor, a dedicated digital multi-projection system for chest imaging was recently developed at the Radiology Department of Duke University. We are reporting the design of the multi-projection imaging system and its initial performance in an ongoing clinical trial. The system is capable of acquiring multiple full-field projections of the same patient along both the horizontal and vertical axes at variable speeds and acquisition frame rates. These images acquired in rapid succession from slightly different angles about the posterior-anterior (PA) orientation can be correlated to minimize the influence of overlying anatomy. The developed system has been tested for repeatability and motion blur artifacts to investigate its robustness for clinical trials. Excellent geometrical consistency was found in the tube motion, with positional errors for clinical settings within 1%. The effect of tube-motion on the image quality measured in terms of impact on the Modulation Transfer Function (MTF) was found to be minimal. The system was deemed clinic-ready and a clinical trial was subsequently launched. The flexibility of image acquisition built into the system provides a unique opportunity to easily modify it for different clinical applications, including tomosynthesis, correlation imaging (CI), and stereoscopic imaging. © 2006 IEEE.

Authors
Chawla, AS; Boyce, S; Washington, L; McAdams, HP; Samei, E
MLA Citation
Chawla, AS, Boyce, S, Washington, L, McAdams, HP, and Samei, E. "Design and development of a new multi-projection X-ray system for chest imaging." IEEE Transactions on Nuclear Science 56.1 (2009): 36-45.
Source
scival
Published In
IEEE Transactions on Nuclear Science
Volume
56
Issue
1
Publish Date
2009
Start Page
36
End Page
45
DOI
10.1109/TNS.2008.2008647

Contrast detail curves in head ct examinations

The purpose of this study was to generate contrast detail (CD) curves for low contrast mass lesions embedded in images obtained in head and neck CT examinations. Axial head and neck CT slice images were randomly chosen from patients at five different levels. All images were acquired at 120 kV, and reconstructed using a standard soft tissue reconstruction filter. For each head CT image, we measured detection of low contrast mass lesions using a 2 Alternate Forced Choice (2-AFC) experimental paradigm. In an AFC experiment, an observer identifies the lesion location in one of two regions of interest. After performing 128 sequential observations, it is possible to compute the lesion contrast corresponding to a 92% accuracy of lesion detection (i.e., I92%). Five lesion sizes were investigated ranging from 4 mm to 12.5 mm, with the experimental order randomized to eliminate learning curve as well as observer fatigue. Contrast detail curves were generated by plotting log[I92%] versus log[lesion size]. Experimental slopes ranged from ~ -0.1 to ~ -0.4. The slope of the CD curve was directly related to the complexity of the anatomical structure in the head CT image. As the apparent anatomical complexity increased, the slope of the corresponding CD curve was reduced. Results from our pilot study suggest that anatomical structure is of greater importance than quantum mottle, and that the type of anatomical background structure is an important determinant of lesion detection in CT imaging.

Authors
Elojeimy, S; Huda, W; Ogden, KM; Owen, R; Samei, E; Rumboldt, Z
MLA Citation
Elojeimy, S, Huda, W, Ogden, KM, Owen, R, Samei, E, and Rumboldt, Z. "Contrast detail curves in head ct examinations." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 7263 (2009).
Source
scival
Published In
Proceedings of SPIE
Volume
7263
Publish Date
2009
DOI
10.1117/12.811660

The effect of dose reductions on lesion detection in head CT

The purpose of this study was to quantitatively evaluate the effect of reducing radiation dose (i.e., mAs) on lesion detection in head CT examinations. We used a simulation package (Syngo Explorer) to reconstruct 5-mm thick CT images of the brain of one patient pertaining to the centrum semiovale, the basal ganglia, and the sella turcica. Lesion detection was measured using two Alternate Forced Choice (2-AFC) experiments that measure the lesion contrast (I 92%) corresponding to a detection accuracy of 92%. Two observers performed experiments to investigate detection of low contrast lesions with four sizes ranging from 3 mm to 10 mm and at four x-ray beam intensities ranging from 105 mAs to 300 mAs. Results were plotted as log[I 92%] versus log[mAs], and the slopes were measured for each lesion size. Lowering the mAs always reduced lesion detection performance in all images, and for all lesion sizes. Average slopes of the I 92% versus mAs curves were -0.23 for 3 mm lesions,-0.16 for 4.5 mm lesions, and ∼-0.11 for the 7 and 10 mm lesions. For the smallest lesions investigated (3 mm), doubling the x-ray intensity improved lesion detection performance by ∼ 15%, whereas for the largest sized lesions (7 and 10 mm), doubling the tube current improved lesion detection performance by ∼ 7%. The observed improvements in detection performance are markedly lower than predicted by the Rose model where a doubling of the tube current would be expected to improve detection performance by 29% at all lesion sizes. © 2009 SPIE.

Authors
Elojeimy, S; Huda, W; Ogden, KM; Owen, R; Samei, E; Rumboldt, Z
MLA Citation
Elojeimy, S, Huda, W, Ogden, KM, Owen, R, Samei, E, and Rumboldt, Z. "The effect of dose reductions on lesion detection in head CT." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 7258 (2009).
Source
scival
Published In
Proceedings of SPIE
Volume
7258
Publish Date
2009
DOI
10.1117/12.812051

Use of effective detective quantum efficiency to optimise radiographic exposures for chest imaging with computed radiography

The purpose of the work was to test if effective detective quantum efficiency (eDQE) could be useful for optimisation of radiographic factors for computed radiography (CR) for adult chest examinations. The eDQE was therefore measured across a range of kilovoltage, with and without an anti-scatter grid. The modulation transfer function, noise power spectra, transmission factor and scatter fraction were measured with a phantom made of sheets of Aluminum and Acrylic. The entrance air kerma was selected to give an effective dose of 4.9 ìSv. The effective noise equivalent quanta (eNEQ) is introduced in this work. eNEQ can be considered equal to the number of X-ray quanta equivalent in the image corrected for the amount of scatter and the blurring processes. The eNEQ was then normalised to account for slight differences in the effective dose (eNEQED). The peak eNEQED was largest at 80 kV and 100 kV with no grid and with grid respectively. At each kilovoltage, the eNEQED and eDQE were between 10% and 70% larger when the grid was not used. The results show that 80 kV without grid is the most suitable exposure conditions for CR in chest. This is consistent with clinical practice in the UK and previous publications recommending a low kV technique for CR for average sized adult chest imaging. © 2009 SPIE.

Authors
Ertan, F; Mackenzie, A; Urbanczyk, HJ; Ranger, NT; Samei, E
MLA Citation
Ertan, F, Mackenzie, A, Urbanczyk, HJ, Ranger, NT, and Samei, E. "Use of effective detective quantum efficiency to optimise radiographic exposures for chest imaging with computed radiography." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 7258 (2009).
Source
scival
Published In
Proceedings of SPIE
Volume
7258
Publish Date
2009
DOI
10.1117/12.813650

Patient-specific dose estimation for pediatric chest CT.

Current methods for organ and effective dose estimations in pediatric CT are largely patient generic. Physical phantoms and computer models have only been developed for standard/limited patient sizes at discrete ages (e.g., 0, 1, 5, 10, 15 years old) and do not reflect the variability of patient anatomy and body habitus within the same size/age group. In this investigation, full-body computer models of seven pediatric patients in the same size/protocol group (weight: 11.9-18.2 kg) were created based on the patients' actual multi-detector array CT (MDCT) data. Organs and structures in the scan coverage were individually segmented. Other organs and structures were created by morphing existing adult models (developed from visible human data) to match the framework defined by the segmented organs, referencing the organ volume and anthropometry data in ICRP Publication 89. Organ and effective dose of these patients from a chest MDCT scan protocol (64 slice LightSpeed VCT scanner, 120 kVp, 70 or 75 mA, 0.4 s gantry rotation period, pitch of 1.375, 20 mm beam collimation, and small body scan field-of-view) was calculated using a Monte Carlo program previously developed and validated to simulate radiation transport in the same CT system. The seven patients had normalized effective dose of 3.7-5.3 mSv/100 mAs (coefficient of variation: 10.8%). Normalized lung dose and heart dose were 10.4-12.6 mGy/100 mAs and 11.2-13.3 mGy/100 mAs, respectively. Organ dose variations across the patients were generally small for large organs in the scan coverage (<7%), but large for small organs in the scan coverage (9%-18%) and for partially or indirectly exposed organs (11%-77%). Normalized effective dose correlated weakly with body weight (correlation coefficient: r=-0.80). Normalized lung dose and heart dose correlated strongly with mid-chest equivalent diameter (lung: r=-0.99, heart: r=-0.93); these strong correlation relationships can be used to estimate patient-specific organ dose for any other patient in the same size/protocol group who undergoes the chest scan. In summary, this work reported the first assessment of dose variations across pediatric CT patients in the same size/protocol group due to the variability of patient anatomy and body habitus and provided a previously unavailable method for patient-specific organ dose estimation, which will help in assessing patient risk and optimizing dose reduction strategies, including the development of scan protocols.

Authors
Li, X; Samei, E; Segars, WP; Sturgeon, GM; Colsher, JG; Frush, DP
MLA Citation
Li, X, Samei, E, Segars, WP, Sturgeon, GM, Colsher, JG, and Frush, DP. "Patient-specific dose estimation for pediatric chest CT." Med Phys 35.12 (December 2008): 5821-5828. (Letter)
PMID
19175138
Source
pubmed
Published In
Medical physics
Volume
35
Issue
12
Publish Date
2008
Start Page
5821
End Page
5828
DOI
10.1118/1.3026593

Detector or system? Extending the concept of detective quantum efficiency to characterize the performance of digital radiographic imaging systems.

PURPOSE: To develop an experimental method for measuring the effective detective quantum efficiency (eDQE) of digital radiographic imaging systems and evaluate its use in select imaging systems. MATERIALS AND METHODS: A geometric phantom emulating the attenuation and scatter properties of the adult human thorax was employed to assess eight imaging systems in a total of nine configurations. The noise power spectrum (NPS) was derived from images of the phantom acquired at three exposure levels spanning the operating range of the system. The modulation transfer function (MTF) was measured by using an edge device positioned at the anterior surface of the phantom. Scatter measurements were made by using a beam-stop technique. All measurements, including those of phantom attenuation and estimates of x-ray flux, were used to compute the eDQE. RESULTS: The MTF results showed notable degradation owing to focal spot blur. Scatter fractions ranged between 11% and 56%, depending on the system. The eDQE(0) results ranged from 1%-17%, indicating a reduction of up to one order of magnitude and different rank ordering and performance among systems, compared with that implied in reported conventional detective quantum efficiency results from the same systems. CONCLUSION: The eDQE method was easy to implement, yielded reproducible results, and provided a meaningful reflection of system performance by quantifying image quality in a clinically relevant context. The difference in the magnitude of the measured eDQE and the ideal eDQE of 100% provides a great opportunity for improving the image quality of radiographic and mammographic systems while reducing patient dose.

Authors
Samei, E; Ranger, NT; MacKenzie, A; Honey, ID; Dobbins, JT; Ravin, CE
MLA Citation
Samei, E, Ranger, NT, MacKenzie, A, Honey, ID, Dobbins, JT, and Ravin, CE. "Detector or system? Extending the concept of detective quantum efficiency to characterize the performance of digital radiographic imaging systems." Radiology 249.3 (December 2008): 926-937.
PMID
19011189
Source
pubmed
Published In
Radiology
Volume
249
Issue
3
Publish Date
2008
Start Page
926
End Page
937
DOI
10.1148/radiol.2492071734

The effect of breast compression on mass conspicuity in digital mammography.

This study analyzed how the inherent quality of diagnostic information in digital mammography could be affected by breast compression. A digital mammography system was modeled using a Monte Carlo algorithm based on the Penelope program, which has been successfully used to model several medical imaging systems. First, the Monte Carlo program was validated against previous measurements and simulations. Once validated, the Monte Carlo software modeled a digital mammography system by tracking photons through a voxelized software breast phantom, containing anatomical structures and breast masses, and following photons until they were absorbed by a selenium-based flat-panel detector. Simulations were performed for two compression conditions (standard compression and 12.5% reduced compression) and three photon flux conditions (constant flux, constant detector signal, and constant glandular dose). The results showed that reduced compression led to higher scatter fractions, as expected. For the constant photon flux condition, decreased compression also reduced glandular dose. For constant glandular dose, the SdNR for a 4 cm breast was 0.60 +/- 0.11 and 0.62 +/- 0.11 under standard and reduced compressions, respectively. For the 6 cm case with constant glandular dose, the SdNR was 0.50 +/- 0.11 and 0.49 +/- 0.10 under standard and reduced compressions, respectively. The results suggest that if a particular imaging system can handle an approximately 10% increase in total tube output and 10% decrease in detector signal, breast compression can be reduced by about 12% in terms of breast thickness with little impact on image quality or dose.

Authors
Saunders, RS; Samei, E
MLA Citation
Saunders, RS, and Samei, E. "The effect of breast compression on mass conspicuity in digital mammography." Med Phys 35.10 (October 2008): 4464-4473.
PMID
18975694
Source
pubmed
Published In
Medical physics
Volume
35
Issue
10
Publish Date
2008
Start Page
4464
End Page
4473
DOI
10.1118/1.2977600

Automated breast mass detection in 3D reconstructed tomosynthesis volumes: a featureless approach.

The purpose of this study was to propose and implement a computer aided detection (CADe) tool for breast tomosynthesis. This task was accomplished in two stages-a highly sensitive mass detector followed by a false positive (FP) reduction stage. Breast tomosynthesis data from 100 human subject cases were used, of which 25 subjects had one or more mass lesions and the rest were normal. For stage 1, filter parameters were optimized via a grid search. The CADe identified suspicious locations were reconstructed to yield 3D CADe volumes of interest. The first stage yielded a maximum sensitivity of 93% with 7.7 FPs/breast volume. Unlike traditional CADe algorithms in which the second stage FP reduction is done via feature extraction and analysis, instead information theory principles were used with mutual information as a similarity metric. Three schemes were proposed, all using leave-one-case-out cross validation sampling. The three schemes, A, B, and C, differed in the composition of their knowledge base of regions of interest (ROIs). Scheme A's knowledge base was comprised of all the mass and FP ROIs generated by the first stage of the algorithm. Scheme B had a knowledge base that contained information from mass ROIs and randomly extracted normal ROIs. Scheme C had information from three sources of information-masses, FPs, and normal ROIs. Also, performance was assessed as a function of the composition of the knowledge base in terms of the number of FP or normal ROIs needed by the system to reach optimal performance. The results indicated that the knowledge base needed no more than 20 times as many FPs and 30 times as many normal ROIs as masses to attain maximal performance. The best overall system performance was 85% sensitivity with 2.4 FPs per breast volume for scheme A, 3.6 FPs per breast volume for scheme B, and 3 FPs per breast volume for scheme C.

Authors
Singh, S; Tourassi, GD; Baker, JA; Samei, E; Lo, JY
MLA Citation
Singh, S, Tourassi, GD, Baker, JA, Samei, E, and Lo, JY. "Automated breast mass detection in 3D reconstructed tomosynthesis volumes: a featureless approach." Med Phys 35.8 (August 2008): 3626-3636.
PMID
18777923
Source
pubmed
Published In
Medical physics
Volume
35
Issue
8
Publish Date
2008
Start Page
3626
End Page
3636
DOI
10.1118/1.2953562

Introduction to grayscale calibration and related aspects of medical imaging grade liquid crystal displays.

Consistent presentation of digital radiographic images at all locations within a medical center can help ensure a high level of patient care. Currently, liquid crystal displays (LCDs) are the electronic display technology of choice for viewing medical images. As the inherent luminance (and thereby perceived contrast) properties of different LCDs can vary substantially, calibration of the luminance response of these displays is required to ensure that observer perception of an image is consistent on all displays. The digital imaging and communication in medicine (DICOM) grayscale standard display function (GSDF) defines the luminance response of a display such that an observer's perception of image contrast is consistent throughout the pixel value range of a displayed image. The main purpose of this work is to review the theoretical and practical aspects of calibration of LCDs to the GSDF. Included herein is a review of LCD technology, principles of calibration, and other practical aspects related to calibration and observer perception of images presented on LCDs. Both grayscale and color displays are considered, and the influence of ambient light on calibration and perception is discussed.

Authors
Fetterly, KA; Blume, HR; Flynn, MJ; Samei, E
MLA Citation
Fetterly, KA, Blume, HR, Flynn, MJ, and Samei, E. "Introduction to grayscale calibration and related aspects of medical imaging grade liquid crystal displays." J Digit Imaging 21.2 (June 2008): 193-207.
PMID
17333412
Source
pubmed
Published In
Journal of Digital Imaging
Volume
21
Issue
2
Publish Date
2008
Start Page
193
End Page
207
DOI
10.1007/s10278-007-9022-y

Object detectability at increased ambient lighting conditions.

Under typical dark conditions encountered in diagnostic reading rooms, a reader's pupils will contract and dilate as the visual focus intermittently shifts between the high luminance display and the darker background wall, resulting in increased visual fatigue and the degradation of diagnostic performance. A controlled increase of ambient lighting may, however, reduce the severity of these pupillary adjustments by minimizing the difference between the luminance level to which the eyes adapt while viewing an image (L(adp)) and the luminance level of diffusely reflected light from the area surrounding the display (L(s)). Although ambient lighting in reading rooms has conventionally been kept at a minimum to maintain the perceived contrast of film images, proper Digital Imaging and Communications in Medicine (DICOM) calibration of modern medical-grade liquid crystal displays can compensate for minor lighting increases with very little loss of image contrast. This paper describes two psychophysical studies developed to evaluate and refine optimum reading room ambient lighting conditions through the use of observational tasks intended to simulate real clinical practices. The first study utilized the biologic contrast response of the human visual system to determine a range of representative L(adp) values for typical medical images. Readers identified low contrast horizontal objects in circular foregrounds of uniform luminance (5, 12, 20, and 30 cd/m2) embedded within digitized mammograms. The second study examined the effect of increased ambient lighting on the detection of subtle objects embedded in circular foregrounds of uniform luminance (5, 12, and 35 cd/m2) centered within a constant background of 12 cd/m2 luminance. The images were displayed under a dark room condition (1 lux) and an increased ambient lighting level (50 lux) such that the luminance level of the diffusely reflected light from the background wall was approximately equal to the image L(adp) value of 12 cd/m2. Results from the first study demonstrated that observer true positive and false positive detection rates and true positive detection times were considerably better while viewing foregrounds at 12 and 20 cd/m2 than at the other foreground luminance levels. Results from the second study revealed that under increased room illuminance, the average true positive detection rate improved a statistically significant amount from 39.3% to 55.6% at 5 cd/m2 foreground luminance. Additionally, the true positive rate increased from 46.4% to 56.6% at 35 cd/m2 foreground luminance, and decreased slightly from 90.2% to 87.5% at 12 cd/m2 foreground luminance. False positive rates at all foreground luminance levels remained approximately constant with increased ambient lighting. Furthermore, under increased room illuminance, true positive detection times declined at every foreground luminance level, with the most considerable decrease (approximately 500 ms) at the 5 cd/m2 foreground luminance. The first study suggests that L(adp) of typical mammograms lies between 12 and 20 cd/m2, leading to an optimum reading room illuminance of approximately 50-80 lux. Findings from the second study provide psychophysical evidence that ambient lighting may be increased to a level within this range, potentially improving radiologist comfort, without deleterious effects on diagnostic performance.

Authors
Pollard, BJ; Chawla, AS; Delong, DM; Hashimoto, N; Samei, E
MLA Citation
Pollard, BJ, Chawla, AS, Delong, DM, Hashimoto, N, and Samei, E. "Object detectability at increased ambient lighting conditions." Med Phys 35.6 (June 2008): 2204-2213.
PMID
18649449
Source
pubmed
Published In
Medical physics
Volume
35
Issue
6
Publish Date
2008
Start Page
2204
End Page
2213
DOI
10.1118/1.2907566

Optimization of exposure parameters in full field digital mammography.

Optimization of exposure parameters (target, filter, and kVp) in digital mammography necessitates maximization of the image signal-to-noise ratio (SNR), while simultaneously minimizing patient dose. The goal of this study is to compare, for each of the major commercially available full field digital mammography (FFDM) systems, the impact of the selection of technique factors on image SNR and radiation dose for a range of breast thickness and tissue types. This phantom study is an update of a previous investigation and includes measurements on recent versions of two of the FFDM systems discussed in that article, as well as on three FFDM systems not available at that time. The five commercial FFDM systems tested, the Senographe 2000D from GE Healthcare, the Mammomat Novation DR from Siemens, the Selenia from Hologic, the Fischer Senoscan, and Fuji's 5000MA used with a Lorad M-IV mammography unit, are located at five different university test sites. Performance was assessed using all available x-ray target and filter combinations and nine different phantom types (three compressed thicknesses and three tissue composition types). Each phantom type was also imaged using the automatic exposure control (AEC) of each system to identify the exposure parameters used under automated image acquisition. The figure of merit (FOM) used to compare technique factors is the ratio of the square of the image SNR to the mean glandular dose. The results show that, for a given target/filter combination, in general FOM is a slowly changing function of kVp, with stronger dependence on the choice of target/filter combination. In all cases the FOM was a decreasing function of kVp at the top of the available range of kVp settings, indicating that higher tube voltages would produce no further performance improvement. For a given phantom type, the exposure parameter set resulting in the highest FOM value was system specific, depending on both the set of available target/filter combinations, and on the receptor type. In most cases, the AECs of the FFDM systems successfully identified exposure parameters resulting in FOM values near the maximum ones, however, there were several examples where AEC performance could be improved.

Authors
Williams, MB; Raghunathan, P; More, MJ; Seibert, JA; Kwan, A; Lo, JY; Samei, E; Ranger, NT; Fajardo, LL; McGruder, A; McGruder, SM; Maidment, ADA; Yaffe, MJ; Bloomquist, A; Mawdsley, GE
MLA Citation
Williams, MB, Raghunathan, P, More, MJ, Seibert, JA, Kwan, A, Lo, JY, Samei, E, Ranger, NT, Fajardo, LL, McGruder, A, McGruder, SM, Maidment, ADA, Yaffe, MJ, Bloomquist, A, and Mawdsley, GE. "Optimization of exposure parameters in full field digital mammography." Med Phys 35.6 (June 2008): 2414-2423.
PMID
18649474
Source
pubmed
Published In
Medical physics
Volume
35
Issue
6
Publish Date
2008
Start Page
2414
End Page
2423
DOI
10.1118/1.2912177

A comparative contrast-detail study of five medical displays.

The objective of this study was to compare the contrast-detail performance of five different commercial liquid crystal displays (LCDs) to other LCD and cathode-ray tube (CRT) displays for medical applications. A contrast-detail phantom, supplemented with 5 in. of acrylic, was imaged on a commercial digital radiographic system using techniques comparable to chest radiography. The phantom design enabled observer evaluation by a four-alternative forced choice paradigm. The acquired images were independently scored by five observers on five medical display devices: a 5 megapixel monochrome LCD, a 3 megapixel monochrome LCD, a 9 megapixel color LCD, a 5 megapixel monochrome CRT, and a mammographic-grade monochrome CRT. The data were analyzed using the method suggested by the manufacturer based on a nearest neighbor correction technique. They were further analyzed using a logistic regression response model with a natural threshold using an overall chi-square test for display type followed by pairwise comparisons for individual display performance. The differences between the display devices were small. The standard analysis of the results based on the manufacturer-recommended method did not yield any statistically discernible trend among displays. The logistic regression analysis, however, indicated that the 5 megapixel monochrome LCD was statistically significantly (p <0.0001) superior to the others, followed by the 3 megapixel monochrome LCD (p<0.0001). The three other displays exhibited lower but generally similar performance characteristics. The findings suggest that 5 and 3 megapixel monochrome LCDs provide comparable but subtly superior contrast detectability than other tested displays, with the former performing slightly better in the detection of subtle and fine details.

Authors
Samei, E; Ranger, NT; Delong, DM
MLA Citation
Samei, E, Ranger, NT, and Delong, DM. "A comparative contrast-detail study of five medical displays." Med Phys 35.4 (April 2008): 1358-1364.
PMID
18491530
Source
pubmed
Published In
Medical physics
Volume
35
Issue
4
Publish Date
2008
Start Page
1358
End Page
1364
DOI
10.1118/1.2868780

A mathematical model platform for optimizing a multiprojection breast imaging system.

Multiprojection imaging is a technique in which a plurality of digital radiographic images of the same patient are acquired within a short interval of time from slightly different angles. Information from each image is combined to determine the final diagnosis. Projection data are either reconstructed into slices as in the case of tomosynthesis or analyzed directly as in the case of multiprojection correlation imaging technique, thereby avoiding reconstruction artifacts. In this study, the authors investigated the optimum geometry of acquisitions of a multiprojection breast correlation imaging system in terms of the number of projections and their total angular span that yield maximum performance in a task that models clinical decision. Twenty-five angular projections of each breast from 82 human subjects in our breast tomosynthesis database were each supplemented with a simulated 3 mm mass. An approach based on Laguerre-Gauss channelized Hotelling observer was developed to assess the detectability of the mass in terms of receiver operating characteristic (ROC) curves. Two methodologies were developed to integrate results from individual projections into one combined ROC curve as the overall figure of merit. To optimize the acquisition geometry, different components of acquisitions were changed to investigate which one of the many possible configurations maximized the area under the combined ROC curve. Optimization was investigated under two acquisition dose conditions corresponding to a fixed total dose delivered to the patient and a variable dose condition, based on the number of projections used. In either case, the detectability was dependent on the number of projections used, the total angular span of those projections, and the acquisition dose level. In the first case, the detectability approximately followed a bell curve as a function of the number of projections with the maximum between 8 and 16 projections spanning angular arcs of about 23 degrees-45 degrees, respectively. In the second case, the detectability increased with the number of projections approaching an asymptote at 11-17 projections for an angular span of about 45 degrees. These results indicate the inherent information content of the multi-projection image data reflecting the relative role of quantum and anatomical noise in multiprojection breast imaging. The optimization scheme presented here may be applied to any multiprojection imaging modalities and may be extended by including reconstruction in the case of digital breast tomosynthesis and breast computed tomography.

Authors
Chawla, AS; Samei, E; Saunders, RS; Lo, JY; Baker, JA
MLA Citation
Chawla, AS, Samei, E, Saunders, RS, Lo, JY, and Baker, JA. "A mathematical model platform for optimizing a multiprojection breast imaging system." Med Phys 35.4 (April 2008): 1337-1345.
PMID
18491528
Source
pubmed
Published In
Medical physics
Volume
35
Issue
4
Publish Date
2008
Start Page
1337
End Page
1345
DOI
10.1118/1.2885367

Hypervascular liver tumors: low tube voltage, high tube current multi-detector row CT for enhanced detection--phantom study.

PURPOSE: To prospectively evaluate, for the depiction of simulated hypervascular liver lesions in a phantom, the effect of a low tube voltage, high tube current computed tomographic (CT) technique on image noise, contrast-to-noise ratio (CNR), lesion conspicuity, and radiation dose. MATERIALS AND METHODS: A custom liver phantom containing 16 cylindric cavities (four cavities each of 3, 5, 8, and 15 mm in diameter) filled with various iodinated solutions to simulate hypervascular liver lesions was scanned with a 64-section multi-detector row CT scanner at 140, 120, 100, and 80 kVp, with corresponding tube current-time product settings at 225, 275, 420, and 675 mAs, respectively. The CNRs for six simulated lesions filled with different iodinated solutions were calculated. A figure of merit (FOM) for each lesion was computed as the ratio of CNR2 to effective dose (ED). Three radiologists independently graded the conspicuity of 16 simulated lesions. An anthropomorphic phantom was scanned to evaluate the ED. Statistical analysis included one-way analysis of variance. RESULTS: Image noise increased by 45% with the 80-kVp protocol compared with the 140-kVp protocol (P < .001). However, the lowest ED and the highest CNR were achieved with the 80-kVp protocol. The FOM results indicated that at a constant ED, a reduction of tube voltage from 140 to 120, 100, and 80 kVp increased the CNR by factors of at least 1.6, 2.4, and 3.6, respectively (P < .001). At a constant CNR, corresponding reductions in ED were by a factor of 2.5, 5.5, and 12.7, respectively (P < .001). The highest lesion conspicuity was achieved with the 80-kVp protocol. CONCLUSION: The CNR of simulated hypervascular liver lesions can be substantially increased and the radiation dose reduced by using an 80-kVp, high tube current CT technique.

Authors
Schindera, ST; Nelson, RC; Mukundan, S; Paulson, EK; Jaffe, TA; Miller, CM; DeLong, DM; Kawaji, K; Yoshizumi, TT; Samei, E
MLA Citation
Schindera, ST, Nelson, RC, Mukundan, S, Paulson, EK, Jaffe, TA, Miller, CM, DeLong, DM, Kawaji, K, Yoshizumi, TT, and Samei, E. "Hypervascular liver tumors: low tube voltage, high tube current multi-detector row CT for enhanced detection--phantom study." Radiology 246.1 (January 2008): 125-132.
PMID
18096533
Source
pubmed
Published In
Radiology
Volume
246
Issue
1
Publish Date
2008
Start Page
125
End Page
132
DOI
10.1148/radiol.2461070307

Utility of a prototype liposomal contrast agent for x-ray imaging of breast cancer: A proof of concept using micro-CT in small animals

Imaging tumor angiogenesis in small animals is extremely challenging due to the size of the tumor vessels. Consequently, both dedicated small animal imaging systems and specialized intravascular contrast agents are required. The goal of this study was to investigate the use of a liposomal contrast agent for high-resolution micro-CT imaging of breast tumors in small animals. A liposomal blood pool agent encapsulating iodine with a concentration of 65.5 mg/ml was used with a Duke Center for In Vivo Microscopy (CIVM) prototype micro-computed tomography (micro-CT) system to image the R3230AC mammary carcinoma implanted in rats. The animals were injected with equivalent volume doses (0.02 ml/kg) of contrast agent. Micro-CT with the liposomal blood pool contrast agent ensured a signal difference between the blood and the muscle higher than 450 HU allowing the visualization of the tumors 3D vascular architecture in exquisite detail at 100-micron resolution. The micro-CT data correlated well with the histological examination of tumor tissue. We also studied the ability to detect vascular enhancement with limited angle based reconstruction, i.e. tomosynthesis. Tumor volumes and their regional vascular percentage were estimated. This imaging approach could be used to better understand tumor angiogenesis and be the basis for evaluating anti-angiogenic therapies.

Authors
Badea, CT; Samei, E; Ghaghada, K; Saunders, R; Yuan, H; Qi, Y; Hedlund, LW; Mukundan, S
MLA Citation
Badea, CT, Samei, E, Ghaghada, K, Saunders, R, Yuan, H, Qi, Y, Hedlund, LW, and Mukundan, S. "Utility of a prototype liposomal contrast agent for x-ray imaging of breast cancer: A proof of concept using micro-CT in small animals." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6913 (2008).
Source
scival
Published In
Proceedings of SPIE
Volume
6913
Publish Date
2008
DOI
10.1117/12.772307

Optimization of dual energy contrast enhanced breast tomosynthesis for improved mammographic lesion detection and diagnosis

Dual-energy contrast-enhanced breast tomosynthesis has been proposed as a technique to improve the detection of early-stage cancer in young, high-risk women. This study focused on optimizing this technique using computer simulations. The computer simulation used analytical calculations to optimize the signal difference to noise ratio (SdNR) of resulting images from such a technique at constant dose. The optimization included the optimal radiographic technique, optimal distribution of dose between the two single-energy projection images, and the optimal weighting factor for the dual energy subtraction. Importantly, the SdNR included both anatomical and quantum noise sources, as dual energy imaging reduces anatomical noise at the expense of increases in quantum noise. Assuming a tungsten anode, the maximum SdNR at constant dose was achieved for a high energy beam at 49 kVp with 92.5 μm copper filtration and a low energy beam at 49 kVp with 95 μm tin filtration. These analytical calculations were followed by Monte Carlo simulations that included the effects of scattered radiation and detector properties. Finally, the feasibility of this technique was tested in a small animal imaging experiment using a novel iodinated liposomal contrast agent. The results illustrated the utility of dual energy imaging and determined the optimal acquisition parameters for this technique. This work was supported in part by grants from the Komen Foundation (PDF55806), the Cancer Research and Prevention Foundation, and the NIH (NCI R21 CA124584-01). CIVM is a NCRR/NCI National Resource under P41-05959/U24-CA092656.

Authors
Saunders, R; Samei, E; Badea, C; Yuan, H; Ghaghada, K; Qi, Y; Hedlund, LW; Mukundan, S
MLA Citation
Saunders, R, Samei, E, Badea, C, Yuan, H, Ghaghada, K, Qi, Y, Hedlund, LW, and Mukundan, S. "Optimization of dual energy contrast enhanced breast tomosynthesis for improved mammographic lesion detection and diagnosis." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6913 (2008).
Source
scival
Published In
Proceedings of SPIE
Volume
6913
Publish Date
2008
DOI
10.1117/12.772042

Towards assessing the diagnostic influence of dose reduction in pediatric CT: A study based on simulated lung nodules

The purpose of this study is to evaluate the effect of reduced tube current, as a surrogate for radiation dose, on lung nodule detection in pediatric chest multi-detector CT (MDCT). Normal chest MDCT images of 13 patients aged 1 to 7 years old were used as templates for this study. The original tube currents were between 70 mA and 180 mA. Using proprietary noise addition software, noise was added to the images to create 13 cases at the lowest common mA (i.e. 70 mA), 13 cases at 35 mA (50% reduction), and 13 cases at 17.5 mA (75% reduction). Three copies of each case were made for a total of 117 series for simulated nodule insertion. A technique for three-dimensional simulation of small lung nodules was developed, validated through an observer study, and used to add nodules to the series. Care was taken to ensure that each of three lung zones (upper, middle, lower) contained 0 or 1 nodule. The series were randomized and the presence of a nodule in each lung zone was rated independently and blindly by three pediatric radiologists on a continuous scale between 0 (definitely absent) and 100 (definitely present). Receiver operating characteristic analysis of the data showed no general significant difference in diagnostic accuracy between the reduced mA values and 70 mA, suggesting a potential for dose reduction with preserved diagnostic quality. To our knowledge, this study is the first controlled, systematic, and task-specific assessment of the influence of dose reduction in pediatric chest CT.

Authors
Xiang, L; Samei, E; DeLong, DM; Jones, RP; Colsher, JG; Frush, DP
MLA Citation
Xiang, L, Samei, E, DeLong, DM, Jones, RP, Colsher, JG, and Frush, DP. "Towards assessing the diagnostic influence of dose reduction in pediatric CT: A study based on simulated lung nodules." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6913 (2008).
Source
scival
Published In
Proceedings of SPIE
Volume
6913
Publish Date
2008
DOI
10.1117/12.772089

Multi-projection correlation imaging as a new diagnostic tool for improved breast cancer detection

Multi-projection imaging technique offers an advantage over single projection imaging techniques in rendering pathology that may be surrounded by a complex cloud of anatomical structures. The process of harnessing the geometrical and statistical dependences between the multiple images available in a multi-projection system to determine the final diagnosis is termed Correlation Imaging (CI). In this study, we are investigating the potential improvement in breast cancer detection via CI. As a key step towards that, the acquisition scheme of CI was first optimized to maximize its diagnostic performance. Toward that end, first a clinically-realistic task was designed and each component of acquisition, namely, the acquisition dose level, the number of projections, and their angular span was systematically changed to determine a specific combination that yielded maximum performance in that task. Finally, the performance of the optimized system was compared with that of standard planar mammography. The results indicated that the performance of CI may potentially be optimized between 15-17 projections spanning an angular arc of 45 o . This optimum performance further improved with increasing dose levels; however, at dose level comparable to mammography, CI provided a factor of 1.1 improvement over mammography. The framework developed in this study to evaluate multi-projections system may be applied to any other multi-projection imaging modality, and by including reconstruction, may be extended to digital breast tomosynthesis and breast computed tomography. © 2008 Springer-Verlag Berlin Heidelberg.

Authors
Chawla, AS; Samei, E; Lo, JY; Mertelmeier, T
MLA Citation
Chawla, AS, Samei, E, Lo, JY, and Mertelmeier, T. "Multi-projection correlation imaging as a new diagnostic tool for improved breast cancer detection." 2008.
Source
scival
Published In
Lecture notes in computer science
Volume
5116 LNCS
Publish Date
2008
Start Page
635
End Page
642
DOI
10.1007/978-3-540-70538-3_88

Knowledge transfer across breast cancer screening modalities: A pilot study using an information-theoretic CADe system for mass detection

We have performed a series of experiments to assess whether a featureless, knowledge-based CADe system that relies on information theoretic principles is capable of transferring knowledge across cases acquired with different imaging modalities. Typical feature-based CADe systems are developed and carefully optimized for a specific imaging modality and platform, namely for screen-film mammograms (SFMs) digitized with a specific digitizer, or for full-field digital mammograms (FFDMs), or for the newly introduced digital breast tomosynthesis (DBT) modality. Multiplatform application of such CADe systems is often limited due to image processing steps that are tailored to the imaging modality and acquisition protocol. It is desirable however to develop CADe systems with the ability to adapt to a dynamically changing environment (i.e., imaging modality) and provide an accurate decision while capitalizing on knowledge acquired at different, yet related environments. Working towards this goal, we present a pilot study using a knowledge-based CADe system for mass detection that uses information theory to assess the similarity between a query and a knowledge case. We evaluate the system's ability to transfer knowledge across three imaging modalities (SFMs digitized with two different digitizers, FFDMs, and DBTs) when performing the detection task. Overall our study showed that although blind translation of the system in a new modality for which no prior knowledge exists results in reduced performance, the system is still able to operate at a very decent level. When the system operated with a knowledge database of mixed cases, its performance was robust and comparable to what observed independently. © 2008 Springer-Verlag Berlin Heidelberg.

Authors
Tourassi, GD; Sharma, AC; Singh, S; Saunders, RS; Lo, JY; Samei, E; Harrawood, BP
MLA Citation
Tourassi, GD, Sharma, AC, Singh, S, Saunders, RS, Lo, JY, Samei, E, and Harrawood, BP. "Knowledge transfer across breast cancer screening modalities: A pilot study using an information-theoretic CADe system for mass detection." 2008.
Source
scival
Published In
Lecture notes in computer science
Volume
5116 LNCS
Publish Date
2008
Start Page
292
End Page
298
DOI
10.1007/978-3-540-70538-3_41

Assessment of low energies and slice depth in the quantification of breast tomosynthesis

This study attempts to assess the quantitative potential of breast tomosynthesis imaging. Tomosynthesis might be a feasible replacement for digital mammography, so it is worthwhile to consider whether it can be quantitative like computed tomography (CT), where the image pixel values are expressed in Hounsfield units. For this investigation, plastic tissue-equivalent breast phantoms with 10 lesions of varying density in the center along with a small density calibration phantom of 5 density-varying lesions were imaged under several different conditions. The measured voxel value for each lesion from a reconstructed slice was linearly rescaled based on the calibration phantom and then plotted against the known glandular fraction of each lesion. It was found that the two different energies and the three different lesion depths all produced linear voxel values versus glandularity relationships. Therefore, tomosynthesis has quantitative potential. However, in order to convert each 3D image's voxel values to values that can be interpreted as a certain glandular fraction, one must consider the x-ray tube energy, slice depth, and many other factors of the imaging system and the breast. © 2008 Springer-Verlag Berlin Heidelberg.

Authors
Shafer, CM; Samei, E; Mertelmeier, T; Saunders, RS; Zerhouni, M; Lo, JY
MLA Citation
Shafer, CM, Samei, E, Mertelmeier, T, Saunders, RS, Zerhouni, M, and Lo, JY. "Assessment of low energies and slice depth in the quantification of breast tomosynthesis." 2008.
Source
scival
Published In
Lecture notes in computer science
Volume
5116 LNCS
Publish Date
2008
Start Page
530
End Page
536
DOI
10.1007/978-3-540-70538-3_74

Optimized acquisition scheme for multi-projection correlation imaging of breast cancer

We are reporting the optimized acquisition scheme of multi-projection breast Correlation Imaging (CI) technique, which was pioneered in our lab at Duke University. CI is similar to tomosynthesis in its image acquisition scheme. However, instead of analyzing the reconstructed images, the projection images are directly analyzed for pathology. Earlier, we presented an optimized data acquisition scheme for CI using mathematical observer model. In this article, we are presenting a Computer Aided Detection (CADe)-based optimization methodology. Towards that end, images from 106 subjects recruited for an ongoing clinical trial for tomosynthesis were employed. For each patient, 25 angular projections of each breast were acquired. Projection images were supplemented with a simulated 3 mm 3D lesion. Each projection was first processed by a traditional CADe algorithm at high sensitivity, followed by a reduction of false positives by combining geometrical correlation information available from the multiple images. Performance of the CI system was determined in terms of free-response receiver operating characteristics (FROC) curves and the area under ROC curves. For optimization, the components of acquisition such as the number of projections, and their angular span were systematically changed to investigate which one of the many possible combinations maximized the sensitivity and specificity. Results indicated that the performance of the CI system may be maximized with 7-11 projections spanning an angular arc of 44.8°, confirming our earlier findings using observer models. These results indicate that an optimized CI system may potentially be an important diagnostic tool for improved breast cancer detection.

Authors
Chawla, AS; Samei, E; Saunders, RS; Lo, JY; Singh, S
MLA Citation
Chawla, AS, Samei, E, Saunders, RS, Lo, JY, and Singh, S. "Optimized acquisition scheme for multi-projection correlation imaging of breast cancer." 2008.
Source
scival
Published In
Proceedings of SPIE
Volume
6915
Publish Date
2008
DOI
10.1117/12.773174

Computer aided detection of breast masses in tomosynthesis reconstructed volumes using information-theoretic similarity measures

The purpose of this project is to study two Computer Aided Detection (CADe) systems for breast masses for digital tomosynthesis using reconstructed slices. This study used eighty human subject cases collected as part of on-going clinical trials at Duke University. Raw projections images were used to identify suspicious regions in the algorithm's high sensitivity, low specificity stage using a Difference of Gaussian filter. The filtered images were thresholded to yield initial CADe hits that were then shifted and added to yield a 3D distribution of suspicious regions. The initial system performance was 95% sensitivity at 10 false positives per breast volume. Two CADe systems were developed. In system A, the central slice located at the centroid depth was used to extract a 256× 256 Regions of Interest (ROI) database centered at the lesion coordinates. For system B, 5 slices centered at the lesion coordinates were summed before the extraction of 256× 256 ROIs. To avoid issues associated with feature extraction, selection, and merging, information theory principles were used to reduce false positives for both the systems resulting in a classifier performance of 0.81 and 0.865 Area Under Curve (AUC) with leave-one-case-out sampling. This resulted in an overall system performance of 87% sensitivity with 6.1 FPs/volume and 85% sensitivity with 3.8 FPs/ volume for systems A and B respectively. This system therefore has the potential to detect breast masses in tomosynthesis data sets.

Authors
Singh, S; Tourassi, GD; Chawla, AS; Saunders, RS; Samei, E; Lo, JY
MLA Citation
Singh, S, Tourassi, GD, Chawla, AS, Saunders, RS, Samei, E, and Lo, JY. "Computer aided detection of breast masses in tomosynthesis reconstructed volumes using information-theoretic similarity measures." 2008.
Source
scival
Published In
Proceedings of SPIE
Volume
6915
Publish Date
2008
DOI
10.1117/12.772978

Toward quantification of breast tomosynthesis imaging

Due to the high prevalence of breast cancer among women, much is being done to detect breast cancer earlier and more accurately. In current clinical practice, the most widely-used mode of breast imaging is mammography. Its main advantages are high sensitivity and low patient dose, although it is still merely a two-dimensional projection of a three-dimensional object. In digital breast tomosynthesis, a three-dimensional image of the breast can be reconstructed, but x-ray projection images of the breast are taken over a limited angular span. However, the breast tomosynthesis device itself is more similar to a digital mammography system and thus is a feasible replacement for mammography. Because of the angular undersampling in breast tomosynthesis, the reconstructed images are not considered quantitative, so a worthwhile question to answer would be whether the voxel values (VVs) in breast tomosynthesis images can be made to indicate tissue type as Hounsfield units do in CT. through some image processing scheme. To investigate this, simple phantoms were imaged consisting of layers of uniform, tissue-equivalent plastic for the background sandwiching a layer of interest containing multiple, small cuboids of tissue-equivalent plastic. After analyzing the reconstructed tomosynthesis images, it was found that the VV in each lesion increases linearly with tissue glandularity. However, for the two different x-ray tube energies and for the two different beam exposure levels tested, the trend-lines all have different slopes and y-intercepts. Thus, breast tomosynthesis has a definite potential to be quantitative, and it would be worthwhile to study other possible dependent parameters (phantom thickness, overall density, etc.) as well as alternative reconstruction algorithms.

Authors
Shafer, CM; Samei, E; Saunders, RS; Zerhouni, M; Lo, JY
MLA Citation
Shafer, CM, Samei, E, Saunders, RS, Zerhouni, M, and Lo, JY. "Toward quantification of breast tomosynthesis imaging." 2008.
Source
scival
Published In
Proceedings of SPIE
Volume
6913
Publish Date
2008
DOI
10.1117/12.772753

Breast mass detection under increased ambient lighting

Under typical dark conditions found in mammography reading rooms, a reader's pupils will contract and dilate as the visual focus moves between the high luminance display and the darker background wall, potentially resulting in visual fatigue and degraded diagnostic performance. A controlled increase of ambient lighting can, however, minimize this luminance discrepancy, potentially reducing pupillary action while improving reader comfort and detection ability. A psychophysical study was conducted to determine the effect of a controlled ambient lighting increase on observer detection of subtle masses within mammograms viewed on a DICOM-calibrated medical-grade LCD. Four mammographers read 86 mammograms (43 normal and 43 with cancerous masses) under a dark room condition (1 lux) and an elevated room illuminance level (50 lux). Results show generally constant or decreased average selection times and decreased average observer performance under elevated illuminance. Differences, however, were not statistically significant, and of the same magnitude as interobserver variability. © 2008 Springer-Verlag Berlin Heidelberg.

Authors
Pollard, BJ; Chawla, AS; Hashimoto, N; Samei, E
MLA Citation
Pollard, BJ, Chawla, AS, Hashimoto, N, and Samei, E. "Breast mass detection under increased ambient lighting." Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) 5116 LNCS (2008): 243-248.
Source
scival
Published In
Lecture notes in computer science
Volume
5116 LNCS
Publish Date
2008
Start Page
243
End Page
248
DOI
10.1007/978-3-540-70538-3_34

Reconstruction filters and contrast detail curves in CT

In this study, we investigated the effect of CT reconstruction filters in abdominal CT images of a male anthropomorphic phantom. A GE Light Speed CT 4-slice scanner was used to scan the abdomen of an adult Rando phantom. Cross sectional images of the phantom were reconstructed using four reconstruction filters: (1) soft tissue with the lowest noise; (2) detail (relative noise 1.7); (3) bone (relative noise 4.5); and (4) edge (relative noise 7.7). A two Alternate Forced Choice (AFC) experimental paradigm was used to estimate the intensity needed to achieve 92% correct (i.e., I92%) Four observers measured detection performance for five lesions with size ranging from 2.5 to 12.5 mm for each of these four reconstruction filters. Contrast detail curves obtained in images of an anthropomorphic phantom were not straight lines, but best fitted to a second order polynomial. Results from four readers show similar trends with modest inter-observer differences with the measured coefficient of variation of the absolute performance levels of ∼22%. All reconstruction filters had similar shaped contrast detail curves except for smallest details where the frequency response of filters differed most significantly. Increasing the noise level always reduced detection performance, and a doubling of image noise resulted in an average drop in detection performance of ∼20%. The key findings of this study are that (a) the Rose model can provide reasonable predictions as to how changes in lesion size affect observer detection; (b) the shape of CT contrast detail curves is affected only very slightly with reconstruction filter; (c) changes in reconstruction filter noise can predict qualitative changes in observer detection performance, but are poor direct predictors of the quantitative changes of imaging performance.

Authors
Huda, W; Ogden, KM; Samei, E; Scalzetti, EM; Lavallee, RL; Roskopf, ML; Groat, GE
MLA Citation
Huda, W, Ogden, KM, Samei, E, Scalzetti, EM, Lavallee, RL, Roskopf, ML, and Groat, GE. "Reconstruction filters and contrast detail curves in CT." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6917 (2008).
Source
scival
Published In
Proceedings of SPIE
Volume
6917
Publish Date
2008
DOI
10.1117/12.770530

Mass detection on mammograms: Signal variations and performance changes for human and model observers

We studied the influence of signal variability on human and model observer performances for a detection task with mammographic backgrounds and computer generated clustered lumpy backgrounds (CLB). We used synthetic yet realistic masses and backgrounds that have been validated by radiologists during previous studies, ensuring conditions close to the clinical situation. Four trained non-physician observers participated in two-alternative forced-choice (2-AFC) experiments. They were asked to detect synthetic masses superimposed on real mammographic backgrounds or CLB. Separate experiments were conducted with sets of benign and malignant masses. Results under the signal-known-exactly (SKE) paradigm were compared with signal-known-statistically (SKS) experiments. In the latter case, the signal was chosen randomly for each of the 1,400 2-AFC trials (image pairs) among a set of 50 masses with similar dimensions, and the observers did not know which signal was present. Human observers' results were then compared with model observers (channelized Hotelling with Difference-of-Gaussian and Gabor channels) in the same experimental conditions. Results show that the performance of the human observers does not differ significantly when benign masses are superimposed on real images or on CLB with locally matched gray level mean and standard deviation. For both benign and malignant masses, the performance does not differ significantly between SKE and SKS experiments, when the signals' dimensions do not vary throughout the experiment. However, there is a performance drop when the SKS signals' dimensions vary from 5.5 to 9.5 mm in the same experiment. Noise level in the model observers can be adjusted to reproduce human observers' proportion of correct answers in the 2-AFC task within 5% accuracy for most conditions.

Authors
Castella, C; Kinkel, K; Eckstein, MP; Abbey, CK; Verdun, FR; Saunders, RS; Samei, E; Bochud, FO
MLA Citation
Castella, C, Kinkel, K, Eckstein, MP, Abbey, CK, Verdun, FR, Saunders, RS, Samei, E, and Bochud, FO. "Mass detection on mammograms: Signal variations and performance changes for human and model observers." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6917 (2008).
Source
scival
Published In
Proceedings of SPIE
Volume
6917
Publish Date
2008
DOI
10.1117/12.769415

Inter-reader variability in Alternate Forced Choice studies

In this study, we investigated differences in detection performance for twelve observers who each generated a CT contrast detail curve. An anthropomorphic newborn phantom's abdomen was imaged using a GE Light Speed CT scanner (4-slice). Alternate Forced Choice (AFC) experiments were performed with lesions sizes ranging from 2.5 to 12.5 mm to determine the intensity needed to achieve 92% correct (I92%). Following training, twelve readers consisting of (2 technologists, 4 college students, 4 medical students, and 2 radiology residents) generated a single contrast detail curve. Eight readers produced approximately linear contrast detail curves while the remaining four readers required a second order polynomial fit because of reduced performance when detecting the largest (i.e., 12.5 mm) lesion. For the three smallest lesions, the coefficient of variation between the twelve readers was ∼12%, which increases with increasing lesion size to ∼23% for 12.5 mm lesion size. The ratio of the maximum I92%.to minimum I92% values was ∼1.6 for the smallest lesions, which increased to a factor of ∼2.1 for the 12.5 mm lesion. Our results show that minimizing inter-reader variability in our AFC experiments could be achieved by eliminating the largest lesion that cause detection problems in one third of observers. The combined experimental data showed that the slope of the contrast detail curve was -0.42, lower than the value of -1.0 predicted by the Rose model, suggesting that the noise texture in CT associated with both quantum mottle and anatomic structure is an important factor affecting detection of these lesions.

Authors
Huda, W; Ogden, KM; Samei, E; Scalzetti, EM; Lavallee, RL; Roskopf, ML
MLA Citation
Huda, W, Ogden, KM, Samei, E, Scalzetti, EM, Lavallee, RL, and Roskopf, ML. "Inter-reader variability in Alternate Forced Choice studies." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6917 (2008).
Source
scival
Published In
Proceedings of SPIE
Volume
6917
Publish Date
2008
DOI
10.1117/12.770618

The effect of increased ambient lighting on detection accuracy in uniform and anatomical backgrounds

Under typical dark conditions found in reading rooms, a reader's pupils will contract and dilate as the visual focus intermittently shifts between the high luminance monitor and the darker background wall, resulting in increased visual fatigue and the degradation of diagnostic performance. A controlled increase of ambient lighting may, however, minimize these visual adjustments and potentially improve reader comfort and accuracy. This paper details results from two psychophysical studies designed to determine the effect of a controlled ambient lighting increase on observer detection of subtle objects and lesions viewed on a DICOM-calibrated medical-grade LCD. The first study examined the effect of increased ambient lighting on detection of subtle objects embedded within a uniform background, while the second study examined observer detection performance of subtle cancerous lesions in mammograms and chest radiographs. In both studies, observers were presented with images under a dark room condition (1 lux) and an increased room illuminance level (50 lux) for which the luminance level of the diffusely reflected light from the background wall was approximately equal to that of the displayed image. The display was calibrated to an effective luminance ratio of 409 for both lighting conditions. Observer detection performance under each room illuminance condition was then compared. Identification of subtle objects embedded within the uniform background improved from 59% to 67%, while detection time decreased slightly with additional illuminance. An ROC analysis of the anatomical image results revealed that observer AUC values remained constant while detection time decreased under increased illuminance. The results provide evidence that an ambient lighting increase may be possible without compromising diagnostic efficacy.

Authors
Pollard, BJ; Chawla, AS; Hashimoto, N; Samei, E
MLA Citation
Pollard, BJ, Chawla, AS, Hashimoto, N, and Samei, E. "The effect of increased ambient lighting on detection accuracy in uniform and anatomical backgrounds." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6919 (2008).
Source
scival
Published In
Proceedings of SPIE
Volume
6919
Publish Date
2008
DOI
10.1117/12.772932

Toward quantification of breast tomosynthesis imaging

Authors
Shafer, CM; Samei, E; Saunders, RS; Zerhouni, M; Lo, JY
MLA Citation
Shafer, CM, Samei, E, Saunders, RS, Zerhouni, M, and Lo, JY. "Toward quantification of breast tomosynthesis imaging." MEDICAL IMAGING 2008: PHYSICS OF MEDICAL IMAGING, PTS 1-3 6913 (2008).
Source
wos-lite
Published In
Proceedings of SPIE - The International Society for Optical Engineering
Volume
6913
Publish Date
2008
DOI
10.1117/12.772753

Does image quality matter? Impact of resolution and noise on mammographic task performance.

The purpose of this study was to examine the effects of different resolution and noise levels on task performance in digital mammography. This study created an image set with images at three different resolution levels, corresponding to three digital display devices, and three different noise levels, with noise magnitudes similar to full clinical dose, half clinical dose, and quarter clinical dose. The images were read by five experienced breast imaging radiologists. The data were then analyzed to compute two accuracy statistics (overall classification accuracy and lesion detection accuracy) and performance at four diagnostic tasks (detection of microcalcifications, benign masses, malignant masses, and discrimination of benign and malignant masses). Human observer results showed decreasing display resolution had little effect on overall classification accuracy and individual diagnostic task performance, but increasing noise caused overall classification accuracy to decrease by a statistically significant 21% as the breast dose went to one quarter of its normal clinical value. The noise effects were most prominent for the tasks of microcalcification detection and mass discrimination. When the noise changed from full clinical dose to quarter clinical dose, the microcalcification detection performance fell from 89% to 67% and the mass discrimination performance decreased from 93% to 79%, while malignant mass detection performance remained relatively constant with values of 88% and 84%, respectively. As a secondary aim, the image set was also analyzed by two observer models to examine whether their performance was similar to humans. Observer models differed from human observers and each other in their sensitivity to resolution degradation and noise. The primary conclusions of this study suggest that quantum noise appears to be the dominant image quality factor in digital mammography, affecting radiologist performance much more profoundly than display resolution.

Authors
Saunders, RS; Baker, JA; Delong, DM; Johnson, JP; Samei, E
MLA Citation
Saunders, RS, Baker, JA, Delong, DM, Johnson, JP, and Samei, E. "Does image quality matter? Impact of resolution and noise on mammographic task performance." Med Phys 34.10 (October 2007): 3971-3981.
PMID
17985642
Source
pubmed
Published In
Medical physics
Volume
34
Issue
10
Publish Date
2007
Start Page
3971
End Page
3981
DOI
10.1118/1.2776253

Effect of dose reduction on the detection of mammographic lesions: a mathematical observer model analysis.

The effect of reduction in dose levels normally used in mammographic screening procedures on the detection of breast lesions were analyzed. Four types of breast lesions were simulated and inserted into clinically-acquired digital mammograms. Dose reduction by 50% and 75% of the original clinically-relevant exposure levels were simulated by adding corresponding simulated noise into the original mammograms. The mammograms were converted into luminance values corresponding to those displayed on a clinical soft-copy display station and subsequently analyzed by Laguerre-Gauss and Gabor channelized Hotelling observer models for differences in detectability performance with reduction in radiation dose. Performance was measured under a signal known exactly but variable detection task paradigm in terms of receiver operating characteristics (ROC) curves and area under the ROC curves. The results suggested that luminance mapping of digital mammograms affects performance of model observers. Reduction in dose levels by 50% lowered the detectability of masses with borderline statistical significance. Dose reduction did not have a statistically significant effect on detection of microcalcifications. The model results indicate that there is room for optimization of dose level in mammographic screening procedures.

Authors
Chawla, AS; Samei, E; Saunders, R; Abbey, C; Delong, D
MLA Citation
Chawla, AS, Samei, E, Saunders, R, Abbey, C, and Delong, D. "Effect of dose reduction on the detection of mammographic lesions: a mathematical observer model analysis." Med Phys 34.8 (August 2007): 3385-3398.
PMID
17879801
Source
pubmed
Published In
Medical physics
Volume
34
Issue
8
Publish Date
2007
Start Page
3385
End Page
3398
DOI
10.1118/1.2756607

Assessment of detective quantum efficiency: intercomparison of a recently introduced international standard with prior methods.

PURPOSE: To prospectively evaluate the recently introduced international standard method for measurement of the detective quantum efficiency (DQE) of digital radiography systems, in comparison with representative prior methods. MATERIALS AND METHODS: A recently introduced international standard method (International Electrotechnical Commission [IEC] 62220-1, 2003) for DQE measurement and two previously described DQE evaluation methods were considered. In addition to an overall comparison, evaluations of the following method factors were performed: beam quality, beam-limiting devices (apertures or collimators), noise power spectrum (NPS) analysis algorithms and parameters (area, region of interest size, background detrending), and modulation transfer function (MTF) test devices and methods. RESULTS: Overall, at low to middle frequencies, the IEC method yielded DQE estimates that were 3.3% and 6.5% lower than the values yielded by the two previous methods. Averaged over the frequency range of 1.5-2.5 mm(-1), the DQE estimate derived by using the IEC method was 7.1% lower and 12.4% higher than the estimates derived by using the other two methods. Results obtained with the two previous DQE evaluation methods agreed well (within 2.0%) in the low- to middle-frequency range but diverged by up to 10% at higher frequencies. When the DQE method factors were evaluated separately, the largest percentage deviations in DQE were associated with (in order of decreasing influence) the MTF analysis method ( approximately 11%), the beam limitation (about 7%-10%), the beam quality ( approximately 9%), and the NPS analysis method ( approximately 3%). CONCLUSION: Comparison of DQE estimates obtained by using the recently introduced international standard technique with those obtained by using prior methods revealed that the overall measurement method can affect the DQE estimate by as much as 12%. Findings further suggest that both beam limitation achieved by means of internal collimation (rather than external apertures) and use of a radio-opaque edge MTF device yield a more accurate estimation of the DQE.

Authors
Ranger, NT; Samei, E; Dobbins, JT; Ravin, CE
MLA Citation
Ranger, NT, Samei, E, Dobbins, JT, and Ravin, CE. "Assessment of detective quantum efficiency: intercomparison of a recently introduced international standard with prior methods." Radiology 243.3 (June 2007): 785-795.
PMID
17517933
Source
pubmed
Published In
Radiology
Volume
243
Issue
3
Publish Date
2007
Start Page
785
End Page
795
DOI
10.1148/radiol.2433060485

New developments in digital breast tomosynthesis

Authors
Lo, JY; Singh, S; III, DJT; Samei, E
MLA Citation
Lo, JY, Singh, S, III, DJT, and Samei, E. "New developments in digital breast tomosynthesis." June 2007.
Source
wos-lite
Published In
Medical physics
Volume
34
Issue
6
Publish Date
2007
Start Page
2518
End Page
2518
DOI
10.1118/1.2761222

Image quality measurement workshop

Authors
Samei, E
MLA Citation
Samei, E. "Image quality measurement workshop." June 2007.
Source
wos-lite
Published In
Medical physics
Volume
34
Issue
6
Publish Date
2007
Start Page
2570
End Page
2571
DOI
10.1118/1.2761436

Optimizing mammography image quality and dose: X-ray spectrum and exposure parameter selection

Authors
Williams, M; Raghunathan, P; Seibert, JA; Kwan, A; Lo, J; Samei, E; Ranger, N; Fajardo, L; McGruder, A; Maxwell, S; Maidment, A; Yaffe, M; Bloomquist, A; Mawdsley, G
MLA Citation
Williams, M, Raghunathan, P, Seibert, JA, Kwan, A, Lo, J, Samei, E, Ranger, N, Fajardo, L, McGruder, A, Maxwell, S, Maidment, A, Yaffe, M, Bloomquist, A, and Mawdsley, G. "Optimizing mammography image quality and dose: X-ray spectrum and exposure parameter selection." June 2007.
Source
wos-lite
Published In
Medical physics
Volume
34
Issue
6
Publish Date
2007
Start Page
2540
End Page
2541
DOI
10.1118/1.2761315

An evaluation of noise in radiotracer emission imaging using flat-panel detectors

Authors
Bowsher, J; Yin, F; Chawla, A; Greer, K; Song, H; Samei, E; Willett, C
MLA Citation
Bowsher, J, Yin, F, Chawla, A, Greer, K, Song, H, Samei, E, and Willett, C. "An evaluation of noise in radiotracer emission imaging using flat-panel detectors." June 2007.
Source
wos-lite
Published In
Medical physics
Volume
34
Issue
6
Publish Date
2007
Start Page
2636
End Page
2636
DOI
10.1118/1.2761701

Evaluation of a noise addition software for simulating low dose MDCT images

Authors
Li, X; Samei, E; Thomas, A; Colsher, J; Toth, T; Frush, D
MLA Citation
Li, X, Samei, E, Thomas, A, Colsher, J, Toth, T, and Frush, D. "Evaluation of a noise addition software for simulating low dose MDCT images." June 2007.
Source
wos-lite
Published In
Medical physics
Volume
34
Issue
6
Publish Date
2007
Start Page
2344
End Page
2344
DOI
10.1118/1.2760405

Digital mammography: comparative performance of color LCD and monochrome CRT displays.

RATIONALE AND OBJECTIVES: To evaluate the comparative performance of high-fidelity liquid crystal display (LCD) and cathode ray tube (CRT) devices for mammography applications, and to assess the impact of LCD viewing angle on detection accuracy. MATERIALS AND METHODS: Ninety 1 k x 1 k images were selected from a database of digital mammograms: 30 without any abnormality present, 30 with subtle masses, and 30 with subtle microcalcifications. The images were used with waived informed consent, Health Insurance Portability and Accountability Act compliance, and Institutional Review Board approval. With postprocessing presentation identical to those of the commercial mammography system used, 1 k x 1 k sections of images were viewed on a monochrome CRT and a color LCD in native grayscale, and with a grayscale representative of images viewed from a 30 degrees or 50 degrees off-normal viewing angle. Randomized images were independently scored by four experienced breast radiologists for the presence of lesions using a 0-100 grading scale. To compare diagnostic performance of the display modes, observer scores were analyzed using receiver operating characteristic (ROC) and analysis of variance. RESULTS: For masses and microcalcifications, the detection rate in terms of the area under the ROC curve (A(z)) showed a 2% increase and a 4% decrease from CRT to LCD, respectively. However, differences were not statistically significant (P > .05). The viewing angle data showed better microcalcification detection but lower mass detection at 30 degrees viewing orientation. The overall results varied notably from observer to observer yielding no statistically discernible trends across all observers, suggesting that within the 0-50 degrees viewing angle range and in a controlled observer experiment, the variation in the contrast response of the LCD has little or no impact on the detection of mammographic lesions. CONCLUSIONS: Although CRTs and LCDs differ in terms of angular response, resolution, noise, and color, these characteristics seem to have little influence on the detection of mammographic lesions. The results suggest comparable performance in clinical applications of the two devices.

Authors
Samei, E; Poolla, A; Ulissey, MJ; Lewin, JM
MLA Citation
Samei, E, Poolla, A, Ulissey, MJ, and Lewin, JM. "Digital mammography: comparative performance of color LCD and monochrome CRT displays." Acad Radiol 14.5 (May 2007): 539-546.
PMID
17434067
Source
pubmed
Published In
Academic Radiology
Volume
14
Issue
5
Publish Date
2007
Start Page
539
End Page
546
DOI
10.1016/j.acra.2007.01.022

Digital mammography: effects of reduced radiation dose on diagnostic performance.

PURPOSE: To experimentally determine the relationship between radiation dose and observer accuracy in the detection and discrimination of simulated lesions for digital mammography. MATERIALS AND METHODS: This HIPAA-compliant study received institutional review board approval; the informed consent requirement was waived. Three hundred normal craniocaudal images were selected from an existing database of digital mammograms. Simulated mammographic lesions that mimicked benign and malignant masses and clusters of microcalcifications (3.3-7.4 cm in diameter) were then superimposed on images. Images were rendered without and with added radiographic noise to simulate effects of reducing the radiation dose to one half and one quarter of the clinical dose. Images were read by five experienced breast imaging radiologists. Results were analyzed to determine effects of reduced dose on overall interpretation accuracy, detection of microcalcifications and masses, discrimination between benign and malignant masses, and interpretation time. RESULTS: Overall accuracy decreased from 0.83 with full dose to 0.78 and 0.62 with half and quarter doses, respectively. The decrease associated with transition from full dose to quarter dose was significant (P < .01), primarily because of an effect on detection of microcalcifications (P < .01) and discrimination of masses (P < .05). The level of dose reduction did not significantly affect detection of malignant masses (P > .5). However, reduced dose resulted in an increased mean interpretation time per image by 28% (P < .0001). CONCLUSION: These findings suggest that dose reduction in digital mammography has a measurable but modest effect on diagnostic accuracy. The small magnitude of the effect in response to the drastic reduction of dose suggests potential for modest dose reductions in digital mammography.

Authors
Samei, E; Saunders, RS; Baker, JA; Delong, DM
MLA Citation
Samei, E, Saunders, RS, Baker, JA, and Delong, DM. "Digital mammography: effects of reduced radiation dose on diagnostic performance." Radiology 243.2 (May 2007): 396-404.
PMID
17356178
Source
pubmed
Published In
Radiology
Volume
243
Issue
2
Publish Date
2007
Start Page
396
End Page
404
DOI
10.1148/radiol.2432061065

Multiprojection correlation imaging for improved detection of pulmonary nodules.

OBJECTIVE: The purpose of this study was the development and preliminary evaluation of multiprojection correlation imaging with 3D computer-aided detection (CAD) on chest radiographs for cost- and dose-effective improvement of early detection of pulmonary nodules. SUBJECTS AND METHODS: Digital chest radiographs of 10 configurations of a chest phantom and of seven human subjects were acquired in multiple angular projections with an acquisition time of 11 seconds (single breath-hold) and total exposure comparable with that of a posteroanterior chest radiograph. An initial 2D CAD algorithm with two difference-of-gaussians filters and multilevel thresholds was developed with an independent database of 44 single-view chest radiographs with confirmed lesions. This 2D CAD algorithm was used on each projection image to find likely suspect nodules. The CAD outputs were reconstructed in 3D, reinforcing signals associated with true nodules while simultaneously decreasing false-positive findings produced by overlapping anatomic features. The performance of correlation imaging was tested on two to 15 projection images. RESULTS: Optimum performance of correlation imaging was attained when nine projection images were used. Compared with conventional, single-view CAD, correlation imaging decreased as much as 79% the frequency of false-positive findings in phantom cases at a sensitivity level of 65%. The corresponding reduction in false-positive findings in the cases of human subjects was 78%. CONCLUSION: Although limited by a relatively simple CAD implementation and a small number of cases, the findings suggest that correlation imaging performs substantially better than single-view CAD and may greatly enhance identification of subtle solitary pulmonary nodules on chest radiographs.

Authors
Samei, E; Stebbins, SA; Dobbins, JT; McAdams, HP; Lo, JY
MLA Citation
Samei, E, Stebbins, SA, Dobbins, JT, McAdams, HP, and Lo, JY. "Multiprojection correlation imaging for improved detection of pulmonary nodules." AJR Am J Roentgenol 188.5 (May 2007): 1239-1245.
PMID
17449766
Source
pubmed
Published In
AJR. American journal of roentgenology
Volume
188
Issue
5
Publish Date
2007
Start Page
1239
End Page
1245
DOI
10.2214/AJR.06.0843

Tomographic digital subtraction angiography for lung perfusion estimation in rodents.

In vivo measurements of perfusion present a challenge to existing small animal imaging techniques such as magnetic resonance microscopy, micro computed tomography, micro positron emission tomography, and microSPECT, due to combined requirements for high spatial and temporal resolution. We demonstrate the use of tomographic digital subtraction angiography (TDSA) for estimation of perfusion in small animals. TDSA augments conventional digital subtraction angiography (DSA) by providing three-dimensional spatial information using tomosynthesis algorithms. TDSA is based on the novel paradigm that the same time density curves can be reproduced in a number of consecutive injections of microL volumes of contrast at a series of different angles of rotation. The capabilities of TDSA are established in studies on lung perfusion in rats. Using an imaging system developed in-house, we acquired data for four-dimensional (4D) imaging with temporal resolution of 140 ms, in-plane spatial resolution of 100 microm, and slice thickness on the order of millimeters. Based on a structured experimental approach, we optimized TDSA imaging providing a good trade-off between slice thickness, the number of injections, contrast to noise, and immunity to artifacts. Both DSA and TDSA images were used to create parametric maps of perfusion. TDSA imaging has potential application in a number of areas where functional perfusion measurements in 4D can provide valuable insight into animal models of disease and response to therapeutics.

Authors
Badea, CT; Hedlund, LW; De Lin, M; Mackel, JSB; Samei, E; Johnson, GA
MLA Citation
Badea, CT, Hedlund, LW, De Lin, M, Mackel, JSB, Samei, E, and Johnson, GA. "Tomographic digital subtraction angiography for lung perfusion estimation in rodents." Med Phys 34.5 (May 2007): 1546-1555.
PMID
17555236
Source
pubmed
Published In
Medical physics
Volume
34
Issue
5
Publish Date
2007
Start Page
1546
End Page
1555
DOI
10.1118/1.2717384

Dose dependence of mass and microcalcification detection in digital mammography: free response human observer studies.

The purpose of this study was to evaluate the effect of dose reduction in digital mammography on the detection of two lesion types-malignant masses and clusters of microcalcifications. Two free-response observer studies were performed-one for each lesion type. Ninety screening images were retrospectively selected; each image was originally acquired under automatic exposure conditions, corresponding to an average glandular dose of 1.3 mGy for a standard breast (50 mm compressed breast thickness with 50% glandularity). For each study, one to three simulated lesions were added to each of 40 images (abnormals) while 50 were kept without lesions (normals). Two levels of simulated system noise were added to the images yielding two new image sets, corresponding to simulated dose levels of 50% and 30% of the original images (100%). The manufacturer's standard display processing was subsequently applied to all images. Four radiologists experienced in mammography evaluated the images by searching for lesions and marking and assigning confidence levels to suspicious regions. The search data were analyzed using jackknife free-response (JA-FROC) methodology. For the detection of masses, the mean figure-of-merit (FOM) averaged over all readers was 0.74, 0.71, and 0.68 corresponding to dose levels of 100%, 50%, and 30%, respectively. These values were not statistically different from each other (F= 1.67, p=0.19) but showed a decreasing trend. In contrast, in the microcalcification study the mean FOM was 0.93, 0.67, and 0.38 for the same dose levels and these values were all significantly different from each other (F = 109.84, p < 0.0001). The results indicate that lowering the present dose level by a factor of two compromised the detection of microcalcifications but had a weaker effect on mass detection.

Authors
Ruschin, M; Timberg, P; Båth, M; Hemdal, B; Svahn, T; Saunders, RS; Samei, E; Andersson, I; Mattsson, S; Chakrabort, DP; Tingber, A
MLA Citation
Ruschin, M, Timberg, P, Båth, M, Hemdal, B, Svahn, T, Saunders, RS, Samei, E, Andersson, I, Mattsson, S, Chakrabort, DP, and Tingber, A. "Dose dependence of mass and microcalcification detection in digital mammography: free response human observer studies." Med Phys 34.2 (February 2007): 400-407.
PMID
17388156
Source
pubmed
Published In
Medical physics
Volume
34
Issue
2
Publish Date
2007
Start Page
400
End Page
407
DOI
10.1118/1.2405324

Ambient illumination revisited: a new adaptation-based approach for optimizing medical imaging reading environments.

Ambient lighting in soft-copy reading rooms is currently kept at low values to preserve contrast rendition in the dark regions of a medical image. Low illuminance levels, however, create inadequate viewing conditions and may also cause eye strain. This eye strain may be potentially attributed to notable variations in the luminance adaptation state of the reader's eyes when moving the gaze intermittently between the brighter display and darker surrounding surfaces. This paper presents a methodology to minimize this variation and optimize the lighting conditions of reading rooms by exploiting the properties of liquid crystal displays (LCDs) with low diffuse reflection coefficients and high luminance ratio. First, a computational model was developed to determine a global luminance adaptation value, Ladp, when viewing a medical image on display. The model is based on the diameter of the pupil size, which depends on the luminance of the observed object. Second, this value was compared with the luminance reflected off surrounding surfaces, Ls, under various conditions of room illuminance, E, different values of diffuse reflection coefficients of surrounding surfaces, Rs, and calibration settings of a typical LCD. The results suggest that for typical luminance settings of current LCDs, it is possible to raise ambient illumination to minimize differences in eye adaptation, potentially reducing visual fatigue while also complying with the TG18 specifications for controlled contrast rendition. Specifically, room illumination in the 75-150 lux range and surface diffuse reflection coefficients in the practical range of 0.13-0.22 sr(-1) provide an ideal setup for typical LCDs. Future LCDs with lower diffuse reflectivity and with higher inherent luminance ratios can provide further improvement of ergonomic viewing conditions in reading rooms.

Authors
Chawla, AS; Samei, E
MLA Citation
Chawla, AS, and Samei, E. "Ambient illumination revisited: a new adaptation-based approach for optimizing medical imaging reading environments." Med Phys 34.1 (January 2007): 81-90.
PMID
17278493
Source
pubmed
Published In
Medical physics
Volume
34
Issue
1
Publish Date
2007
Start Page
81
End Page
90
DOI
10.1118/1.2402583

Effect of increased ambient lighting on detectability - A psychophysical study

Last year in this conference, we presented a theoretical analysis of how ambient lighting in dark reading rooms could be moderately increased without compromising the interpretation of images displayed on LCDs.' Based on that analysis, in this paper we present results of two psychophysical experiments which were designed to verify those theoretical predictions. The first experiment was designed to test how an increase in ambient lighting affects the detection of subtle objects at different luminance levels, particularly at lower luminance levels. Towards that end, images of targets consisting of low-contrast objects were shown to seven observers, first under a dark room illumination condition of 1 lux and then under a higher room illumination condition of 50 lux. The targets had three base luminance values of 1, 12 and 35 cd/m 2 and were embedded in a uniform background. The uniform background was set to 12 cd/m 2 which enabled fixing L adp, the visual adaptation luminance value when looking at the display, to 12 cd/m 2. This value also matched the luminance value of about 12 cd/m 2 reflected off the wall surrounding the LCD at the higher ambient lighting condition. The task of the observers was to detect and classify the displayed objects under the two room lighting conditions. The results indicated that the detection rate in dark area (base luminance of 1 cd/m 2) increased by 15% when the ambient illumination is increased from 1 to 50 lux. The increase was not conclusive for targets embedded in higher luminance regions, but there was no evidence to the contrary either. The second experiment was designed to investigate the adaptation luminance value of the eye when viewing typical mammograms. It was found that, for a typical display luminance calibration, this value might lie between 12 and 20 cd/m 2. Findings from the two experiments provide justification for a controlled increase of ambient lighting to improve ergonomic viewing conditions in darkly lit reading rooms while potentially improving diagnostic performance.

Authors
Chawla, AS; Pollard, B; Samei, E; Hashimoto, N
MLA Citation
Chawla, AS, Pollard, B, Samei, E, and Hashimoto, N. "Effect of increased ambient lighting on detectability - A psychophysical study." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6516 (2007).
Source
scival
Published In
Proceedings of SPIE
Volume
6516
Publish Date
2007
DOI
10.1117/12.713559

A mathematical model approach towards combining information from multiple image projections of the same patient

The purpose of this study was to, i) use a mathematical observer model to combine information obtained from multiple angular projections of the same breast to determine the overall detectability of a simulated lesion in a multi-projection breast imaging system and, ii) determine the optimum acquisition parameters of such a system. Multi-projection imaging is similar to tomosynthesis, except that the raw projection images are directly analyzed instead of reconstructing those images, thereby avoiding reconstruction artifacts. 25 angular projections of each breast from 82 human subjects in our tomosynthesis clinical trials were supplemented with projections from a simulated 3 mm 3D lesion. The lesion was assumed to be embedded in the compressed breast at a distance of 3 cm from the detector. The contrast of the lesion was determined taking into account the energy spectrum of the x-ray beam, properties of the digital detector, scatter fraction, and compressed breast thickness. A linear Hotelling observer with Laguerre-Gauss channels (LG CHO) was applied to each image. Detectability was analyzed in terms of ROC curves and the area under ROC curves (AUC). Three different methods were used to integrate ROCs from multiple (correlated) views to obtain one combined ROC as an overall metric of detectability. Specifically, 1) ROCs from different projections were simply averaged; 2) the test statistics from different projections were averaged; and 3) a Bayesian decision fusion rule was used. Finally, the number of angular projections, angular span and the acquisition dose level were optimized for highest AUC of the combined ROC as a parameter to maximize the performance of the system. It was found that the Bayesian decision fusion technique performs better than the other two techniques and likely offers the best approximation of the diagnostic process. Furthermore, if the total dose level is held constant at 1/25 th of the standard dual-view mammographic screening dose, the highest detectability performance is observed when considering only two projections spread along an angular span of 11.4°.

Authors
Chawla, AS; Samei, E; Abbey, C
MLA Citation
Chawla, AS, Samei, E, and Abbey, C. "A mathematical model approach towards combining information from multiple image projections of the same patient." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6510.PART 1 (2007).
Source
scival
Published In
Proceedings of SPIE
Volume
6510
Issue
PART 1
Publish Date
2007
DOI
10.1117/12.713651

Methodology of NEQ (f) analysis for optimization and comparison of digital breast tomosynthesis acquisition techniques and reconstruction algorithms

As a new three-dimensional imaging technique, digital breast tomosynthesis allows the reconstruction of an arbitrary set of planes in the breast from a limited-angle series of projection images. Though several tomosynthesis algorithms have been proposed, no complete optimization and comparison of different tomosynthesis acquisition techniques for available methods has been conducted as of yet. This paper represents a methodology of noise-equivalent quanta NEQ (f) analysis to optimize and compare the efficacy of tomosynthesis algorithms and imaging acquisition techniques for digital breast tomosynthesis. It combines the modulation transfer function (MTF) of system signal performance and the noise power spectrum (NPS) of noise characteristics. It enables one to evaluate the performance of different acquisition parameters and algorithms for comparison and optimization purposes. An example of this methodology was evaluated on a selenium-based direct-conversion flat-panel Siemens Mammomat Novation prototype system. An edge method was used to measure the presampled MTF of the detector. The MTF associated with the reconstruction algorithm and specific acquisition technique was investigated by calculating the Fourier Transform of simulated impulse responses. Flat field tomosynthesis projection sequences were acquired and then reconstructed. A mean-subtracted NPS on the reconstructed plane was studied to remove fixed pattern noise. An example of the application of this methodology was illustrated in this paper using a point-by-point Back Projection correction (BP) reconstruction algorithm and an acquisition technique of 25 projections with 25 degrees total angular tube movement.

Authors
Chen, Y; Lo, JY; Ranger, NT; Samei, E; III, JTD
MLA Citation
Chen, Y, Lo, JY, Ranger, NT, Samei, E, and III, JTD. "Methodology of NEQ (f) analysis for optimization and comparison of digital breast tomosynthesis acquisition techniques and reconstruction algorithms." 2007.
Source
scival
Published In
Proceedings of SPIE
Volume
6510
Issue
PART 1
Publish Date
2007
DOI
10.1117/12.713737

Experimental benchmarking of a Monte Carlo dose simulation code for pediatric CT

In recent years, there has been a desire to reduce CT radiation dose to children because of their susceptibility and prolonged risk for cancer induction. Concerns arise, however, as to the impact of dose reduction on image quality and thus potentially on diagnostic accuracy. To study the dose and image quality relationship, we are developing a simulation code to calculate organ dose in pediatric CT patients. To benchmark this code, a cylindrical phantom was built to represent a pediatric torso, which allows measurements of dose distributions from its center to its periphery. Dose distributions for axial CT scans were measured on a 64-slice multidetector CT (MDCT) scanner (GE Healthcare, Chalfont St. Giles, UK). The same measurements were simulated using a Monte Carlo code (PENELOPE, Universität de Barcelona) with the applicable CT geometry including bowtie filter. The deviations between simulated and measured dose values were generally within 5%. To our knowledge, this work is one of the first attempts to compare measured radial dose distributions on a cylindrical phantom with Monte Carlo simulated results. It provides a simple and effective method for benchmarking organ dose simulation codes and demonstrates the potential of Monte Carlo simulation for investigating the relationship between dose and image quality for pediatric CT patients.

Authors
Xiang, L; Samei, E; Yoshizumi, T; Colsher, JG; Jones, RP; Frush, DP
MLA Citation
Xiang, L, Samei, E, Yoshizumi, T, Colsher, JG, Jones, RP, and Frush, DP. "Experimental benchmarking of a Monte Carlo dose simulation code for pediatric CT." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6510.PART 2 (2007).
Source
scival
Published In
Proceedings of SPIE
Volume
6510
Issue
PART 2
Publish Date
2007
DOI
10.1117/12.713728

Initial human subject results for breast Bi-plane correlation imaging technique

Computer aided detection (CADe) systems often present multiple false-positives per image in projection mammography due to overlapping anatomy. To reduce the number of such false-positives, we propose performing CADe on image pairs acquired using a bi-plane correlation imaging (BCI) technique. In this technique, images are acquired of each breast at two different projection angles. A traditional CADe algorithm operates on each image to identify suspected lesions. The suspicious areas from both projections are then geometrically correlated, eliminating any lesion that is not identified on both views. Proof of concept studies showed that that the BCI technique reduced the numbers of false-positives per case up to 70%. (This work was supported in part by grants from the Department of Defense (USAMRMC W81XWH-04-1-0323), Komen Foundation (PDF55806), NIH (R01-CA-109074 and R01-CA-112437), Cancer Research and Prevention Foundation, and a research agreement with Siemens Medical Solutions.).

Authors
Jr, RSS; Samei, E; Majdi-Nasab, N; Lo, JY
MLA Citation
Jr, RSS, Samei, E, Majdi-Nasab, N, and Lo, JY. "Initial human subject results for breast Bi-plane correlation imaging technique." 2007.
Source
scival
Published In
Proceedings of SPIE
Volume
6514
Issue
PART 2
Publish Date
2007
DOI
10.1117/12.713722

Visual image quality metrics for optimization of breast tomosynthesis acquisition technique

Breast tomosynthesis is currently an investigational imaging technique requiring optimization of its many combinations of data acquisition and image reconstruction parameters for optimum clinical use. In this study, the effects of several acquisition parameters on the visual conspicuity of diagnostic features were evaluated for three breast specimens using a visual discrimination model (VDM). Acquisition parameters included total exposure, number of views, full resolution and binning modes, and lag correction. The diagnostic features considered in these specimens were mass margins, microcalcifications, and mass spicules. Metrics of feature contrast were computed for each image by defining two regions containing the selected feature (Signal) and surrounding background (Noise), and then computing the difference in VDM channel metrics between Signal and Noise regions in units of just-noticeable differences (JNDs). Scans with 25 views and exposure levels comparable to a standard two-view mammography exam produced higher levels of feature contrast. The effects of binning and lag correction on feature contrast were found to be generally small and isolated, consistent with our visual assessments of the images. Binning produced a slight loss of spatial resolution which could be compensated in the reconstruction filter. These results suggest that good image quality can be achieved with the faster and therefore more clinically practical 25-view scans with binning, which can be performed in as little as 12.5 seconds. Further work will investigate other specimens as well as alternate figures of merit in order to help determine optimal acquisition and reconstruction parameters for clinical trials.

Authors
Johnson, JP; Lo, J; Mertelmeier, T; Nafziger, JS; Timberg, P; Samei, E
MLA Citation
Johnson, JP, Lo, J, Mertelmeier, T, Nafziger, JS, Timberg, P, and Samei, E. "Visual image quality metrics for optimization of breast tomosynthesis acquisition technique." 2007.
Source
scival
Published In
Proceedings of SPIE
Volume
6515
Publish Date
2007
DOI
10.1117/12.712343

Design of a new multi-projection imaging system for chest radiography

Overlapping anatomical structures may confound detection of lung nodules in conventional projection chest radiography. To alleviate the visual clutter due to overlying anatomy, a dedicated digital multi-projection system for chest imaging was recently developed at the Radiology Department of Duke University. The system has a translating x-ray tube and acquires multiple projections of the same patient in rapid succession from slightly different angles about the posterioranterior (PA) orientation. Geometric correlation information across these multiple projections is used to positively identify suspicious nodules and reduce false alarms. The unique feature of this system is that it can acquire images along both the horizontal and vertical axes and is therefore capable of traversing an arbitrary trajectory on a plane parallel to the detector. We are reporting the physical design considerations in the development of the multi-projection imaging system and the initial performance in our ongoing clinical trials using the system. Future application in correlation imaging and stereoscopic imaging are also noted. © 2007 IEEE.

Authors
Chawla, AS; Boyce, S; Samei, E
MLA Citation
Chawla, AS, Boyce, S, and Samei, E. "Design of a new multi-projection imaging system for chest radiography." IEEE Nuclear Science Symposium Conference Record 4 (2007): 2996-2999.
Source
scival
Published In
IEEE Nuclear Science Symposium Conference Record
Volume
4
Publish Date
2007
Start Page
2996
End Page
2999
DOI
10.1109/NSSMIC.2007.4436764

Geometrical repeatability and motion blur analysis of a new multi-projection X-ray imaging system

We report on the reproducibility and tests for possible motion blur artifacts of a new high frame-rate prototype x-ray multi-projection system recently installed in the Radiology Department of Duke University. The system, which has a translating x-ray tube but a stationary detector, is capable of acquiring oblique-angled full field projection images along both the vertical and horizontal axes at variable speeds and acquisition frame rates. The angular span of the tube movement is +7.5° to -7.5° about the posterior-anterior (PA) orientation. To analyze the effect of possible blurring artifact due to motion of the x-ray tube, multi-angled projection images of an edge device were acquired. The Modulation Transfer Function (MTF) determined from the PA projection acquired with and without the tube in motion was compared to investigate blur artifacts that may be introduced due to motion of the x-ray tube. Geometrical precision of the system was assessed at two tube speeds by evaluating the recorded position coordinates as well as edge positions in repeated acquisitions. Excellent geometrical consistency was found in the tube motion. The positional errors at tube speeds of 1 and 2 in/sec were found to be within 1%. The possible effect on the MTF due to motion of the tube was found to be inconsequential. The system was deemed ready for actual clinical trials with these acquisition parameters. © 2006 IEEE.

Authors
Chawla, AS; Samei, E
MLA Citation
Chawla, AS, and Samei, E. "Geometrical repeatability and motion blur analysis of a new multi-projection X-ray imaging system." IEEE Nuclear Science Symposium Conference Record 5 (2007): 3170-3173.
Source
scival
Published In
IEEE Nuclear Science Symposium Conference Record
Volume
5
Publish Date
2007
Start Page
3170
End Page
3173
DOI
10.1109/NSSMIC.2006.356548

Validation of software for QC assessment of MTF and NPS

Modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) are widely accepted measures of digital radiographic system performance. However the implementation of these measurement methodologies has been limited to a handful of researchers using an assortment of techniques. A prototype edge tool and easy-to-use software program, which can generate MTF, NPS, and DQE results quickly and easily in the field, have been developed. The edge tool consists of 1mm or 250 μ thick tungsten with two polished edges. Edge and NPS data were obtained and analyzed by 3 investigators using three analysis methods: Method A, the software under development for this report; Method B, code available on the web site of one of the investigators [Saunders and Samei, Med. Phys. 33, 308-319 (2006)]; and Method C, code developed by two other of the investigators [Samei and Flynn, Med Phy. 30, 608-622, (2003)]. In all cases the differences between the results using Method B and Method A were less than 1%. The differences between Method A and Method C were larger, up to 5.26%. NPS were calculated using Method A and B. The results were very close, with average errors less than 2.5% for exposures of 27.3, 9.3, and 2.7 uGy. Analysis of data for a 10 cm misalignment shows no significant error for either the 250μ or 1mm edge. The method developed gives results that correlate closely with results obtained from established methods. The software is easy-to-use and flexible in its application. The Edge Tool developed has the necessary precision to accurately determine the MTF values of the system. Further validation of NPS and DQE is ongoing.

Authors
Peppler, W; Hong, W; Steinhauser, R; Whiting, B; Samei, E; Flynn, M; Don, S; Corradini, N
MLA Citation
Peppler, W, Hong, W, Steinhauser, R, Whiting, B, Samei, E, Flynn, M, Don, S, and Corradini, N. "Validation of software for QC assessment of MTF and NPS." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6510.PART 3 (2007).
Source
scival
Published In
Proceedings of SPIE
Volume
6510
Issue
PART 3
Publish Date
2007
DOI
10.1117/12.713434

A contrast-detail comparison of computed mammotomography and digital mammography

We use a contrast-detail observer study to compare performance of a novel 3D computed mammotomography (CmT) system with a commercially developed full-field digital mammography (FFDM) system. A contrast-detail phantom comprised of uniform acrylic spheres of various diameters was developed and placed in a variety of mediums including uniform water (simulating low contrast lesions within a uniform background), water and acrylic yarn (simulating low contrast lesions with over/under-lying structure), oil only (simulating higher contrast lesions in a uniform background), and oil and acrylic yarn (simulating higher contrast lesions with over/under-lying structure). For CmT, the phantom was placed in a 14.6 cm diameter uncompressed breast phantom and projections acquired using a simple circular orbit, W-target tube, 60 kVp tube potential, 0.05 cm Ce filtration, 4 mAs per projection, and a CsI(Tl) digital x-ray detector. Reconstructions used an iterative OSTR algorithm. For FFDM, the phantom was placed in a 5.3-cm-thick compressed breast phantom. Single CC-view mammograms were acquired using a clinical W-target tube with 50 um Rh filtration, 28 kVp, photo-timed mAs per our clinical mammography operation, and a Selenium-based flat-panel detector (Mammomat Novation, Siemens). Six observers evaluated the images in terms of the number of detectable spheres. FFDM performed significantly better for the low contrast lesions in uniform water background (p<0.05). However, CmT performed significantly better for all other cases (p<0.05). Results indicate that CmT shows significant advantage in soft tissue detection over FFDM in otherwise low contrast dense breasts.

Authors
McKinley, RL; Tornai, MP; Floyd, CE; Samei, E
MLA Citation
McKinley, RL, Tornai, MP, Floyd, CE, and Samei, E. "A contrast-detail comparison of computed mammotomography and digital mammography." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6510.PART 1 (2007).
Source
scival
Published In
Proceedings of SPIE
Volume
6510
Issue
PART 1
Publish Date
2007
DOI
10.1117/12.713032

An anger-camera study of scatter effects in single-photon-emission imaging with flat-panel detectors

Authors
Bowsher, JE; Yin, F; Greer, KL; Chawla, A; Samei, E; Willett, CG
MLA Citation
Bowsher, JE, Yin, F, Greer, KL, Chawla, A, Samei, E, and Willett, CG. "An anger-camera study of scatter effects in single-photon-emission imaging with flat-panel detectors." 2007.
Source
wos-lite
Published In
International Journal of Radiation Oncology, Biology, Physics
Volume
69
Issue
3
Publish Date
2007
Start Page
S727
End Page
S727
DOI
10.1016/j.ijrobp.2007.07.2124

Improving mammographic decision accuracy by incorporating observer ratings with interpretation time.

Mammography is currently the most established technique for the early detection of breast cancer. However, mammography would benefit from further improvements as it does produce some errors, such as not finding all early-stage cancers. The objectives of this study were first, to measure the timing of correct and incorrect reading decisions in mammography and second, to exploit those dependencies to improve accuracy in mammographic interpretation. To address these objectives, an experiment was conducted where experienced breast imaging radiologists reviewed 400 mammographic regions equally divided among images that contained simulated benign masses, malignant masses, malignant microcalcifications and no lesions. The experiment recorded the radiologists' decision as well as the length of time the mammogram was interpreted in. The experiment results showed that incorrect detection as well as incorrect classification decisions were associated with longer interpretation times (p<0.0001). The timing results were used to create a model that would flag cases for review that had a higher probability of error. The flagged cases had a median accuracy drop of 13% for detection decisions and 16% for classification decisions compared with unflagged cases. This suggests that interpretation time can be incorporated into mammographic decision-making in order to identify cases with higher probabilities of perceptual error that require further review.

Authors
Saunders, RS; Samei, E
MLA Citation
Saunders, RS, and Samei, E. "Improving mammographic decision accuracy by incorporating observer ratings with interpretation time." Br J Radiol 79 Spec No 2 (December 2006): S117-S122.
PMID
17209116
Source
pubmed
Published In
British Journal of Radiology
Volume
79 Spec No 2
Publish Date
2006
Start Page
S117
End Page
S122
DOI
10.1259/bjr/96931332

Recent advances in chest radiography.

There have been many remarkable advances in conventional thoracic imaging over the past decade. Perhaps the most remarkable is the rapid conversion from film-based to digital radiographic systems. Computed radiography is now the preferred imaging modality for bedside chest imaging. Direct radiography is rapidly replacing film-based chest units for in-department posteroanterior and lateral examinations. An exciting aspect of the conversion to digital radiography is the ability to enhance the diagnostic capabilities and influence of chest radiography. Opportunities for direct computer-aided detection of various lesions may enhance the radiologist's accuracy and improve efficiency. Newer techniques such as dual-energy and temporal subtraction radiography show promise for improved detection of subtle and often obscured or overlooked lung lesions. Digital tomosynthesis is a particularly promising technique that allows reconstruction of multisection images from a short acquisition at very low patient dose. Preliminary data suggest that, compared with conventional radiography, tomosynthesis may also improve detection of subtle lung lesions. The ultimate influence of these new technologies will, of course, depend on the outcome of rigorous scientific validation.

Authors
McAdams, HP; Samei, E; Dobbins, J; Tourassi, GD; Ravin, CE
MLA Citation
McAdams, HP, Samei, E, Dobbins, J, Tourassi, GD, and Ravin, CE. "Recent advances in chest radiography." Radiology 241.3 (December 2006): 663-683. (Review)
PMID
17114619
Source
pubmed
Published In
Radiology
Volume
241
Issue
3
Publish Date
2006
Start Page
663
End Page
683
DOI
10.1148/radiol.2413051535

Comparison of LCD and CRT displays based on efficacy for digital mammography.

RATIONALE AND OBJECTIVES: To compare two display technologies, cathode ray tube (CRT) and liquid crystal display (LCD), in terms of diagnostic accuracy for several common clinical tasks in digital mammography. MATERIALS AND METHODS: Simulated masses and microcalcifications were inserted into normal digital mammograms to produce an image set of 400 images. Images were viewed on one CRT and one LCD medical-quality display device by five experienced breast-imaging radiologists who rated the images using a categorical rating paradigm. The observer data were analyzed to determine overall classification accuracy, overall lesion detection accuracy, and accuracy for four specific diagnostic tasks: detection of benign masses, malignant masses, and microcalcifications, and discrimination of benign and malignant masses. RESULTS: Radiologists had similar overall classification accuracy (LCD: 0.83 +/- 0.01, CRT: 0.82 +/- 0.01) and lesion detection accuracy (LCD: 0.87 +/- 0.01, CRT: 0.85 +/- 0.01) on both displays. The difference in accuracy between LCD and CRT for the detection of benign masses, malignant masses, and microcalcifications, and discrimination of benign and malignant masses was -0.019 +/- 0.009, 0.020 +/- 0.008, 0.012 +/- 0.013, and 0.0094 +/- 0.011, respectively. Overall, the two displays did not exhibit any statistically significant difference (P > .05). CONCLUSION: This study explored the suitability of two different soft-copy displays for the viewing of mammographic images. It found that LCD and CRT displays offer similar clinical utility for mammographic tasks.

Authors
Saunders, RS; Samei, E; Baker, J; Delong, D; Soo, MS; Walsh, R; Pisano, E; Kuzmiak, CM; Pavic, D
MLA Citation
Saunders, RS, Samei, E, Baker, J, Delong, D, Soo, MS, Walsh, R, Pisano, E, Kuzmiak, CM, and Pavic, D. "Comparison of LCD and CRT displays based on efficacy for digital mammography." Acad Radiol 13.11 (November 2006): 1317-1326.
PMID
17070449
Source
pubmed
Published In
Academic Radiology
Volume
13
Issue
11
Publish Date
2006
Start Page
1317
End Page
1326
DOI
10.1016/j.acra.2006.07.017

Optimized radiographic spectra for small animal digital subtraction angiography.

The increasing use of small animals in basic research has spurred interest in new imaging methodologies. Digital subtraction angiography (DSA) offers a particularly appealing approach to functional imaging in the small animal. This study examines the optimal x-ray, molybdenum (Mo) or tungsten (W) target sources, and technique to produce the highest quality small animal functional subtraction angiograms in terms of contrast and signal-difference-to-noise ratio squared (SdNR2). Two limiting conditions were considered-normalization with respect to dose and normalization against tube loading. Image contrast and SdNR2 were simulated using an established x-ray model. DSA images of live rats were taken at two representative tube potentials for the W and Mo sources. Results show that for small animal DSA, the Mo source provides better contrast. However, with digital detectors, SdNR2 is the more relevant figure of merit. The W source operated at kVps >60 achieved a higher SdNR2. The highest SdNR2 was obtained at voltages above 90 kVp. However, operation at the higher potential results in significantly greater dose and tube load and reduced contrast quantization. A reasonable tradeoff can be achieved at tube potentials at the beginning of the performance plateau, around 70 kVp, where the relative gain in SdNR2 is the greatest.

Authors
Lin, MD; Samei, E; Badea, CT; Yoshizumi, TT; Johnson, GA
MLA Citation
Lin, MD, Samei, E, Badea, CT, Yoshizumi, TT, and Johnson, GA. "Optimized radiographic spectra for small animal digital subtraction angiography." Med Phys 33.11 (November 2006): 4249-4257.
PMID
17153403
Source
pubmed
Published In
Medical physics
Volume
33
Issue
11
Publish Date
2006
Start Page
4249
End Page
4257
DOI
10.1118/1.2356646

Visual assessment of angular response in medical liquid crystal displays.

In spite of having non-Lambertian emission, displays based on liquid crystal technology are becoming popular for medical diagnostic work stations. For all liquid crystal displays (LCDs), the contrast performance varies with viewing direction. Accurate measurements of the angular distribution of light emission require expensive instrumentation and extensive expertise. We investigated the possibility of using a test pattern to visually assess the angular response performance of LCDs. We found that this procedure offers the end user of displays a simple, fast, and relatively consistent technique to verify that the viewing angle performance of the display device is within certain acceptable limits.

Authors
Badano, A; Schneider, S; Samei, E
MLA Citation
Badano, A, Schneider, S, and Samei, E. "Visual assessment of angular response in medical liquid crystal displays." J Digit Imaging 19.3 (September 2006): 240-248.
PMID
16741662
Source
pubmed
Published In
Journal of Digital Imaging
Volume
19
Issue
3
Publish Date
2006
Start Page
240
End Page
248
DOI
10.1007/s10278-006-0633-5

Digital mammography image quality: image display.

This paper on digital mammography image display is 1 of 3 papers written as part of an intersociety effort to establish image quality standards for digital mammography. The information included in this paper is intended to support the development of an American College of Radiology (ACR) guideline on image quality for digital mammography. The topics of the other 2 papers are digital mammography image acquisition and digital mammography image storage, transmission, and retrieval. The societies represented in compiling this document were the Radiological Society of North America, the ACR, the American Association of Physicists in Medicine, and the Society for Computer Applications in Radiology. These papers describe in detail what is known to improve image quality for digital mammography and make recommendations about how digital mammography should be performed to optimize the visualization of breast cancers using this imaging tool. Through the publication of these papers, the ACR is seeking input from industry, radiologists, and other interested parties on their contents so that the final ACR guideline for digital mammography will represent the consensus of the broader community interested in these topics.

Authors
Siegel, E; Krupinski, E; Samei, E; Flynn, M; Andriole, K; Erickson, B; Thomas, J; Badano, A; Seibert, JA; Pisano, ED
MLA Citation
Siegel, E, Krupinski, E, Samei, E, Flynn, M, Andriole, K, Erickson, B, Thomas, J, Badano, A, Seibert, JA, and Pisano, ED. "Digital mammography image quality: image display." J Am Coll Radiol 3.8 (August 2006): 615-627.
PMID
17412136
Source
pubmed
Published In
Journal of the American College of Radiology
Volume
3
Issue
8
Publish Date
2006
Start Page
615
End Page
627
DOI
10.1016/j.jacr.2006.03.007

Simulation of mammographic lesions.

RATIONALE AND OBJECTIVES: This study presents a method for generating breast masses and microcalcifications in mammography via simulation. This simulation method allows for the creation of large image datasets with particular lesions, which may serve as a useful tool for perception studies measuring imaging system performance. MATERIALS AND METHODS: The study first characterized the radiographic appearance of both masses and microcalcifications, examining the following five properties: contrast, edge gradient profile of masses, edge characteristics of masses, shapes of individual microcalcifications, and shapes of microcalcification distributions. The characterization results then guided the development of routines that created simulated masses and microcalcifications. The quality of the simulations was verified by experienced breast imaging radiologists who evaluated simulated and real lesions and rated whether a given lesion had a realistic appearance. RESULTS: The radiologists rated real and simulated lesions to have similarly realistic appearances. Using receiver operating characteristic analysis to characterize the degree of similarity, the results showed an A(z) of 0.68 +/- 0.07 for benign masses, 0.65 +/- 0.07 for malignant masses, and 0.62 +/- 0.07 for microcalcifications, thus showing notable overlap in the simulated and real lesion ratings. CONCLUSION: This research introduced a new approach for simulating breast masses and microcalcifications that relied on anatomic characteristics measured from real lesions. Results from an observer performance experiment indicate that our simulation routine produced realistic simulations of masses and microcalcifications as judged by expert radiologists.

Authors
Saunders, R; Samei, E; Baker, J; Delong, D
MLA Citation
Saunders, R, Samei, E, Baker, J, and Delong, D. "Simulation of mammographic lesions." Acad Radiol 13.7 (July 2006): 860-870.
PMID
16777560
Source
pubmed
Published In
Academic Radiology
Volume
13
Issue
7
Publish Date
2006
Start Page
860
End Page
870
DOI
10.1016/j.acra.2006.03.015

Contrast-detail analysis of three flat panel detectors for digital radiography.

In this paper we performed a contrast detail analysis of three commercially available flat panel detectors, two based on the indirect detection mechanism (GE Revolution XQ/i, system A, and Trixell/Philips Pixium 4600, system B) and one based on the direct detection mechanism (Hologic DirectRay DR 1000, system C). The experiment was conducted using standard x-ray radiation quality and a widely used contrast-detail phantom. Images were evaluated using a four alternative forced choice paradigm on a diagnostic-quality softcopy monitor. At the low and intermediate exposures, systems A and B gave equivalent performances. At the high dose levels, system A performed better than system B in the entire range of target sizes, even though the pixel size of system A was about 40% larger than that of system B. At all the dose levels, the performances of the system C (direct system) were lower than those of system A and B (indirect systems). Theoretical analyses based on the Perception Statistical Model gave similar predicted SNRT values corresponding to an observer efficiency of about 0.08 for systems A and B and 0.05 for system C.

Authors
Borasi, G; Samei, E; Bertolini, M; Nitrosi, A; Tassoni, D
MLA Citation
Borasi, G, Samei, E, Bertolini, M, Nitrosi, A, and Tassoni, D. "Contrast-detail analysis of three flat panel detectors for digital radiography." Med Phys 33.6 (June 2006): 1707-1719.
PMID
16872078
Source
pubmed
Published In
Medical physics
Volume
33
Issue
6
Publish Date
2006
Start Page
1707
End Page
1719
DOI
10.1118/1.2191014

Assessment of detective quantum efficiency: Inter-comparison of IEC 62220-1 with representative prior methods

Authors
Ranger, NT; Samei, E; Dobbins, JT; Ravin, CE
MLA Citation
Ranger, NT, Samei, E, Dobbins, JT, and Ravin, CE. "Assessment of detective quantum efficiency: Inter-comparison of IEC 62220-1 with representative prior methods." June 2006.
Source
wos-lite
Published In
Medical physics
Volume
33
Issue
6
Publish Date
2006
Start Page
2007
End Page
2007
DOI
10.1118/1.2240288

Display evaluation demonstration workshop: Part II

Authors
Samei, E
MLA Citation
Samei, E. "Display evaluation demonstration workshop: Part II." June 2006.
Source
wos-lite
Published In
Medical physics
Volume
33
Issue
6
Publish Date
2006
Start Page
2176
End Page
2177
DOI
10.1118/1.2241477

Does image quality impact mammographic accuracy?

Authors
Jr, SRS; Samei, E
MLA Citation
Jr, SRS, and Samei, E. "Does image quality impact mammographic accuracy?." June 2006.
Source
wos-lite
Published In
Medical physics
Volume
33
Issue
6
Publish Date
2006
Start Page
2265
End Page
2266
DOI
10.1118/1.2241844

Evaluation of medical displays

Authors
Samei, E
MLA Citation
Samei, E. "Evaluation of medical displays." June 2006.
Source
wos-lite
Published In
Medical physics
Volume
33
Issue
6
Publish Date
2006
Start Page
2169
End Page
2169
DOI
10.1118/1.2241446

Preliminary investigations into combined CT/SPECT imaging onboard therapy machines

Authors
Bowsher, J; Yin, F; Greer, K; Jaszczak, R; Samei, E; Willett, C
MLA Citation
Bowsher, J, Yin, F, Greer, K, Jaszczak, R, Samei, E, and Willett, C. "Preliminary investigations into combined CT/SPECT imaging onboard therapy machines." June 2006.
Source
wos-lite
Published In
Medical physics
Volume
33
Issue
6
Publish Date
2006
Start Page
2221
End Page
2221
DOI
10.1118/1.2241651

Intercomparison of methods for image quality characterization. II. Noise power spectrum.

Second in a two-part series comparing measurement techniques for the assessment of basic image quality metrics in digital radiography, in this paper we focus on the measurement of the image noise power spectrum (NPS). Three methods were considered: (1) a method published by Dobbins et al. [Med. Phys. 22, 1581-1593 (1995)], (2) a method published by Samei et al. [Med. Phys. 30, 608-622 (2003)], and (3) a new method sanctioned by the International Electrotechnical Commission (IEC 62220-1, 2003), developed as part of an international standard for the measurement of detective quantum efficiency. In addition to an overall comparison of the estimated NPS between the three techniques, the following factors were also evaluated for their effect on the measured NPS: horizontal versus vertical directional dependence, the use of beam-limiting apertures, beam spectrum, and computational methods of NPS analysis, including the region-of-interest (ROI) size and the method of ROI normalization. Of these factors, none was found to demonstrate a substantial impact on the amplitude of the NPS estimates (< or = 3.1% relative difference in NPS averaged over frequency, for each factor considered separately). Overall, the three methods agreed to within 1.6% +/- 0.8% when averaged over frequencies > 0.15 mm(-1).

Authors
Dobbins, JT; Samei, E; Ranger, NT; Chen, Y
MLA Citation
Dobbins, JT, Samei, E, Ranger, NT, and Chen, Y. "Intercomparison of methods for image quality characterization. II. Noise power spectrum." Med Phys 33.5 (May 2006): 1466-1475.
PMID
16752581
Source
pubmed
Published In
Medical physics
Volume
33
Issue
5
Publish Date
2006
Start Page
1466
End Page
1475
DOI
10.1118/1.2188819

Intercomparison of methods for image quality characterization. I. Modulation transfer function.

The modulation transfer function (MTF) and the noise power spectrum (NPS) are widely recognized as the most relevant metrics of resolution and noise performance in radiographic imaging. These quantities have commonly been measured using various techniques, the specifics of which can have a bearing on the accuracy of the results. As a part of a study aimed at comparing the relative performance of different techniques, in this paper we report on a comparison of two established MTF measurement techniques: one using a slit test device [Dobbins et al., Med. Phys. 22, 1581-1593 (1995)] and another using a translucent edge test device [Samei et al., Med. Phys. 25, 102-113 (1998)], with one another and with a third technique using an opaque edge test device recommended by a new international standard (IEC 62220-1, 2003). The study further aimed to substantiate the influence of various acquisition and processing parameters on the estimated MTF. The slit test device was made of 2 mm thick Pb slabs with a 12.5 microm opening. The translucent edge test device was made of a laminated and polished Pt(0.9)Ir(0.1). alloy foil of 0.1 mm thickness. The opaque edge test device was made of a 2 mm thick W slab. All test devices were imaged on a representative indirect flat-panel digital radiographic system using three published beam qualities: 70 kV with 0.5 mm Cu filtration, 70 kV with 19 mm Al filtration, and 74 kV with 21 mm Al filtration (IEC-RQA5). The latter technique was also evaluated in conjunction with two external beam-limiting apertures (per IEC 62220-1), and with the tube collimator limiting the beam to the same area achieved with the apertures. The presampled MTFs were deduced from the acquired images by Fourier analysis techniques, and the results analyzed for relative values and the influence of impacting parameters. The findings indicated that the measurement technique has a notable impact on the resulting MTF estimate, with estimates from the overall IEC method 4.0% +/- 0.2% lower than that of Dobbins et al. and 0.7% +/- 0.4% higher than that of Samei et al. averaged over the zero to cutoff frequency range. Over the same frequency range, keeping beam quality and limitation constant, the average MTF estimate obtained with the edge techniques differed by up to 5.2% +/- 0.2% from that of the slit, with the opaque edge providing lower MTF estimates at lower frequencies than those obtained with the translucent edge or slit. The beam quality impacted the average estimated MTF by as much as 3.7% +/- 0.9% while the use of beam limiting devices alone increased the average estimated MTF by as much as 7.0% +/- 0.9%. While the slit method is inherently very sensitive to misalignment, both edge techniques were found to tolerate misalignments by as much as 6 cm. The results suggest the use of the opaque edge test device and the tube internal collimator for beam limitation in order to achieve an MTF result most reflective of the overall performance of the imaging system and least susceptible to misalignment and scattered radiation. Careful attention to influencing factors is warranted to achieve accurate results.

Authors
Samei, E; Ranger, NT; Dobbins, JT; Chen, Y
MLA Citation
Samei, E, Ranger, NT, Dobbins, JT, and Chen, Y. "Intercomparison of methods for image quality characterization. I. Modulation transfer function." Med Phys 33.5 (May 2006): 1454-1465.
PMID
16752580
Source
pubmed
Published In
Medical physics
Volume
33
Issue
5
Publish Date
2006
Start Page
1454
End Page
1465
DOI
10.1118/1.2188816

Imaging properties of digital magnification radiography.

Flat panel detectors exhibit improved signal-to-noise ratio (SNR) and display capabilities compared to film. This improvement necessitates a new evaluation of optimal geometry for conventional projection imaging applications such as digital projection mammography as well as for advanced x-ray imaging applications including cone-beam computed tomography (CT), tomosynthesis, and mammotomography. Such an evaluation was undertaken in this study to examine the effects of x-ray source distribution, inherent detector resolution, magnification, scatter rejection, and noise characteristics including noise aliasing. A model for x-ray image acquisition was used to develop generic results applicable to flat panel detectors with similar x-ray absorption characteristics. The model assumed a Gaussian distribution for the focal spot and a rectangular distribution for a pixel. A generic model for the modulated transfer function (MTF) of indirect flat panel detectors was derived by a nonlinear fit of empirical receptor data to the Burgess model for phosphor MTFs. Noise characteristics were investigated using a generic noise power spectrum (NPS) model for indirect phosphor-based detectors. The detective quantum efficiency (DQE) was then calculated from the MTF and NPS models. The results were examined as a function of focal spot size (0.1, 0.3, and 0.6 mm) and pixel size (50, 100, 150, and 200 microm) for magnification ranges 1 to 3. Mammography, general radiography (also applicable to mammotomography), and chest radiography applications were explored using x-ray energies of 28, 74, and 120 kVp, respectively. Nodule detection was examined using the effective point source scatter model, effective DQE, and the Hotelling SNR2 efficiency. Results indicate that magnification can potentially improve the signal and noise performance of digital images. Results also show that a cross over point occurs in the spatial frequency above and below which the effects of magnification differ indicating that there are task dependent tradeoffs associated with magnification. The cross over point varies depending upon focal spot size, pixel size, x-ray energy, and source-to-image-distance (SID). For mammography, the cross over point occurs for a 0.3 mm focal spot while a 0.6 mm focal spot indicates that magnification does not improve image quality due to focal spot blurring. Thus, the benefit of magnification may be limited. For general radiography (as well as mammotomography), and chest radiography, the cross over point changes with SID. For a system with a 0.3 mm focal spot, 100 microm pixel size, a 2 m SID, and the applicable tissue thickness and scatter components, optimal magnification improved SNR2 by approximately 1.2 times for mammography and 1.5 times for general radiography (and mammotomography). These results indicate that the optimal geometry can improve image quality without changing patient dose or otherwise reduce dose without compromising image quality.

Authors
Boyce, SJ; Samei, E
MLA Citation
Boyce, SJ, and Samei, E. "Imaging properties of digital magnification radiography." Med Phys 33.4 (April 2006): 984-996.
PMID
16696475
Source
pubmed
Published In
Medical physics
Volume
33
Issue
4
Publish Date
2006
Start Page
984
End Page
996
DOI
10.1118/1.2174133

Viewing angle performance of medical liquid crystal displays.

Cathode-ray tube (CRT) and liquid crystal display (LCD) are currently two main technologies for displaying medical images. LCDs possess a number of advantages, but their performance varies as a function of viewing angle. Our purpose in this study was to characterize the angular response performance of five medical-grade LCDs, and to substantiate their impact on their compliance with the DICOM gray scale display function (GSDF). Furthermore, the study aimed to test a framework to define an angular acceptance range for medical LCDs based on the recent AAPM TG18 guidelines. Measurements were made on five calibrated dual-domain LCDs, including two 3 megapixel monochrome LCDs, two 5 megapixel monochrome LCDs, and one 9 megapixel color LCD. The luminance performance of each display device was measured as a function of the viewing angle at 17 discrete levels using TG18-LN test patterns and a Fourier-optics-based luminance meter. The luminance data were analyzed according to the AAPM TG18 methodology. The displays showed notable variation in luminance and contrast performance as a function of the viewing angle, particularly in diagonal viewing orientations. Overall, the luminance ratio remained greater than 175 within +/-20 degrees and +/-33 degrees viewing angle cones (beta175 = 20 degrees-33 degrees). Aiming to maintain a maximum deviation from the GSDF contrast less than 0.3, i.e., kappa17 < or = 0.3, acceptable viewing angle cones of +/-22 degrees and +/-35 degrees were indicated (alpha 0.3= 22 degrees-35 degrees). The findings demonstrate the significant impact of angular response on image contrast, and the utility of alpha 0.3 and beta175 quantities for defining the viewing angle cones within which a medical LCD device can be effectively utilized.

Authors
Samei, E; Wright, SL
MLA Citation
Samei, E, and Wright, SL. "Viewing angle performance of medical liquid crystal displays." Med Phys 33.3 (March 2006): 645-654.
PMID
16878568
Source
pubmed
Published In
Medical physics
Volume
33
Issue
3
Publish Date
2006
Start Page
645
End Page
654
DOI
10.1118/1.2168430

Simulation of liver lesions for pediatric CT.

PURPOSE: To develop and validate a technique based on characteristics of real lesions for simulating realistic small liver lesions on pediatric computed tomographic (CT) images. MATERIALS AND METHODS: The institutional review board provided exempt status for this study, determined that it was not subject to HIPAA compliance, and did not require informed consent. Patient identification information was removed from clinical images from contrast material-enhanced multi-detector row CT examinations performed in 10 children. Patients were infants or children up to 18 years old. Information about sex was not available. Children had one or more liver lesions of 2-6 mm in maximum transverse diameter. Images with more than one lesion were rendered multiple times, and each time, all but one of the lesions were digitally removed in sequence. This process provided images (n = 19) with a single real lesion. For consistency, the same image backgrounds (images with all real lesions removed) were used to create an identical number of images (n = 19), each with a single simulated lesion. Subsequently, three radiologists independently assessed images of real and simulated lesions that were presented in random order with a score on a continuous scale of 0 (definitely simulated) to 100 (definitely real). Mixed-model analysis of variance was used to test the null hypothesis that the difference in population mean scores between the two lesion types was zero. RESULTS: The observer study did not reveal a significant difference in the ability of any radiologist to discriminate between real and simulated lesions (P > .31). The differences in mean scores for discrimination between real and simulated lesions for the three observers were -6, 9, and -7, respectively. The estimated overall difference was -1. CONCLUSION: Mathematic simulation of liver lesions is a feasible technique for creating realistic lesions for image quality or dose reduction studies in pediatric CT.

Authors
Hoe, CL; Samei, E; Frush, DP; Delong, DM
MLA Citation
Hoe, CL, Samei, E, Frush, DP, and Delong, DM. "Simulation of liver lesions for pediatric CT." Radiology 238.2 (February 2006): 699-705.
PMID
16371579
Source
pubmed
Published In
Radiology
Volume
238
Issue
2
Publish Date
2006
Start Page
699
End Page
705
DOI
10.1148/radiol.2381050477

Resolution and noise measurements of five CRT and LCD medical displays.

The performance of soft-copy displays plays a significant role in the overall image quality of a digital radiographic system. In this work, we discuss methods to characterize the resolution and noise of both cathode ray tube (CRT) and liquid crystal display (LCD) devices. We measured the image quality of five different commercial display devices, representing both CRT and LCD technologies, using a high-quality charge-coupled device (CCD) camera. The modulation transfer function (MTF) was calculated using the line technique, correcting for the MTF of the CCD camera and the display pixel size. The normalized noise power spectrum (NPS) was computed from two-dimensional Fourier analysis of uniform images. To separate the effects of pixel structure from interpixel luminance variations, we created structure-free images by eliminating the pixel structures of the display device. The NPS was then computed from these structure-free images to isolate interpixel luminance variations. We found that the MTF of LCDs remained close to the theoretical limit dictated by their inherent pixel size (0.85 +/- 0.08 at Nyquist frequency), in contrast to the MTF for the two CRT displays, which dropped to 0.15 +/- 0.08 at the Nyquist frequency. However, the NPS of LCDs showed significant peaks due to the subpixel structure, while the NPS of CRT displays exhibited a nearly flat power spectrum. After removing the pixel structure, the structured noise peaks for LCDs were eliminated and the overall noise magnitude was significantly reduced. The average total noise-to-signal ratio for CRT displays was 6.55% +/- 0.59%, of which 6.03% +/- 0.24% was due to interpixel luminance variations, while LCD displays had total noise to signal ratios of 46.1% +/- 5.1% of which 1.50% +/- 0.41% were due to interpixel luminance variations. Depending on the extent of the blurring and prewhitening processes of the human visual system, the magnitude of the display noise (including pixel structure) potentially perceived by the observer was reduced to 0.43% +/- 0.01% (accounting for blurring only) and 0.40 +/- 0.01% (accounting for blurring and prewhitening) for CRTs, and 1.02% +/- 0.22% (accounting for blurring only) and 0.36% +/- 0.08% (accounting for blurring and prewhitening) for LCDs.

Authors
Saunders, RS; Samei, E
MLA Citation
Saunders, RS, and Samei, E. "Resolution and noise measurements of five CRT and LCD medical displays." Med Phys 33.2 (February 2006): 308-319.
PMID
16532935
Source
pubmed
Published In
Medical physics
Volume
33
Issue
2
Publish Date
2006
Start Page
308
End Page
319
DOI
10.1118/1.2150777

Digital Mammography Image Quality: Image Display

This paper on digital mammography image display is 1 of 3 papers written as part of an intersociety effort to establish image quality standards for digital mammography. The information included in this paper is intended to support the development of an American College of Radiology (ACR) guideline on image quality for digital mammography. The topics of the other 2 papers are digital mammography image acquisition and digital mammography image storage, transmission, and retrieval. The societies represented in compiling this document were the Radiological Society of North America, the ACR, the American Association of Physicists in Medicine, and the Society for Computer Applications in Radiology. These papers describe in detail what is known to improve image quality for digital mammography and make recommendations about how digital mammography should be performed to optimize the visualization of breast cancers using this imaging tool. Through the publication of these papers, the ACR is seeking input from industry, radiologists, and other interested parties on their contents so that the final ACR guideline for digital mammography will represent the consensus of the broader community interested in these topics. © 2006 American College of Radiology.

Authors
Siegel, E; Krupinski, E; Samei, E; Flynn, M; Andriole, K; Erickson, B; Thomas, J; Badano, A; Seibert, JA; Pisano, ED
MLA Citation
Siegel, E, Krupinski, E, Samei, E, Flynn, M, Andriole, K, Erickson, B, Thomas, J, Badano, A, Seibert, JA, and Pisano, ED. "Digital Mammography Image Quality: Image Display." Journal of the American College of Radiology 3.8 (2006): 615-627.
Source
scopus
Published In
Journal of the American College of Radiology
Volume
3
Issue
8
Publish Date
2006
Start Page
615
End Page
627
DOI
10.1016/j.jacr.2006.03.007

Why Medical Image Perception?

Authors
Samei, E
MLA Citation
Samei, E. "Why Medical Image Perception?." Journal of the American College of Radiology 3.6 (2006): 400-401.
Source
scival
Published In
Journal of the American College of Radiology
Volume
3
Issue
6
Publish Date
2006
Start Page
400
End Page
401
DOI
10.1016/j.jacr.2006.02.017

A novel method to characterize the MTF in 3D for computed mammotomography

A novel phantom has been developed to measure the modulation transfer function (MTF) in 3D for x-ray computed tomography. The phantom consists of three tungsten wires, positioned nearly orthogonal to each other. Simultaneous measurements of the MTF are taken at various locations along the three orthogonal reconstructed planes. Our computed mammotomography (CmT) system uses a Varian Paxscan 2520 digital x-ray detector which can be positioned anywhere in ∼2pi steradian band and can have arbitrary trajectories, With a half-cone beam geometry and with the phantom positioned near the center of rotation, projection images are acquired over 360 degrees, Various 3D orbits are evaluated including vertical axis of rotation and saddle. Reconstructions were performed using an iterative ordered-subsets transmission algorithm on rebinned projection images, using various numbers of iterations. Rotation of reconstructed slices isolated each wire into its own plane. At various locations along the length of each wire, corresponding MTFs were calculated from 1D line spread functions. Through measurement, accuracy of wire method was verified by comparison of the projection MTFs computed from a wire and a standard edge device. Results indicated minor variations in MTF among the three orthogonal planes, which imply a high degree of uniform sampling in the imaged volume. Findings indicate that the phantom can be used to assess the intrinsic image resolution in 3D as well as potential degradative effects of measurements in various media.

Authors
Madhav, P; McKinley, RL; Samei, E; Bowsher, JE; Tornai, MP
MLA Citation
Madhav, P, McKinley, RL, Samei, E, Bowsher, JE, and Tornai, MP. "A novel method to characterize the MTF in 3D for computed mammotomography." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6142 II (2006).
Source
scival
Published In
Proceedings of SPIE
Volume
6142 II
Publish Date
2006
DOI
10.1117/12.653393

Analysis of a novel offset cone-beam computed mammotomography system geometry for accomodating various breast sizes.

We evaluate a newly developed dedicated cone-beam transmission computed mammotomography (CmT) system configuration using an optimized quasi-monochromatic cone beam technique for attenuation correction of SPECT in a planned dual-modality emission and transmission system for pendant, uncompressed breasts. In this study, we perform initial CmT acquisitions using various sized breast phantoms to evaluate an offset cone-beam geometry. This offset geometry provides conjugate projections through a full 360 degree gantry rotation, and thus yields a greatly increased effective field of view, allowing a much wider range of breast sizes to be imaged without truncation in reconstructed images. Using a tungsten X-ray tube and digital flat-panel X-ray detector in a compact geometry, we obtained initial CmT scans without shift and with the offset geometry, using geometrical frequency/resolution phantoms and two different sizes of breast phantoms. Acquired data were reconstructed using an ordered subsets transmission iterative algorithm. Projection images indicate that the larger, 20 cm wide, breast requires use of a half-cone-beam offset scan to eliminate truncation artifacts. Reconstructed image results illustrate elimination of truncation artifacts, and that the novel quasi-monochromatic beam yields reduced beam hardening. The offset geometry CmT system can indeed potentially be used for structural imaging and accurate attenuation correction for the functional dedicated breast SPECT system.

Authors
McKinley, RL; Tornai, MP; Brzymialkiewicz, C; Madhav, P; Samei, E; Bowsher, JE
MLA Citation
McKinley, RL, Tornai, MP, Brzymialkiewicz, C, Madhav, P, Samei, E, and Bowsher, JE. "Analysis of a novel offset cone-beam computed mammotomography system geometry for accomodating various breast sizes." Phys Med 21 Suppl 1 (2006): 48-55.
PMID
17645994
Source
pubmed
Published In
Physica Medica
Volume
21 Suppl 1
Publish Date
2006
Start Page
48
End Page
55
DOI
10.1016/S1120-1797(06)80024-4

In-field assessment of display resolution and noise: Performance evaluation of a commercial measurement system

Two key metrics of image quality for high-fidelity displays, including medical displays, are resolution and noise. Until now, these properties have been primarily measured in laboratory settings. For the first time, a system consisting of a CCD camera and analysis software has been made commercially available for measuring the resolution and noise of medical displays in a clinical setting. This study aimed at evaluating this new product in terms of accuracy and precision. In particular, the project involved the measurement of the modulation transfer function (MTF) and the signal-to-noise ratio (SNR) of two medical imaging displays, one cathode-ray tube (CRT) display and one liquid-crystal display (LCD) using this camera/software system. To assess the system's precision, measurements were made multiple times at the same setting. To check for accuracy, the results were compared with published values of the MTF and noise for the same displays. The performance of the system was also ascertained as a function of the focus setting of the camera. The results indicated that for the LCD, when the camera is focused within ±0.6 mm of the optimum focus setting, the MTF values lie within approximately 14% of the best focus MTF at the Nyquist frequency and 11 % of the optimum overall sharpness (∫ MTF2 df). Similar results were obtained in the horizontal and vertical directions. For the CRT, this focus produced vertical and horizontal MTF values at the Nyquist frequency within 15.2% and 61.2% of the optimum focus MTF, respectively. The figures in terms of overall sharpness were 3.0% and 0.7%. The results for the noise measurements showed a repeatability of 3% for the LCD and 13% for the CRT and a relative (but not absolute) magnitude of the noise between the two displays reflective of prior measurements. Overall, the measurement system yielded reasonably precise resolution and noise results for both display devices. The accuracy was traceable to published results only for the MTF and for relative level of display noise with differences in the absolute magnitude of noise between current and prior measurements attributed to variations in the non-standard techniques applied for display noise measurements. © Copyright 2006 Society for Information Display.

Authors
Samei, E; Cleland, E; Roehrig, H
MLA Citation
Samei, E, Cleland, E, and Roehrig, H. "In-field assessment of display resolution and noise: Performance evaluation of a commercial measurement system." Journal of the Society for Information Display 14.10 (2006): 839-845.
Source
scival
Published In
Journal of the Society for Information Display
Volume
14
Issue
10
Publish Date
2006
Start Page
839
End Page
845
DOI
10.1889/1.2372417

A photographic technique for assessing the viewing-angle performance of liquid-crystal displays

Liquid-crystal displays (LCDs) have notable variation in luminance and perceived contrast as a function of the angle from which they are viewed. Though this is an important performance issue for LCDs, most evaluation techniques for assessing this variation have been limited to laboratory settings. This study demonstrates the use of a photographic technique for such an evaluation. The technique is based on an actively cooled charge-coupled-device (CCD) detector in combination with a macro lens covering a circular angular range (8) of ±42.5°. The camera was used to evaluate the luminance and perceived contrast properties of an LCD. Uniform field images corresponding to 17 equally spaced gray-scale values in the digital driving level (DDL) range of the display system were acquired. The 12-bit gray-scale digital images produced by the camera were converted to luminance units (cd/m2) via the measured luminance vs. DDL response function of the camera. The changes in perceived contrast as a function of viewing angle were derived from the Barten model of the gray-scale response of the human-visual system using the methods proposed by the AAPM TC18 Report. The results of this photographic technique were compared to measurements acquired from a similar display using a Fourier-optics-based luminance meter. The results of the two methods generally agreed to within 5%. The photographic methods used were found to be accurate and robust for in-field assessment of the angular response of LCDs over the FOV of the camera. © Copyright 2006 Society for Information Display.

Authors
Fetterly, KA; Samei, E
MLA Citation
Fetterly, KA, and Samei, E. "A photographic technique for assessing the viewing-angle performance of liquid-crystal displays." Journal of the Society for Information Display 14.10 (2006): 867-872.
Source
scival
Published In
Journal of the Society for Information Display
Volume
14
Issue
10
Publish Date
2006
Start Page
867
End Page
872
DOI
10.1889/1.2372420

Biplane correlation imaging for lung nodule detection: Initial human subject results

In this paper, we present performance of biplane correlation imaging (BCI) on set of chest x-ray projections of human data. BCI significantly minimizes the number of false positives (FPs) when used in conjunction with computer aided detection (CAD) by eliminating non-correlated nodule candidates. Sixty-one low exposure posterior projections were acquired from more than 20 human subjects with small angular separations (0.32 degree) over a range of 20 degrees along the vertical axis. All patients were previously diagnosed for the presence of lung nodules based on computed tomography (CT) examination. Images were processed following two steps. First, all images were analyzed using our CAD routine for chest radiography. This process proceeded with a BCI processing in which the results of CAD on each single projection were examined in terms of their geometrical correlation with those found in the other 60 projections based on the predetermined shift of possible nodule locations in each projection. The suspect entities with a geometrical correlation that coincided with the known location of the lesions were selected as nodules; otherwise they were ignored. An expert radiologist with reference to the associated CT dataset determined the truth regarding nodule location and sizes, which were then used to determine if the found nodules are true positive or false positive. The preliminary results indicated that the best performance was obtained when the angular separation of the projection pair was greater than about 6.7 degrees. Within the range of optimum angular separation, the number of FPs per image was 0-1 without impacting the number of true positives (TPs), averaged around 92%. (Supported by grants from the NIH: R01-CA80490 and R01CA109074).

Authors
Nasab, NM; Samei, E; III, JTD
MLA Citation
Nasab, NM, Samei, E, and III, JTD. "Biplane correlation imaging for lung nodule detection: Initial human subject results." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6144 I (2006).
Source
scival
Published In
Proceedings of SPIE
Volume
6144 I
Publish Date
2006
DOI
10.1117/12.652582

Beam optimization for digital mammography - II

Optimization of acquisition technique factors (target, filter, and kVp) in digital mammography is required for maximization of the image SNR, while minimizing patient dose. The goal of this study is to compare, for each of the major commercially available FFDM systems, the effect of various technique factors on image SNR and radiation dose for a range of breast thickness and tissue types. This phantom study follows the approach of an earlier investigation[1], and includes measurements on recent versions of two of the FFDM systems discussed in that paper, as well as on three FFDM systems not available at that time, The five commercial FFDM systems tested are located at five different university test sites and include all FFDM systems that are currently FDA approved. Performance was assessed using 9 different phantom types (three compressed thicknesses, and three tissue composition types) using all available x-ray target and filter combinations, The figure of merit (FOM) used to compare technique factors is the ratio of the square of the image SNR to the mean glandular dose (MGD). This FOM has been used previously by others in mammographic beam optimization studies [2],[3]. For selected examples, data are presented describing the change in SNR, MOD, and FOM with changing kVp, as well as with changing target and/or filter type. For all nine breast types the target/filter/kVp combination resulting in the highest FOM value is presented. Our results suggest that in general, technique combinations resulting in higher energy beams resulted in higher FOM values, for nearly all breast types. © Springer-Verlag Berlin Heidelberg 2006.

Authors
Williams, MB; Raghunathan, P; Seibert, A; Kwan, A; Lo, J; Samei, E; Fajardo, L; Maidment, ADA; Yaffe, M; Bloomquist, A
MLA Citation
Williams, MB, Raghunathan, P, Seibert, A, Kwan, A, Lo, J, Samei, E, Fajardo, L, Maidment, ADA, Yaffe, M, and Bloomquist, A. "Beam optimization for digital mammography - II." Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) 4046 LNCS (2006): 273-280.
Source
scival
Published In
Lecture notes in computer science
Volume
4046 LNCS
Publish Date
2006
Start Page
273
End Page
280

In-field evaluation of the modulation transfer function and the signal-to-noise ratio of electronic-display devices

This paper describes a charged-coupled device (CCD) camera, which was developed for in-field evaluation of the image quality of electronic-display devices [such as cathode-ray tubes (CRTs) and liquid-crystal displays (LCDs)] used for medical applications. Contrary to traditional cameras for display-image-quality evaluation, this CCD camera does not require a sophisticated x-y-z translation stage for mounting and adjustment. Instead, it is handheld and pressed by gentle pressure against the display screen. It is controlled by a software package which was originally developed for display calibration according to the DICOM 14 gray-scale standard display function (CSDF).1 This software package controls the camera gain when measurements are made at different display luminance, display test patterns, performs image analysis and displays the results of the measurements and calculations. The work concentrated on the measurement of modulation transfer function (MTF) and of signal-to-noise ratio (SNR) per display pixel. The MTF is derived from the Fourier transform of the line spread function (LSF). The single-display-pixel SNR is derived from the integration of the noise power spectrum (NPS) of a camera image taken of a display with a uniform luminance. It is demonstrated that the device can produce repeatable results in terms of MTF and SNR. MTFs were measured on three monochrome CRTs and five monochrome LCDs in order to study repeatability and similar quantities. The MTF was measured on a 5-Mpixel LCD yielding values that lie within 3.5% of the average MTF at the Nyquist frequency and 4.0% of the maximum total sharpness (∫ MTF2 df). The MTF was also measured on a 9-Mpixel LCD, yielding values that lie within 9.0% of the average MTF at the Nyquist frequency and 8.0% of the maximum total sharpness. The SNR was measured eight times on a 3-Mpixel monochrome LCD at nine digital driving levels (DDLs). At a DDL of 185, the mean SNR was 15.694 and the standard deviation (Stdv) was 0.587. At a DDL of 65, the mean SNR was 5.675 and Stdv was 0.120. © Copyright 2006 Society for Information Display.

Authors
Roehrig, H; Gaskill, J; Fan, J; Martin, C; Greivenkamp, J; Samei, E
MLA Citation
Roehrig, H, Gaskill, J, Fan, J, Martin, C, Greivenkamp, J, and Samei, E. "In-field evaluation of the modulation transfer function and the signal-to-noise ratio of electronic-display devices." Journal of the Society for Information Display 14.10 (2006): 847-860.
Source
scival
Published In
Journal of the Society for Information Display
Volume
14
Issue
10
Publish Date
2006
Start Page
847
End Page
860
DOI
10.1889/1.2372418

Why Medical Image Perception?

Authors
Samei, E
MLA Citation
Samei, E. "Why Medical Image Perception?." Journal of the American College of Radiology 3.6 (2006): 400-401.
Source
scival
Published In
Journal of the American College of Radiology
Volume
3
Issue
6
Publish Date
2006
Start Page
400
End Page
401
DOI
10.1016/j.jacr.2006.02.017

Invited paper: Displaying your health: An overview of medical display research

Medical imaging has been moving from analog technologies (such as x-ray film) to digital ones in recent years. The quality of a digital image depends on the quality of the detector equipment used to capture the image, image processing applied to the image, and the medical display where the image is viewed. In light of the importance of the medical display, medical imaging research has begun to study the properties of these devices. This paper will explore physical measurements of several medical displays and examine how different displays affect diagnostic performance. © Copyright 2006 Society for Information Display.

Authors
Jr, RSS; Samei, E
MLA Citation
Jr, RSS, and Samei, E. "Invited paper: Displaying your health: An overview of medical display research." Proceedings of the Third Americas Display Engineering and Applications Conference, ADEAC 2006 2006 (2006): 35-37.
Source
scival
Published In
Proceedings of the Third Americas Display Engineering and Applications Conference, ADEAC 2006
Volume
2006
Publish Date
2006
Start Page
35
End Page
37

Erratum: Contrast-detail analysis of three flat panel detectors for digital radiography (Medical Physics (2006) 33, (1707-1719))

Authors
Borasi, G; Samei, E; Bertolini, M; Nitrosi, A; Tassoni, D
MLA Citation
Borasi, G, Samei, E, Bertolini, M, Nitrosi, A, and Tassoni, D. "Erratum: Contrast-detail analysis of three flat panel detectors for digital radiography (Medical Physics (2006) 33, (1707-1719))." Medical Physics 33.9 (2006): 3580--.
Source
scival
Published In
Medical physics
Volume
33
Issue
9
Publish Date
2006
Start Page
3580-
DOI
10.1118/1.2337636

A Monte Carlo investigation on the impact of scattered radiation on mammographic resolution and noise

Scattered radiation plays a significant role in mammographic imaging, with scatter fractions over 50% for larger, denser breasts. For screen-film systems, scatter primarily affects the image contrast, reducing the conspicuity of subtle lesions. While digital systems can overcome contrast degradation, they remain susceptible to scatter's impact on the image resolution and noise. To better understand this impact, we have created a Monte Carlo model of a mammographic imaging system adaptable for different imaging situations. This model flags primary and scatter photons and therefore can produce primary-only, scatter-only, or primary plus scatter images. Resolution was assessed using the edge technique to compute the Modulation Transfer Function (MTF). The MTF of a selenium detector imaged with a 28 kVp Mo/Mo beam filtered through a 6 cm heterogeneous breast was 0.81, 0.0002, and 0.65 at 5 mm -1 for the primary beam, scatter-only, and primary plus scatter beam, respectively. Noise was measured from flat-field images via the noise power spectrum (NNPS). The NNPS-exposure product using the same imaging conditions was 1.5-10 -5 mm 2·mR, 1.6-10 -5 mm 2·mR, and 1.9-10 -5 mm 2·mR at 5 mm -1 for the primary, scatter, and primary plus scatter beam, respectively. The results show that scatter led to a notable low-frequency drop in the MTF and an increased magnitude of the NNPS-exposure product. (This work was supported in part by USAMRMC W81XWH-04-1-0323.).

Authors
Jr, RSS; Samei, E
MLA Citation
Jr, RSS, and Samei, E. "A Monte Carlo investigation on the impact of scattered radiation on mammographic resolution and noise." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6142 II (2006).
Source
scival
Published In
Proceedings of SPIE
Volume
6142 II
Publish Date
2006
DOI
10.1117/12.653199

The impact of angular separation on the performance of biplane correlation imaging for lung nodule detection

In this paper, we evaluate the performance of biplane correlation imaging (BCI) using a set of off-angle projections acquired from an anthropomorphic chest phantom. BCI reduces the effect of anatomical noise, which would otherwise impact the detection subtle lesions in planar images. BCI also minimizes the number of false positives (FPs) when used in conjunction with computer aided diagnosis (CAD) applied to a set of coronal chest x-ray projections by eliminating non-correlated nodule candidates. In BCI, two digital images of the chest are acquired within a short time interval from two slightly different posterior projections. The image data are then incorporated into the CAD algorithm in which nodules are detected by examining the geometrical correlation of the detected signals in the two views, thus largely "canceling" the impact of anatomical noise. Seventy-one low exposure posterior projections were acquired of an anthropomorphic chest phantom containing tissue equivalent lesions with small angular separations (0.32 degree) over a range of 20 degrees, [-10°, +10°], along the vertical axis. The data were analyzed to determine the accuracy of the technique as a function of angular separation. The results indicated that the best performance was obtained when the angular separation of the projection pair was greater than 6 degrees. Within the range of optimum angular separation, the number of FPs per image, FPpI, was ∼1.1 with average sensitivity around 75% (supported by a grant from the NIH R01CA 109074).

Authors
Nasab, NM; Samei, E
MLA Citation
Nasab, NM, and Samei, E. "The impact of angular separation on the performance of biplane correlation imaging for lung nodule detection." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6142 I (2006).
Source
scival
Published In
Proceedings of SPIE
Volume
6142 I
Publish Date
2006
DOI
10.1117/12.652588

Performance evaluation of a commercial system for quantitative measurement of display resolution

One of the key metrics that carry information about image quality of medical displays is resolution. Until now, this property has been quantitatively assessed in laboratory settings. For the first time, a device consisting of a CCD camera and analysis software has been made commercially available for measuring the resolution of medical displays in a clinical setting. This study aimed to evaluate this new product in terms of accuracy and precision. In particular, attention was paid to determine whether the device is appropriate for clinical use. This work involved the measurement of the Modulation Transfer Function (MTF) of a medical Liquid Crystal Display (LCD) using the software/camera system. To check for accuracy, the results were compared with published values of the resolution for the same display. To assess the system's precision, measurements were made multiple times at the same setting. The performance of the system was also ascertained as a function of the focus setting of the camera. In terms of repeatability, the results indicate that when the camera is focused within ±0.64 mm of the optimum focus setting, the MTF values lie within approximately 14% of the best focus MTF at the Nyquist frequency and 11% of the optimum total sharpness (JMTF df). Similar results were obtained in the horizontal and vertical directions. Also, the MTF results track with luminance values as expected. In terms of accuracy, the device provides MTF figures within 10% to 20% of the previously measured values.

Authors
Cleland, EW; Samei, E
MLA Citation
Cleland, EW, and Samei, E. "Performance evaluation of a commercial system for quantitative measurement of display resolution." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6141 (2006).
Source
scival
Published In
Proceedings of SPIE
Volume
6141
Publish Date
2006
DOI
10.1117/12.655675

A method for reduction of eye fatigue by optimizing the ambient light conditions in radiology reading rooms

Ambient lighting in soft-copy reading rooms are currently kept at low values to preserve contrast rendition in the dark regions of a medical image. Low illuminance levels, however, create inadequate viewing conditions and may also cause eye-strain. This eye-strain may be attributed to notable variations in luminance adaptation state of the reader's eyes when moving the gaze intermittently between the brighter display and darker surrounding surfaces. This paper presents a methodology to optimize the lighting conditions of reading rooms to reduce visual fatigue by minimizing this variation by exploiting the properties of LCDs with low diffuse reflection coefficients and high luminance ratio. First, a computational model was developed to determine a global luminance adaptation value, L adp, when viewing a medical image on display. The model is based on the diameter of the pupil size which depends on the luminance of the observed object. Second, this value was compared with the luminance reflected off surrounding surfaces, L s, under various conditions of room illuminance, E, different values of diffuse reflection coefficients of surrounding surfaces, R s, and calibration settings of a typical LCD. The results suggest that for typical luminance settings of current LCDs, it is possible to raise ambient illumination to minimize differences in eye adaptation, potentially reducing visual fatigue while also complying with the TG18 specifications for controlled contrast rendition. Specifically, room illumination in the 75-150 lux range and surface diffuse reflection coefficients in the practical range of 0.13-0.22 sr -1 provide an ideal setup for typical LCDs. Furthermore, displays with lower diffuse reflectivity and with higher inherent luminance ratio than currently possible in most LCDs can potentially help further decrease eye fatigue, providing an improved ergonomic viewing conditions in reading rooms.

Authors
Chawla, AS; Samei, E
MLA Citation
Chawla, AS, and Samei, E. "A method for reduction of eye fatigue by optimizing the ambient light conditions in radiology reading rooms." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6145 (2006).
Source
scival
Published In
Proceedings of SPIE
Volume
6145
Publish Date
2006
DOI
10.1117/12.655688

X-ray tube voltage and image quality in adult and pediatric CT

The purpose of this study was to investigate how tissue x-ray attenuation coefficients, and their uncertainties, vary with x-ray tube voltage in different sized patients. Anthropomorphic phantoms (newborn, 10 year old, adult) were scanned a GE LightSpeed scanner at four x-ray tube voltages. Measurements were made of tissue attenuation in the head, chest and abdomen regions, as well as the corresponding noise values. Tissue signal to noise ratios (SNR) were obtained by dividing the average attenuation coefficient by the corresponding standard deviation. Soft tissue attenuation coefficients, relative to water, showed little variation with patient location or x-ray voltage (< 0.5%), but increasing the x-ray tube voltage from 80 to 140 kV reduced bone x-ray attenuation by ∼14%. All tissues except adult bone showed a reduction of noise with increasing x-ray tube voltage (kV); the noise was found to be proportional to kV and the average value of n for all tissues was -1.19 ±0.57. In pediatric patients at a constant x-ray tube voltage, SNR values were approximately independent of the body region, but the adult abdomen soft tissue SNR values were ∼40% lower than the adult head. SNR values in the newborn were more than double the corresponding SNR soft tissue values in adults. SNR values for lung and bone were generally lower than those for soft tissues. For soft tissues, increasing the x-ray tube voltage from 80 to 140 kV increased the SNR by an average of ∼90%. Data in this paper can be used to help design CT imaging protocols that take into account patient size and diagnostic imaging task.

Authors
Huda, W; Ogden, KM; Scalzetti, EM; Lavallee, RL; Samei, E
MLA Citation
Huda, W, Ogden, KM, Scalzetti, EM, Lavallee, RL, and Samei, E. "X-ray tube voltage and image quality in adult and pediatric CT." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6142 II (2006).
Source
scival
Published In
Proceedings of SPIE
Volume
6142 II
Publish Date
2006
DOI
10.1117/12.649279

Potential for lower absorbed dose in digital mammography: A JAFROC experiment using clinical hybrid images with simulated dose reduction

To determine how image quality linked to tumor detection is affected by reducing the absorbed dose to 50% and 30% of the clinical levels represented by an average glandular dose (AGO) level of 1.3 mGy for a standard breast according to European guidelines. Materials and methods: 90 normal, unprocessed images were acquired from the screening department using a full-field digital mammography (FFDM) unit Mammomat Novation (Siemens). Into 40 of these, one to three simulated tumors were inserted per image at various positions. These tumors represented irregular-shaped malignant masses. Dose reduction was simulated in all 90 images by adding simulated quantum noise to represent images acquired at 50% and 30% of the original dose, resulting in 270 images, which were subsequently processed for final display. Four radiologists participated in a free-response receiver operating characteristics (FROG) study in which they searched for and marked suspicious positions of the masses as well as rated their degree of suspicion of occurrence on a one to four scale. Using the jackknife FROG (JAFROC) method, a score between 0 and 1 (where 1 represents best performance), referred to as a figure-of-merit (FOM), was calculated for each dose level. Results: The FOM was 0.73, 0.70, and 0.68 for the 100%, 50% and 30% dose levels, respectively. Using Analysis of the Variance (ANOVA) to test for statistically significant differences between any two of the three FOMs revealed that they were not statistically distinguishable (p-value of 0.26). Conclusion: For the masses used in this experiment, there was no significant change in detection by increasing quantum noise, thus indicating a potential for dose reduction.

Authors
Timberg, P; Ruschin, M; Båth, M; Hemdal, B; Andersson, I; Mattsson, S; Chakraborty, D; Saunders, R; Samei, E; Tingberg, A
MLA Citation
Timberg, P, Ruschin, M, Båth, M, Hemdal, B, Andersson, I, Mattsson, S, Chakraborty, D, Saunders, R, Samei, E, and Tingberg, A. "Potential for lower absorbed dose in digital mammography: A JAFROC experiment using clinical hybrid images with simulated dose reduction." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6146 (2006).
Source
scival
Published In
Proceedings of SPIE
Volume
6146
Publish Date
2006
DOI
10.1117/12.653419

Analyzing the Effect of dose reduction on the detection of mammographic lesions using mathematical observer models

The purpose of this study was to determine the effect of dose reduction on the detectability of breast lesions in mammograms. Mammograms with dose levels corresponding to 50% and 25% of the original clinically-relevant exposure levels were simulated. Detection of masses and microcalicifications embedded in these mammograms was analyzed by four mathematical observer models, namely, the Hotelling Observer, Non-prewhitening Matched Filter with Eye Filter (NPWE), and Laguerre-Gauss and Gabor Channelized Hotelling Observers. Performance was measured in terms of ROC curves and Area under ROC Curves (AUC) under Signal Known Exactly but Variable Tasks (SKEV) paradigm. Gabor Channelized Hotelling Observer predicted deterioration in detectability of benign masses. The other algorithmic observers, however, did not indicate statistically significant differences in the detectability of masses and microcalcifications with reduction in dose. Detection of microcalcifications was affected more than the detection of masses. Overall, the results indicate that there is a potential for reduction of radiation dose level in mammographic screening procedures without severely compromising the detectability of lesions.

Authors
Chawla, AS; Saunders, R; Abbey, C; Delong, D; Samei, E
MLA Citation
Chawla, AS, Saunders, R, Abbey, C, Delong, D, and Samei, E. "Analyzing the Effect of dose reduction on the detection of mammographic lesions using mathematical observer models." Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6146 (2006).
Source
scival
Published In
Proceedings of SPIE
Volume
6146
Publish Date
2006
DOI
10.1117/12.656378

Combined SPECT/CT imaging onboard radiation-therapy machines: A comparison of flat-panel and anger-camera systems

Authors
Bowsher, JE; Yin, F; Chawla, AS; Greer, KL; Jaszczak, RJ; Samei, E; Willett, CG
MLA Citation
Bowsher, JE, Yin, F, Chawla, AS, Greer, KL, Jaszczak, RJ, Samei, E, and Willett, CG. "Combined SPECT/CT imaging onboard radiation-therapy machines: A comparison of flat-panel and anger-camera systems." 2006.
Source
wos-lite
Published In
International Journal of Radiation Oncology, Biology, Physics
Volume
66
Issue
3
Publish Date
2006
Start Page
S147
End Page
S148
DOI
10.1016/j.ijrobp.2006.07.297

The nature of the digital image

Authors
Samei, E; Jr, SRS
MLA Citation
Samei, E, and Jr, SRS. "The nature of the digital image." 2006.
Source
wos-lite
Published In
Medical physics monograph
Issue
30
Publish Date
2006
Start Page
103
End Page
123

Initial study of quasi-monochromatic X-ray beam performance for X-ray computed mammotomography

Authors
McKinley, RL; Tornai, MP; Samei, E; Bradshaw, ML
MLA Citation
McKinley, RL, Tornai, MP, Samei, E, and Bradshaw, ML. "Initial study of quasi-monochromatic X-ray beam performance for X-ray computed mammotomography." IEEE TRANSACTIONS ON NUCLEAR SCIENCE 52.5 (October 2005): 1243-1250.
Source
wos-lite
Published In
IEEE Transactions on Nuclear Science
Volume
52
Issue
5
Publish Date
2005
Start Page
1243
End Page
1250
DOI
10.1109/TNS.2005.0857629

Comparison of edge analysis techniques for the determination of the MTF of digital radiographic systems.

The modulation transfer function (MTF) is well established as a metric to characterize the resolution performance of a digital radiographic system. Implemented by various laboratories, the edge technique is currently the most widespread approach to measure the MTF. However, there can be differences in the results attributed to differences in the analysis technique employed. The objective of this study was to determine whether comparable results can be obtained from different algorithms processing identical images representative of those of current digital radiographic systems. Five laboratories participated in a round-robin evaluation of six different algorithms including one prescribed in the International Electrotechnical Commission (IEC) 62220-1 standard. The algorithms were applied to two synthetic and 12 real edge images from different digital radiographic systems including CR, and direct- and indirect-conversion detector systems.