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Song, Allen Wuming

Overview:

The research in our lab is concerned with advancing structural and functional MRI methodologies (e.g. fast and high-resolution imaging techniques) for human brain imaging. We also aim to improve our understanding of functional brain signals, including spatiotemporal characterizations of the blood oxygenation level dependent contrast and alternative contrast mechanisms that are more directly linked to the neuronal activities. Additional effort is invested in applying and validating the developed methods to study human functional neuroanatomy.

Positions:

Professor in Radiology

Radiology
School of Medicine

Professor of Biomedical Engineering

Biomedical Engineering
Pratt School of Engineering

Professor in Neurobiology

Neurobiology
School of Medicine

Professor in Psychiatry and Behavioral Sciences

Psychiatry & Behavioral Sciences
School of Medicine

Faculty Network Member of the Duke Institute for Brain Sciences

Duke Institute for Brain Sciences
Institutes and Provost's Academic Units

Member of the Duke Cancer Institute

Duke Cancer Institute
School of Medicine

Director of the Center for Brain Imaging and Analysis

Duke-UNC Center for Brain Imaging and Analysis
School of Medicine

Education:

Ph.D. 1995

Ph.D. — Medical College of Wisconsin

News:

Grants:

Whole Eye Optical Coherence Tomography to Improve Refractive Surgery and Eye Care

Administered By
Ophthalmology
AwardedBy
National Institutes of Health
Role
Collaborator
Start Date
December 01, 2014
End Date
November 30, 2019

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

Integrated RF/shim body coil array for MRI with localized shimming

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Co Investigator
Start Date
April 01, 2017
End Date
January 31, 2019

High Resolution Intracortical DTI for Early Detection of Alzheimer¿s Disease

Administered By
Radiology, Neuroradiology
AwardedBy
Neuroradiology Education and Reserach Foundation (formerly Foundation of the ASNR)
Role
Collaborator
Start Date
October 01, 2016
End Date
September 30, 2018

Integrated Parallel Reception, Excitation, and Bo Shimming

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
GE Healthcare
Role
Principal Investigator
Start Date
September 01, 2016
End Date
September 30, 2018

Magnetic resonance imaging with inherent local shimming

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
April 01, 2015
End Date
January 31, 2018

High Fidelity Diffusion MRI for Children with Cerebral Palsy in Stem Cell Therapy

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
February 15, 2012
End Date
January 31, 2018

MRI & Data Analysis Services for MIRECC

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
Durham Veterans Affairs Medical Center
Role
Principal Investigator
Start Date
October 01, 2015
End Date
September 30, 2017

Oncogenic Signaling Networks

Administered By
Surgery, Surgical Sciences
AwardedBy
Department of Defense
Role
Co Investigator
Start Date
September 30, 2012
End Date
September 29, 2017

High-Resolution Diffusion Weighted MRI

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
General Electric Company
Role
Principal Investigator
Start Date
September 01, 2014
End Date
August 31, 2017

Path Toward MRI with Direct Sensitivity to Neuro-Electro-Magnetic Oscillations

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
September 26, 2014
End Date
June 30, 2017

Motion-immune neuro and body MRI for challenging patient populations

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Collaborator
Start Date
September 24, 2014
End Date
June 30, 2017

Imaging of Intrinsic Connectivity Networks

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Co Investigator
Start Date
September 30, 2011
End Date
June 30, 2017

FAST- MAS Phase 2A

Administered By
Duke Clinical Research Institute
AwardedBy
National Institutes of Health
Role
Co Investigator
Start Date
August 29, 2013
End Date
June 28, 2017

Neural circuits that regulate social motivation

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
University of North Carolina - Chapel Hill
Role
Principal Investigator
Start Date
September 24, 2013
End Date
May 31, 2017

Neuroimaging of Visual Attention in Aging

Administered By
Psychiatry & Behavioral Sciences, Geriatric Behavioral Health
AwardedBy
National Institutes of Health
Role
Advisor
Start Date
September 01, 2011
End Date
May 31, 2017

Attentional Mechanisms in Multisensory Environments

Administered By
Center for Cognitive Neuroscience
AwardedBy
National Institutes of Health
Role
Co Investigator
Start Date
January 01, 2006
End Date
May 31, 2017

Consequences of prolonged febrile seizures in childhood

Administered By
Pediatrics, Neurology
AwardedBy
Albert Einstein College of Medicine
Role
Co Investigator
Start Date
May 01, 2013
End Date
April 30, 2017

A Compute Cluster for Brain Imaging and Analysis

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
April 01, 2016
End Date
March 31, 2017

Susceptibility MRI as a marker for diagnosis and clinical disability in MS

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Co Investigator
Start Date
September 30, 2014
End Date
February 28, 2017

High-resolution in vivo and non-invasive imaging of myocardial fibers

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Co Investigator
Start Date
May 01, 2014
End Date
June 30, 2016

Pathways From Maltreatment to Substance Abuse

Administered By
Psychiatry, Child & Family Mental Health and Developmental Neuroscience
AwardedBy
National Institutes of Health
Role
Collaborator
Start Date
May 01, 2010
End Date
April 30, 2016

Restricted Repetitive Behavior in Autism

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
University of North Carolina - Chapel Hill
Role
Principal Investigator
Start Date
June 01, 2011
End Date
March 31, 2016

Direct MRI of Neuroelectric Activity for Animal Neuroimaging

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Co Investigator
Start Date
February 01, 2011
End Date
January 31, 2016

Imaging Genetic Predictors of Psychotherapy Outcomes in Unipolar Depression

Administered By
Psychiatry & Behavioral Sciences, Translational Neuroscience
AwardedBy
National Institutes of Health
Role
Collaborator
Start Date
April 06, 2012
End Date
May 31, 2015

Neuroimaging of Age-Related Changes in Language

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Collaborator
Start Date
May 01, 2010
End Date
April 30, 2015

Magnetic Resonance Imaging of Cortical Neuronal Activity

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
July 01, 2010
End Date
March 31, 2015

Studies of Attention Using Combined ERPs and fMRI

Administered By
Center for Cognitive Neuroscience
AwardedBy
National Institutes of Health
Role
Co Investigator
Start Date
April 05, 2001
End Date
January 31, 2015

Network Plasticity in Pediatric Traumatic Brain Injury

Administered By
Pediatrics, Neurology
AwardedBy
Child Neurology Foundation
Role
Mentor
Start Date
January 01, 2013
End Date
December 31, 2014

Environments as Smoking Cues: Imaging Brain Substrates, Developing New Treatments

Administered By
Psychiatry & Behavioral Sciences, Addictions
AwardedBy
National Institutes of Health
Role
Co Investigator
Start Date
July 15, 2012
End Date
December 30, 2014

Cross-disciplinary Training in Medical Physics

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

Longitudinal Functional Imaging of Early Childhood Anxiety Disorders

Administered By
Psychiatry, Child & Family Mental Health and Developmental Neuroscience
AwardedBy
National Institutes of Health
Role
Co Investigator
Start Date
May 02, 2008
End Date
April 30, 2013

High Resolution Diffusion-Weighted Magnetic Resonance Imaging at 300-Micron Level

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Advisor
Start Date
December 01, 2006
End Date
December 31, 2012

Human Functional Brain Anatomy

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
September 30, 2001
End Date
August 31, 2012

Myelin-Specific Diffusion Tensor Imaging for Developmental Neuroimaging

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
June 01, 2009
End Date
May 31, 2012

Neural correlates of working memory in children with 22q11.2 deletion syndrome

Administered By
Pediatrics, Medical Genetics
AwardedBy
National Institutes of Health
Role
Mentor
Start Date
September 24, 2010
End Date
November 23, 2011

Precision Targeting of fMRI-Guided TMS Using a Robotic Arm System

Administered By
Psychiatry & Behavioral Sciences, Brain Stimulation and Neurophysiology
AwardedBy
National Institutes of Health
Role
Investigator
Start Date
June 15, 2010
End Date
June 14, 2011

Multisensory Processing and Attention

Administered By
Center for Cognitive Neuroscience
AwardedBy
National Science Foundation
Role
Co Investigator
Start Date
September 01, 2005
End Date
August 31, 2010

K-Space Energy Spectrum Analysis for Echo-Planar Imaging

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Advisor
Start Date
November 01, 2007
End Date
June 30, 2010

Direct MRI of Neuroelectric Activity

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Science Foundation
Role
Principal Investigator
Start Date
May 15, 2006
End Date
April 30, 2010

A Linux Cluster Computational Facility for Neuroimaging Research

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
April 01, 2009
End Date
March 31, 2010

High Fidelity fMRI

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
May 15, 2004
End Date
February 28, 2010

IPA - Francis Favorini

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
Veterans Administration Medical Center
Role
Principal Investigator
Start Date
July 01, 2007
End Date
June 30, 2009

Neuroimaging of Executive Processing

Administered By
Center for Cognitive Neuroscience
AwardedBy
National Institutes of Health
Role
Co Investigator
Start Date
January 01, 2005
End Date
June 30, 2009

Neuroimaging Attentional Impairment During Abstinence

Administered By
Psychiatry & Behavioral Sciences, Addictions
AwardedBy
National Institutes of Health
Role
Consultant
Start Date
July 01, 2004
End Date
June 30, 2009

IPA - Jacquelynn Price

Administered By
Duke-UNC Center for Brain Imaging and Analysis
AwardedBy
Veterans Administration Medical Center
Role
Principal Investigator
Start Date
March 01, 2006
End Date
February 29, 2008

Spatiotemporal Dynamics of Emotional Memory Networks

Administered By
Center for Cognitive Neuroscience
AwardedBy
National Institutes of Health
Role
Co Investigator
Start Date
April 01, 2001
End Date
March 31, 2007

Improved Image Acquisition for Functional Magnetic Resonance Imaging

Administered By
Radiology, Musculoskeletal Imaging
AwardedBy
National Science Foundation
Role
Principal Investigator
Start Date
April 01, 2001
End Date
March 31, 2006

Combined PET and ERP Studies of Selective Attention

Administered By
Center for Cognitive Neuroscience
AwardedBy
National Institute of Mental Health (NIMH)
Role
Co-Principal Investigator
Start Date
April 01, 1997
End Date
March 31, 2000
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Publications:

Phase-updated regularized SENSE for navigator-free multishot diffusion imaging.

Either SENSE+CG or POCS-ICE methods can be used to correct for motion-induced phase errors in navigator-free multishot diffusion imaging. SENSE+CG has the advantage of a fast convergence, however, occasionally the convergence can be unstable, thus degrading the image quality. POCS-ICE has a stable convergence and can be used with a high number of shots, but its convergence is slow, which limits its practical usage. The study here proposes an improved method based on both SENSE+CG and POCS-ICE, called Phase-updated Regularized SENSE (PR-SENSE), for navigator-free multishot diffusion imaging.In PR-SENSE, a total variation regularization method is used to solve the SENSE inverse problem instead of the conjugate gradient method used in SENSE+CG. This method is implemented by using a lagged diffusivity fixed point iteration algorithm. Additionally, the phase is updated during the iteration process to improve the image accuracy.Simulations and in vivo experiments demonstrated that PR-SENSE can successfully correct for the motion-induced phase errors in multi-shot DWI. It integrates the advantages of SENSE+CG and POCS-ICE, resulting in a fast and stable convergence with improved image quality.Given its advantages, PR-SENSE is a significant improvement over other methods for navigator-free high-resolution DWI. Magn Reson Med, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

Authors
Hu, Z; Ma, X; Truong, T-K; Song, AW; Guo, H
MLA Citation
Hu, Z, Ma, X, Truong, T-K, Song, AW, and Guo, H. "Phase-updated regularized SENSE for navigator-free multishot diffusion imaging." Magnetic resonance in medicine (August 13, 2016).
PMID
27520840
Source
epmc
Published In
Magnetic Resonance in Medicine
Publish Date
2016
DOI
10.1002/mrm.26361

Motion immune diffusion imaging using augmented MUSE for high-resolution multi-shot EPI.

To develop new techniques for reducing the effects of microscopic and macroscopic patient motion in diffusion imaging acquired with high-resolution multishot echo-planar imaging.The previously reported multiplexed sensitivity encoding (MUSE) algorithm is extended to account for macroscopic pixel misregistrations, as well as motion-induced phase errors in a technique called augmented MUSE (AMUSE). Furthermore, to obtain more accurate quantitative diffusion-tensor imaging measures in the presence of subject motion, we also account for the altered diffusion encoding among shots arising from macroscopic motion.MUSE and AMUSE were evaluated on simulated and in vivo motion-corrupted multishot diffusion data. Evaluations were made both on the resulting imaging quality and estimated diffusion tensor metrics.AMUSE was found to reduce image blurring resulting from macroscopic subject motion compared to MUSE but yielded inaccurate tensor estimations when neglecting the altered diffusion encoding. Including the altered diffusion encoding in AMUSE produced better estimations of diffusion tensors.The use of AMUSE allows for improved image quality and diffusion tensor accuracy in the presence of macroscopic subject motion during multishot diffusion imaging. These techniques should facilitate future high-resolution diffusion imaging.

Authors
Guhaniyogi, S; Chu, M-L; Chang, H-C; Song, AW; Chen, N-K
MLA Citation
Guhaniyogi, S, Chu, M-L, Chang, H-C, Song, AW, and Chen, N-K. "Motion immune diffusion imaging using augmented MUSE for high-resolution multi-shot EPI." Magnetic resonance in medicine 75.2 (February 2016): 639-652.
PMID
25762216
Source
epmc
Published In
Magnetic Resonance in Medicine
Volume
75
Issue
2
Publish Date
2016
Start Page
639
End Page
652
DOI
10.1002/mrm.25624

Human brain diffusion tensor imaging at submillimeter isotropic resolution on a 3Tesla clinical MRI scanner.

The advantages of high-resolution diffusion tensor imaging (DTI) have been demonstrated in a recent post-mortem human brain study (Miller et al., NeuroImage 2011;57(1):167-181), showing that white matter fiber tracts can be much more accurately detected in data at a submillimeter isotropic resolution. To our knowledge, in vivo human brain DTI at a submillimeter isotropic resolution has not been routinely achieved yet because of the difficulty in simultaneously achieving high resolution and high signal-to-noise ratio (SNR) in DTI scans. Here we report a 3D multi-slab interleaved EPI acquisition integrated with multiplexed sensitivity encoded (MUSE) reconstruction, to achieve high-quality, high-SNR and submillimeter isotropic resolution (0.85×0.85×0.85mm(3)) in vivo human brain DTI on a 3Tesla clinical MRI scanner. In agreement with the previously reported post-mortem human brain DTI study, our in vivo data show that the structural connectivity networks of human brains can be mapped more accurately and completely with high-resolution DTI as compared with conventional DTI (e.g., 2×2×2mm(3)).

Authors
Chang, H-C; Sundman, M; Petit, L; Guhaniyogi, S; Chu, M-L; Petty, C; Song, AW; Chen, N-K
MLA Citation
Chang, H-C, Sundman, M, Petit, L, Guhaniyogi, S, Chu, M-L, Petty, C, Song, AW, and Chen, N-K. "Human brain diffusion tensor imaging at submillimeter isotropic resolution on a 3Tesla clinical MRI scanner." NeuroImage 118 (September 2015): 667-675.
PMID
26072250
Source
epmc
Published In
NeuroImage
Volume
118
Publish Date
2015
Start Page
667
End Page
675
DOI
10.1016/j.neuroimage.2015.06.016

Effects of repetitive transcranial magnetic stimulation on motor symptoms in Parkinson disease: a systematic review and meta-analysis.

Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive neuromodulation technique that has been closely examined as a possible treatment for Parkinson disease (PD). However, results evaluating the effectiveness of rTMS in PD are mixed, mostly owing to low statistical power or variety in individual rTMS protocols.To determine the rTMS effects on motor dysfunction in patients with PD and to examine potential factors that modulate the rTMS effects.Databases searched included PubMed, EMBASE, Web of Knowledge, Scopus, and the Cochrane Library from inception to June 30, 2014.Eligible studies included sham-controlled, randomized clinical trials of rTMS intervention for motor dysfunction in patients with PD.Relevant measures were extracted independently by 2 investigators. Standardized mean differences (SMDs) were calculated with random-effects models.Motor examination of the Unified Parkinson's Disease Rating Scale.Twenty studies with a total of 470 patients were included. Random-effects analysis revealed a pooled SMD of 0.46 (95% CI, 0.29-0.64), indicating an overall medium effect size favoring active rTMS over sham rTMS in the reduction of motor symptoms (P<.001). Subgroup analysis showed that the effect sizes estimated from high-frequency rTMS targeting the primary motor cortex (SMD, 0.77; 95% CI, 0.46-1.08; P<.001) and low-frequency rTMS applied over other frontal regions (SMD, 0.50; 95% CI, 0.13-0.87; P=.008) were significant. The effect sizes obtained from the other 2 combinations of rTMS frequency and rTMS site (ie, high-frequency rTMS at other frontal regions: SMD, 0.23; 95% CI, -0.02 to 0.48, and low primary motor cortex: SMD, 0.28; 95% CI, -0.23 to 0.78) were not significant. Meta-regression revealed that a greater number of pulses per session or across sessions is associated with larger rTMS effects. Using the Grading of Recommendations, Assessment, Development, and Evaluation criteria, we characterized the quality of evidence presented in this meta-analysis as moderate quality.The pooled evidence suggests that rTMS improves motor symptoms for patients with PD. Combinations of rTMS site and frequency as well as the number of rTMS pulses are key modulators of rTMS effects. The findings of our meta-analysis may guide treatment decisions and inform future research.

Authors
Chou, Y-H; Hickey, PT; Sundman, M; Song, AW; Chen, N-K
MLA Citation
Chou, Y-H, Hickey, PT, Sundman, M, Song, AW, and Chen, N-K. "Effects of repetitive transcranial magnetic stimulation on motor symptoms in Parkinson disease: a systematic review and meta-analysis." JAMA neurology 72.4 (April 2015): 432-440. (Review)
PMID
25686212
Source
epmc
Published In
JAMA Neurology
Volume
72
Issue
4
Publish Date
2015
Start Page
432
End Page
440
DOI
10.1001/jamaneurol.2014.4380

Preschool anxiety disorders predict different patterns of amygdala-prefrontal connectivity at school-age.

In this prospective, longitudinal study of young children, we examined whether a history of preschool generalized anxiety, separation anxiety, and/or social phobia is associated with amygdala-prefrontal dysregulation at school-age. As an exploratory analysis, we investigated whether distinct anxiety disorders differ in the patterns of this amygdala-prefrontal dysregulation.Participants were children taking part in a 5-year study of early childhood brain development and anxiety disorders. Preschool symptoms of generalized anxiety, separation anxiety, and social phobia were assessed with the Preschool Age Psychiatric Assessment (PAPA) in the first wave of the study when the children were between 2 and 5 years old. The PAPA was repeated at age 6. We conducted functional MRIs when the children were 5.5 to 9.5 year old to assess neural responses to viewing of angry and fearful faces.A history of preschool social phobia predicted less school-age functional connectivity between the amygdala and the ventral prefrontal cortices to angry faces. Preschool generalized anxiety predicted less functional connectivity between the amygdala and dorsal prefrontal cortices in response to fearful faces. Finally, a history of preschool separation anxiety predicted less school-age functional connectivity between the amygdala and the ventral prefrontal cortices to angry faces and greater school-age functional connectivity between the amygdala and dorsal prefrontal cortices to angry faces.Our results suggest that there are enduring neurobiological effects associated with a history of preschool anxiety, which occur over-and-above the effect of subsequent emotional symptoms. Our results also provide preliminary evidence for the neurobiological differentiation of specific preschool anxiety disorders.

Authors
Carpenter, KLH; Angold, A; Chen, N-K; Copeland, WE; Gaur, P; Pelphrey, K; Song, AW; Egger, HL
MLA Citation
Carpenter, KLH, Angold, A, Chen, N-K, Copeland, WE, Gaur, P, Pelphrey, K, Song, AW, and Egger, HL. "Preschool anxiety disorders predict different patterns of amygdala-prefrontal connectivity at school-age." PloS one 10.1 (January 27, 2015): e0116854-.
Website
http://hdl.handle.net/10161/9486
PMID
25625285
Source
epmc
Published In
PloS one
Volume
10
Issue
1
Publish Date
2015
Start Page
e0116854
DOI
10.1371/journal.pone.0116854

Brain structural connectivity increases concurrent with functional improvement: evidence from diffusion tensor MRI in children with cerebral palsy during therapy.

Cerebral Palsy (CP) refers to a heterogeneous group of permanent but non-progressive movement disorders caused by injury to the developing fetal or infant brain (Bax et al., 2005). Because of its serious long-term consequences, effective interventions that can help improve motor function, independence, and quality of life are critically needed. Our ongoing longitudinal clinical trial to treat children with CP is specifically designed to meet this challenge. To maximize the potential for functional improvement, all children in this trial received autologous cord blood transfusions (with order randomized with a placebo administration over 2 years) in conjunction with more standard physical and occupational therapies. As a part of this trial, magnetic resonance imaging (MRI) is used to improve our understanding of how these interventions affect brain development, and to develop biomarkers of treatment efficacy. In this report, diffusion tensor imaging (DTI) and subsequent brain connectome analyses were performed in a subset of children enrolled in the clinical trial (n = 17), who all exhibited positive but varying degrees of functional improvement over the first 2-year period of the study. Strong correlations between increases in white matter (WM) connectivity and functional improvement were demonstrated; however no significant relationships between either of these factors with the age of the child at time of enrollment were identified. Thus, our data indicate that increases in brain connectivity reflect improved functional abilities in children with CP. In future work, this potential biomarker can be used to help differentiate the underlying mechanisms of functional improvement, as well as to identify treatments that can best facilitate functional improvement upon un-blinding of the timing of autologous cord blood transfusions at the completion of this study.

Authors
Englander, ZA; Sun, J; Laura Case, ; Mikati, MA; Kurtzberg, J; Song, AW
MLA Citation
Englander, ZA, Sun, J, Laura Case, , Mikati, MA, Kurtzberg, J, and Song, AW. "Brain structural connectivity increases concurrent with functional improvement: evidence from diffusion tensor MRI in children with cerebral palsy during therapy." NeuroImage. Clinical 7 (January 9, 2015): 315-324.
PMID
25610796
Source
epmc
Published In
NeuroImage: Clinical
Volume
7
Publish Date
2015
Start Page
315
End Page
324
DOI
10.1016/j.nicl.2015.01.002

Association between increased magnetic susceptibility of deep gray matter nuclei and decreased motor function in healthy adults.

In the human brain, iron is more prevalent in gray matter than in white matter, and deep gray matter structures, particularly the globus pallidus, putamen, caudate nucleus, substantia nigra, red nucleus, and dentate nucleus, exhibit especially high iron content. Abnormally elevated iron levels have been found in various neurodegenerative diseases. Additionally, iron overload and related neurodegeneration may also occur during aging, but the functional consequences are not clear. In this study, we explored the correlation between magnetic susceptibility--a surrogate marker of brain iron--of these gray matter structures with behavioral measures of motor and cognitive abilities, in 132 healthy adults aged 40-83 years. Latent variables corresponding to manual dexterity and executive functions were obtained using factor analysis. The factor scores for manual dexterity declined significantly with increasing age. Independent of gender, age, and global cognitive function, increasing magnetic susceptibility in the globus pallidus and red nuclei was associated with decreasing manual dexterity. This finding suggests the potential value of magnetic susceptibility, a non-invasive quantitative imaging marker of iron, for the study of iron-related brain function changes.

Authors
Li, W; Langkammer, C; Chou, Y-H; Petrovic, K; Schmidt, R; Song, AW; Madden, DJ; Ropele, S; Liu, C
MLA Citation
Li, W, Langkammer, C, Chou, Y-H, Petrovic, K, Schmidt, R, Song, AW, Madden, DJ, Ropele, S, and Liu, C. "Association between increased magnetic susceptibility of deep gray matter nuclei and decreased motor function in healthy adults." NeuroImage 105 (January 2015): 45-52.
PMID
25315786
Source
epmc
Published In
NeuroImage
Volume
105
Publish Date
2015
Start Page
45
End Page
52
DOI
10.1016/j.neuroimage.2014.10.009

Correction for Eddy Current-Induced Echo-Shifting Effect in Partial-Fourier Diffusion Tensor Imaging.

In most diffusion tensor imaging (DTI) studies, images are acquired with either a partial-Fourier or a parallel partial-Fourier echo-planar imaging (EPI) sequence, in order to shorten the echo time and increase the signal-to-noise ratio (SNR). However, eddy currents induced by the diffusion-sensitizing gradients can often lead to a shift of the echo in k-space, resulting in three distinct types of artifacts in partial-Fourier DTI. Here, we present an improved DTI acquisition and reconstruction scheme, capable of generating high-quality and high-SNR DTI data without eddy current-induced artifacts. This new scheme consists of three components, respectively, addressing the three distinct types of artifacts. First, a k-space energy-anchored DTI sequence is designed to recover eddy current-induced signal loss (i.e., Type 1 artifact). Second, a multischeme partial-Fourier reconstruction is used to eliminate artificial signal elevation (i.e., Type 2 artifact) associated with the conventional partial-Fourier reconstruction. Third, a signal intensity correction is applied to remove artificial signal modulations due to eddy current-induced erroneous T2(∗) -weighting (i.e., Type 3 artifact). These systematic improvements will greatly increase the consistency and accuracy of DTI measurements, expanding the utility of DTI in translational applications where quantitative robustness is much needed.

Authors
Truong, T-K; Song, AW; Chen, N-K
MLA Citation
Truong, T-K, Song, AW, and Chen, N-K. "Correction for Eddy Current-Induced Echo-Shifting Effect in Partial-Fourier Diffusion Tensor Imaging." BioMed research international 2015 (January 2015): 185026-.
Website
http://hdl.handle.net/10161/11994
PMID
26413505
Source
epmc
Published In
BioMed Research International
Volume
2015
Publish Date
2015
Start Page
185026
DOI
10.1155/2015/185026

Integrated RF/shim coil array for parallel reception and localized B0 shimming in the human brain.

The purpose of this work was to develop a novel integrated radiofrequency and shim (RF/shim) coil array that can perform parallel reception and localized B0 shimming in the human brain with the same coils, thereby maximizing both the signal-to-noise ratio and shimming efficiency. A 32-channel receive-only head coil array was modified to enable both RF currents (for signal reception) and direct currents (for B0 shimming) to flow in individual coil elements. Its in vivo performance was assessed in the frontal brain region, which is affected by large susceptibility-induced B0 inhomogeneities. The coil modifications did not reduce their quality factor or signal-to-noise ratio. Axial B0 maps and echo-planar images acquired in vivo with direct currents optimized to shim specific slices showed substantially reduced B0 inhomogeneities and image distortions in the frontal brain region. The B0 root-mean-square error in the anterior half of the brain was reduced by 60.3% as compared to that obtained with second-order spherical harmonic shimming. These results demonstrate that the integrated RF/shim coil array can perform parallel reception and localized B0 shimming in the human brain and provide a much more effective shimming than conventional spherical harmonic shimming alone, without taking up additional space in the magnet bore and without compromising the signal-to-noise ratio or shimming performance.

Authors
Truong, T-K; Darnell, D; Song, AW
MLA Citation
Truong, T-K, Darnell, D, and Song, AW. "Integrated RF/shim coil array for parallel reception and localized B0 shimming in the human brain." NeuroImage 103 (December 2014): 235-240.
PMID
25270602
Source
epmc
Published In
NeuroImage
Volume
103
Publish Date
2014
Start Page
235
End Page
240
DOI
10.1016/j.neuroimage.2014.09.052

Improved delineation of short cortical association fibers and gray/white matter boundary using whole-brain three-dimensional diffusion tensor imaging at submillimeter spatial resolution.

Recent emergence of human connectome imaging has led to a high demand on angular and spatial resolutions for diffusion magnetic resonance imaging (MRI). While there have been significant growths in high angular resolution diffusion imaging, the improvement in spatial resolution is still limited due to a number of technical challenges, such as the low signal-to-noise ratio and high motion artifacts. As a result, the benefit of a high spatial resolution in the whole-brain connectome imaging has not been fully evaluated in vivo. In this brief report, the impact of spatial resolution was assessed in a newly acquired whole-brain three-dimensional diffusion tensor imaging data set with an isotropic spatial resolution of 0.85 mm. It was found that the delineation of short cortical association fibers is drastically improved as well as the definition of fiber pathway endings into the gray/white matter boundary-both of which will help construct a more accurate structural map of the human brain connectome.

Authors
Song, AW; Chang, H-C; Petty, C; Guidon, A; Chen, N-K
MLA Citation
Song, AW, Chang, H-C, Petty, C, Guidon, A, and Chen, N-K. "Improved delineation of short cortical association fibers and gray/white matter boundary using whole-brain three-dimensional diffusion tensor imaging at submillimeter spatial resolution." Brain connectivity 4.9 (November 2014): 636-640.
Website
http://hdl.handle.net/10161/9461
PMID
25264168
Source
epmc
Published In
Brain Connectivity
Volume
4
Issue
9
Publish Date
2014
Start Page
636
End Page
640
DOI
10.1089/brain.2014.0270

Differential developmental trajectories of magnetic susceptibility in human brain gray and white matter over the lifespan.

As indicated by several recent studies, magnetic susceptibility of the brain is influenced mainly by myelin in the white matter and by iron deposits in the deep nuclei. Myelination and iron deposition in the brain evolve both spatially and temporally. This evolution reflects an important characteristic of normal brain development and ageing. In this study, we assessed the changes of regional susceptibility in the human brain in vivo by examining the developmental and ageing process from 1 to 83 years of age. The evolution of magnetic susceptibility over this lifespan was found to display differential trajectories between the gray and the white matter. In both cortical and subcortical white matter, an initial decrease followed by a subsequent increase in magnetic susceptibility was observed, which could be fitted by a Poisson curve. In the gray matter, including the cortical gray matter and the iron-rich deep nuclei, magnetic susceptibility displayed a monotonic increase that can be described by an exponential growth. The rate of change varied according to functional and anatomical regions of the brain. For the brain nuclei, the age-related changes of susceptibility were in good agreement with the findings from R2* measurement. Our results suggest that magnetic susceptibility may provide valuable information regarding the spatial and temporal patterns of brain myelination and iron deposition during brain maturation and ageing.

Authors
Li, W; Wu, B; Batrachenko, A; Bancroft-Wu, V; Morey, RA; Shashi, V; Langkammer, C; De Bellis, MD; Ropele, S; Song, AW; Liu, C
MLA Citation
Li, W, Wu, B, Batrachenko, A, Bancroft-Wu, V, Morey, RA, Shashi, V, Langkammer, C, De Bellis, MD, Ropele, S, Song, AW, and Liu, C. "Differential developmental trajectories of magnetic susceptibility in human brain gray and white matter over the lifespan." Hum Brain Mapp 35.6 (June 2014): 2698-2713.
Website
http://hdl.handle.net/10161/10981
PMID
24038837
Source
pubmed
Published In
Human Brain Mapping
Volume
35
Issue
6
Publish Date
2014
Start Page
2698
End Page
2713
DOI
10.1002/hbm.22360

Dynamic and inherent B0 correction for DTI using stimulated echo spiral imaging

Purpose To present a novel technique for high-resolution stimulated echo diffusion tensor imaging with self-navigated interleaved spirals readout trajectories that can inherently and dynamically correct for image artifacts due to spatial and temporal variations in the static magnetic field (B0) resulting from eddy currents, tissue susceptibilities, subject/physiological motion, and hardware instabilities. Methods The Hahn spin echo formed by the first two 90° radiofrequency pulses is balanced to consecutively acquire two additional images with different echo times and generate an inherent field map, while the diffusion-prepared stimulated echo signal remains unaffected. For every diffusion-encoding direction, an intrinsically registered field map is estimated dynamically and used to effectively and inherently correct for off-resonance artifacts in the reconstruction of the corresponding diffusion-weighted image. Results After correction with the dynamically acquired field maps, local blurring artifacts are specifically removed from individual stimulated echo diffusion-weighted images and the estimated diffusion tensors have significantly improved spatial accuracy and larger fractional anisotropy. Conclusion Combined with the self-navigated interleaved spirals acquisition scheme, our new method provides an integrated high-resolution short-echo time diffusion tensor imaging solution with inherent and dynamic correction for both motion-induced phase errors and off-resonance effects. © 2013 Wiley Periodicals, Inc.

Authors
Avram, AV; Guidon, A; Truong, TK; Liu, C; Song, AW
MLA Citation
Avram, AV, Guidon, A, Truong, TK, Liu, C, and Song, AW. "Dynamic and inherent B0 correction for DTI using stimulated echo spiral imaging." Magnetic Resonance in Medicine 71.3 (March 1, 2014): 1044-1053.
Source
scopus
Published In
Magnetic Resonance in Medicine
Volume
71
Issue
3
Publish Date
2014
Start Page
1044
End Page
1053
DOI
10.1002/mrm.24767

Regionally selective atrophy of subcortical structures in prodromal HD as revealed by statistical shape analysis.

Huntington disease (HD) is a neurodegenerative disorder that involves preferential atrophy in the striatal complex and related subcortical nuclei. In this article, which is based on a dataset extracted from the PREDICT-HD study, we use statistical shape analysis with deformation markers obtained through "Large Deformation Diffeomorphic Metric Mapping" of cortical surfaces to highlight specific atrophy patterns in the caudate, putamen, and globus pallidus, at different prodromal stages of the disease. On the basis of the relation to cortico-basal ganglia circuitry, we propose that statistical shape analysis, along with other structural and functional imaging studies, may help expand our understanding of the brain circuitry affected and other aspects of the neurobiology of HD, and also guide the most effective strategies for intervention.

Authors
Younes, L; Ratnanather, JT; Brown, T; Aylward, E; Nopoulos, P; Johnson, H; Magnotta, VA; Paulsen, JS; Margolis, RL; Albin, RL; Miller, MI; Ross, CA
MLA Citation
Younes, L, Ratnanather, JT, Brown, T, Aylward, E, Nopoulos, P, Johnson, H, Magnotta, VA, Paulsen, JS, Margolis, RL, Albin, RL, Miller, MI, and Ross, CA. "Regionally selective atrophy of subcortical structures in prodromal HD as revealed by statistical shape analysis." Human brain mapping 35.3 (March 2014): 792-809.
PMID
23281100
Source
epmc
Published In
Human Brain Mapping
Volume
35
Issue
3
Publish Date
2014
Start Page
792
End Page
809
DOI
10.1002/hbm.22214

Differential developmental trajectories of magnetic susceptibility in human brain gray and white matter over the lifespan

As indicated by several recent studies, magnetic susceptibility of the brain is influenced mainly by myelin in the white matter and by iron deposits in the deep nuclei. Myelination and iron deposition in the brain evolve both spatially and temporally. This evolution reflects an important characteristic of normal brain development and ageing. In this study, we assessed the changes of regional susceptibility in the human brain in vivo by examining the developmental and ageing process from 1 to 83 years of age. The evolution of magnetic susceptibility over this lifespan was found to display differential trajectories between the gray and the white matter. In both cortical and subcortical white matter, an initial decrease followed by a subsequent increase in magnetic susceptibility was observed, which could be fitted by a Poisson curve. In the gray matter, including the cortical gray matter and the iron-rich deep nuclei, magnetic susceptibility displayed a monotonic increase that can be described by an exponential growth. The rate of change varied according to functional and anatomical regions of the brain. For the brain nuclei, the age-related changes of susceptibility were in good agreement with the findings from R2* measurement. Our results suggest that magnetic susceptibility may provide valuable information regarding the spatial and temporal patterns of brain myelination and iron deposition during brain maturation and ageing. © 2013 Wiley Periodicals, Inc.

Authors
Li, W; Wu, B; Batrachenko, A; Bancroft-Wu, V; Morey, RA; Shashi, V; Langkammer, C; De Bellis, MD; Ropele, S; Song, AW; Liu, C
MLA Citation
Li, W, Wu, B, Batrachenko, A, Bancroft-Wu, V, Morey, RA, Shashi, V, Langkammer, C, De Bellis, MD, Ropele, S, Song, AW, and Liu, C. "Differential developmental trajectories of magnetic susceptibility in human brain gray and white matter over the lifespan." Human Brain Mapping 35.6 (January 1, 2014): 2698-2713.
Website
http://hdl.handle.net/10161/11644
Source
scopus
Published In
Human Brain Mapping
Volume
35
Issue
6
Publish Date
2014
Start Page
2698
End Page
2713
DOI
10.1002/hbm.22360

Cortical depth dependence of the diffusion anisotropy in the human cortical gray matter in vivo.

Diffusion tensor imaging (DTI) is typically used to study white matter fiber pathways, but may also be valuable to assess the microstructure of cortical gray matter. Although cortical diffusion anisotropy has previously been observed in vivo, its cortical depth dependence has mostly been examined in high-resolution ex vivo studies. This study thus aims to investigate the cortical depth dependence of the diffusion anisotropy in the human cortex in vivo on a clinical 3 T scanner. Specifically, a novel multishot constant-density spiral DTI technique with inherent correction of motion-induced phase errors was used to achieve a high spatial resolution (0.625 × 0.625 × 3 mm) and high spatial fidelity with no scan time penalty. The results show: (i) a diffusion anisotropy in the cortical gray matter, with a primarily radial diffusion orientation, as observed in previous ex vivo and in vivo studies, and (ii) a cortical depth dependence of the fractional anisotropy, with consistently higher values in the middle cortical lamina than in the deep and superficial cortical laminae, as observed in previous ex vivo studies. These results, which are consistent across subjects, demonstrate the feasibility of this technique for investigating the cortical depth dependence of the diffusion anisotropy in the human cortex in vivo.

Authors
Truong, T-K; Guidon, A; Song, AW
MLA Citation
Truong, T-K, Guidon, A, and Song, AW. "Cortical depth dependence of the diffusion anisotropy in the human cortical gray matter in vivo." PloS one 9.3 (January 2014): e91424-.
PMID
24608869
Source
epmc
Published In
PloS one
Volume
9
Issue
3
Publish Date
2014
Start Page
e91424
DOI
10.1371/journal.pone.0091424

A robust multi-shot scan strategy for high-resolution diffusion weighted MRI enabled by multiplexed sensitivity-encoding (MUSE).

Diffusion weighted magnetic resonance imaging (DWI) data have been mostly acquired with single-shot echo-planar imaging (EPI) to minimize motion induced artifacts. The spatial resolution, however, is inherently limited in single-shot EPI, even when the parallel imaging (usually at an acceleration factor of 2) is incorporated. Multi-shot acquisition strategies could potentially achieve higher spatial resolution and fidelity, but they are generally susceptible to motion-induced phase errors among excitations that are exacerbated by diffusion sensitizing gradients, rendering the reconstructed images unusable. It has been shown that shot-to-shot phase variations may be corrected using navigator echoes, but at the cost of imaging throughput. To address these challenges, a novel and robust multi-shot DWI technique, termed multiplexed sensitivity-encoding (MUSE), is developed here to reliably and inherently correct nonlinear shot-to-shot phase variations without the use of navigator echoes. The performance of the MUSE technique is confirmed experimentally in healthy adult volunteers on 3Tesla MRI systems. This newly developed technique should prove highly valuable for mapping brain structures and connectivities at high spatial resolution for neuroscience studies.

Authors
Chen, N-K; Guidon, A; Chang, H-C; Song, AW
MLA Citation
Chen, N-K, Guidon, A, Chang, H-C, and Song, AW. "A robust multi-shot scan strategy for high-resolution diffusion weighted MRI enabled by multiplexed sensitivity-encoding (MUSE)." Neuroimage 72 (May 15, 2013): 41-47.
PMID
23370063
Source
pubmed
Published In
NeuroImage
Volume
72
Publish Date
2013
Start Page
41
End Page
47
DOI
10.1016/j.neuroimage.2013.01.038

Integrated parallel reception, excitation, and shimming (iPRES)

Purpose: To develop a new concept for a hardware platform that enables integrated parallel reception, excitation, and shimming (iPRES). Theory: This concept uses a single coil array rather than separate arrays for parallel excitation/reception and B0 shimming. It relies on a novel design that allows a radiofrequency current (for excitation/reception) and a direct current (for B0 shimming) to coexist independently in the same coil. Methods: Proof-of-concept B0 shimming experiments were performed with a two-coil array in a phantom, whereas B0 shimming simulations were performed with a 48-coil array in the human brain. Results: Our experiments show that individually optimized direct currents applied in each coil can reduce the B0 root-mean-square error by 62-81% and minimize distortions in echo-planar images. The simulations show that dynamic shimming with the 48-coil iPRES array can reduce the B0 root-mean-square error in the prefrontal and temporal regions by 66-79% as compared with static second-order spherical harmonic shimming and by 12-23% as compared with dynamic shimming with a 48-coil conventional shim array. Conclusion: Our results demonstrate the feasibility of the iPRES concept to perform parallel excitation/reception and B0 shimming with a unified coil system as well as its promise for in vivo applications. © 2013 Wiley Periodicals, Inc.

Authors
Han, H; Song, AW; Truong, TK
MLA Citation
Han, H, Song, AW, and Truong, TK. "Integrated parallel reception, excitation, and shimming (iPRES)." Magnetic Resonance in Medicine (2013).
Source
scival
Published In
Magnetic Resonance in Medicine
Publish Date
2013
DOI
10.1002/mrm.24766

Diffuse reduction of white matter connectivity in cerebral palsy with specific vulnerability of long range fiber tracts

Cerebral palsy (CP) is a heterogeneous group of non-progressive motor disorders caused by injury to the developing fetal or infant brain. Although the defining feature of CP is motor impairment, numerous other neurodevelopmental disabilities are associated with CP and contribute greatly to its morbidity. The relationship between brain structure and neurodevelopmental outcomes in CP is complex, and current evidence suggests that motor and developmental outcomes are related to the spatial pattern and extent of brain injury. Given that multiple disabilities are frequently associated with CP, and that there is increasing burden of neurodevelopmental disability with increasing motor severity, global white matter (WM) connectivity was examined in a cohort of 17 children with bilateral CP to test the hypothesis that increased global WM damage will be seen in the group of severely affected (Gross Motor Function Classification Scale (GMFCS) level of IV) as compared to moderately affected (GMFCS of II or III) individuals. Diffusion tensor tractography was performed and the resulting fibers between anatomically defined brain regions were quantified and analyzed in relation to GMFCS levels. Overall, a reduction in total WM connectivity throughout the brain in severe versus moderate CP was observed, including but not limited to regions associated with the sensorimotor system. Our results also show a diffuse and significant reduction in global inter-regional connectivity between severity groups, represented by inter-regional fiber count, throughout the brain. Furthermore, it was also observed that there is a significant difference (p = 0.02) in long-range connectivity in patients with severe CP as compared to those with moderate CP, whereas short-range connectivity was similar between groups. This new finding, which has not been previously reported in the CP literature, demonstrates that CP may involve distributed, network-level structural disruptions. © 2013 The Authors.

Authors
Englander, ZA; Pizoli, CE; Batrachenko, A; Sun, J; Worley, G; Mikati, MA; Kurtzberg, J; Song, AW
MLA Citation
Englander, ZA, Pizoli, CE, Batrachenko, A, Sun, J, Worley, G, Mikati, MA, Kurtzberg, J, and Song, AW. "Diffuse reduction of white matter connectivity in cerebral palsy with specific vulnerability of long range fiber tracts." NeuroImage: Clinical 2.1 (2013): 440-447.
PMID
24179798
Source
scival
Published In
NeuroImage: Clinical
Volume
2
Issue
1
Publish Date
2013
Start Page
440
End Page
447
DOI
10.1016/j.nicl.2013.03.006

Dynamic and inherent B0 correction for DTI using stimulated echo spiral imaging

Purpose: To present a novel technique for high-resolution stimulated echo diffusion tensor imaging with self-navigated interleaved spirals readout trajectories that can inherently and dynamically correct for image artifacts due to spatial and temporal variations in the static magnetic field (B0) resulting from eddy currents, tissue susceptibilities, subject/physiological motion, and hardware instabilities. Methods: The Hahn spin echo formed by the first two 90° radiofrequency pulses is balanced to consecutively acquire two additional images with different echo times and generate an inherent field map, while the diffusion-prepared stimulated echo signal remains unaffected. For every diffusion-encoding direction, an intrinsically registered field map is estimated dynamically and used to effectively and inherently correct for off-resonance artifacts in the reconstruction of the corresponding diffusion-weighted image. Results: After correction with the dynamically acquired field maps, local blurring artifacts are specifically removed from individual stimulated echo diffusion-weighted images and the estimated diffusion tensors have significantly improved spatial accuracy and larger fractional anisotropy. Conclusion: Combined with the self-navigated interleaved spirals acquisition scheme, our new method provides an integrated high-resolution short-echo time diffusion tensor imaging solution with inherent and dynamic correction for both motion-induced phase errors and off-resonance effects. © 2013 Wiley Periodicals, Inc.

Authors
Avram, AV; Guidon, A; Truong, T-K; Liu, C; Song, AW
MLA Citation
Avram, AV, Guidon, A, Truong, T-K, Liu, C, and Song, AW. "Dynamic and inherent B0 correction for DTI using stimulated echo spiral imaging." Magnetic Resonance in Medicine (2013).
PMID
23630029
Source
scival
Published In
Magnetic Resonance in Medicine
Publish Date
2013
DOI
10.1002/mrm.24767

Integrated parallel reception, excitation, and shimming (iPRES)

Purpose: To develop a new concept for a hardware platform that enables integrated parallel reception, excitation, and shimming. Theory: This concept uses a single coil array rather than separate arrays for parallel excitation/reception and B0 shimming. It relies on a novel design that allows a radiofrequency current (for excitation/reception) and a direct current (for B0 shimming) to coexist independently in the same coil. Methods: Proof-of-concept B0 shimming experiments were performed with a two-coil array in a phantom, whereas B0 shimming simulations were performed with a 48-coil array in the human brain. Results: Our experiments show that individually optimized direct currents applied in each coil can reduce the B0 root-mean-square error by 62-81% and minimize distortions in echo-planar images. The simulations show that dynamic shimming with the 48-coil integrated parallel reception, excitation, and shimming array can reduce the B0 root-mean-square error in the prefrontal and temporal regions by 66-79% as compared with static second-order spherical harmonic shimming and by 12-23% as compared with dynamic shimming with a 48-coil conventional shim array. Conclusion: Our results demonstrate the feasibility of the integrated parallel reception, excitation, and shimming concept to perform parallel excitation/reception and B0 shimming with a unified coil system as well as its promise for in vivo applications. © 2012 Wiley Periodicals, Inc.

Authors
Han, H; Song, AW; Truong, T-K
MLA Citation
Han, H, Song, AW, and Truong, T-K. "Integrated parallel reception, excitation, and shimming (iPRES)." Magnetic Resonance in Medicine 70.1 (2013): 241-247.
PMID
23629974
Source
scival
Published In
Magnetic Resonance in Medicine
Volume
70
Issue
1
Publish Date
2013
Start Page
241
End Page
247
DOI
10.1002/mrm.24766

Inherent correction of motion-induced phase errors in multishot spiral diffusion-weighted imaging.

Multishot spiral imaging is a promising alternative to echo-planar imaging for high-resolution diffusion-weighted imaging and diffusion tensor imaging. However, subject motion in the presence of diffusion-weighting gradients causes phase inconsistencies among different shots, resulting in signal loss and aliasing artifacts in the reconstructed images. Such artifacts can be reduced using a variable-density spiral trajectory or a navigator echo, however at the cost of a longer scan time. Here, a novel iterative phase correction method is proposed to inherently correct for the motion-induced phase errors without requiring any additional scan time. In this initial study, numerical simulations and in vivo experiments are performed to demonstrate that the proposed method can effectively and efficiently correct for spatially linear phase errors caused by rigid-body motion in multishot spiral diffusion-weighted imaging of the human brain.

Authors
Truong, T-K; Chen, N-K; Song, AW
MLA Citation
Truong, T-K, Chen, N-K, and Song, AW. "Inherent correction of motion-induced phase errors in multishot spiral diffusion-weighted imaging." Magn Reson Med 68.4 (October 2012): 1255-1261.
PMID
22222689
Source
pubmed
Published In
Magnetic Resonance in Medicine
Volume
68
Issue
4
Publish Date
2012
Start Page
1255
End Page
1261
DOI
10.1002/mrm.24124

Functional neuroimaging of treatment effects in psychiatry: methodological challenges and recommendations.

Functional magnetic resonance imaging (fMRI) has helped to elucidate the neurobiological bases of psychiatric and neurodevelopmental disorders by localizing etiologically-relevant aberrations in brain function. Functional MRI also has shown great promise to help understand potential mechanisms of action of effective treatments for a range of psychiatric and neurodevelopmental disorders, including mood and anxiety disorders, schizophrenia, and autism. However, the use of fMRI to probe intervention effects in psychiatry is associated with unique methodological considerations, including the psychometric properties of repeated fMRI scans, how to assess potential relations between the effects of an intervention on symptoms and on specific brain activation patterns, and how to best make causal inferences about intervention effects on brain function. Additionally, the study of treatment effects in neurodevelopmental disorders presents additional unique challenges related to brain maturation, analysis methods, and the potential for motion artifacts. We review these methodological considerations and provide recommendations for best practices for each of these topics.

Authors
Dichter, GS; Sikich, L; Song, A; Voyvodic, J; Bodfish, JW
MLA Citation
Dichter, GS, Sikich, L, Song, A, Voyvodic, J, and Bodfish, JW. "Functional neuroimaging of treatment effects in psychiatry: methodological challenges and recommendations." Int J Neurosci 122.9 (September 2012): 483-493. (Review)
PMID
22471393
Source
pubmed
Published In
International Journal of Neuroscience
Volume
122
Issue
9
Publish Date
2012
Start Page
483
End Page
493
DOI
10.3109/00207454.2012.678446

Diffusion modulation of the fMRI signal: early investigations on the origin of the BOLD signal.

The early 1990s was a very special period for functional MRI (fMRI). Many original concepts were formed during that period which helped set up the foundations for modern neuroimaging development. I was fortunate to be in graduate school at the time. I was even more fortunate to be enrolled in one of the pioneer groups in fMRI at the Medical College of Wisconsin, and witnessed some of the early fMRI experiments taking place in the lab. Under the daily influence and steady guidance by the extraordinarily talented researchers there, I also began my own work on the contrast mechanisms of fMRI. In particular, I was developing diffusion weighted strategies to investigate the origin of the functional signal using blood oxygenation level dependent (BOLD) contrast. Our results, that there was significant BOLD signal in large veins and their vicinities at low field strengths (e.g. 1.5T), played an immediate role in moving fMRI applications to higher fields (3T and above) where small vessels (e.g. capillaries) contribute more significantly to improve the neuronal specificity of the BOLD signal. This manuscript gathers some of my own recollections concerning this particular development.

Authors
Song, AW
MLA Citation
Song, AW. "Diffusion modulation of the fMRI signal: early investigations on the origin of the BOLD signal." Neuroimage 62.2 (August 15, 2012): 949-952. (Review)
PMID
22245348
Source
pubmed
Published In
NeuroImage
Volume
62
Issue
2
Publish Date
2012
Start Page
949
End Page
952
DOI
10.1016/j.neuroimage.2012.01.001

The involvement of the dopaminergic midbrain and cortico-striatal-thalamic circuits in the integration of reward prospect and attentional task demands.

Reward has been shown to promote human performance in multiple task domains. However, an important debate has developed about the uniqueness of reward-related neural signatures associated with such facilitation, as similar neural patterns can be triggered by increased attentional focus independent of reward. Here, we used functional magnetic resonance imaging to directly investigate the neural commonalities and interactions between the anticipation of both reward and task difficulty, by independently manipulating these factors in a cued-attention paradigm. In preparation for the target stimulus, both factors increased activity within the midbrain, dorsal striatum, and fronto-parietal areas, while inducing deactivations in default-mode regions. Additionally, reward engaged the ventral striatum, posterior cingulate, and occipital cortex, while difficulty engaged medial and dorsolateral frontal regions. Importantly, a network comprising the midbrain, caudate nucleus, thalamus, and anterior midcingulate cortex exhibited an interaction between reward and difficulty, presumably reflecting additional resource recruitment for demanding tasks with profitable outcome. This notion was consistent with a negative correlation between cue-related midbrain activity and difficulty-induced performance detriments in reward-predictive trials. Together, the data demonstrate that expected value and attentional demands are integrated in cortico-striatal-thalamic circuits in coordination with the dopaminergic midbrain to flexibly modulate resource allocation for an effective pursuit of behavioral goals.

Authors
Krebs, RM; Boehler, CN; Roberts, KC; Song, AW; Woldorff, MG
MLA Citation
Krebs, RM, Boehler, CN, Roberts, KC, Song, AW, and Woldorff, MG. "The involvement of the dopaminergic midbrain and cortico-striatal-thalamic circuits in the integration of reward prospect and attentional task demands." Cerebral cortex (New York, N.Y. : 1991) 22.3 (March 2012): 607-615.
PMID
21680848
Source
epmc
Published In
Cerebral Cortex
Volume
22
Issue
3
Publish Date
2012
Start Page
607
End Page
615
DOI
10.1093/cercor/bhr134

Diffusion tensor imaging of cerebral white matter integrity in cognitive aging.

In this article we review recent research on diffusion tensor imaging (DTI) of white matter (WM) integrity and the implications for age-related differences in cognition. Neurobiological mechanisms defined from DTI analyses suggest that a primary dimension of age-related decline in WM is a decline in the structural integrity of myelin, particularly in brain regions that myelinate later developmentally. Research integrating behavioral measures with DTI indicates that WM integrity supports the communication among cortical networks, particularly those involving executive function, perceptual speed, and memory (i.e., fluid cognition). In the absence of significant disease, age shares a substantial portion of the variance associated with the relation between WM integrity and fluid cognition. Current data are consistent with one model in which age-related decline in WM integrity contributes to a decreased efficiency of communication among networks for fluid cognitive abilities. Neurocognitive disorders for which older adults are at risk, such as depression, further modulate the relation between WM and cognition, in ways that are not as yet entirely clear. Developments in DTI technology are providing a new insight into both the neurobiological mechanisms of aging WM and the potential contribution of DTI to understanding functional measures of brain activity. This article is part of a Special Issue entitled: Imaging Brain Aging and Neurodegenerative disease.

Authors
Madden, DJ; Bennett, IJ; Burzynska, A; Potter, GG; Chen, N-K; Song, AW
MLA Citation
Madden, DJ, Bennett, IJ, Burzynska, A, Potter, GG, Chen, N-K, and Song, AW. "Diffusion tensor imaging of cerebral white matter integrity in cognitive aging." Biochim Biophys Acta 1822.3 (March 2012): 386-400. (Review)
PMID
21871957
Source
pubmed
Published In
Biochimica et Biophysica Acta: international journal of biochemistry and biophysics
Volume
1822
Issue
3
Publish Date
2012
Start Page
386
End Page
400
DOI
10.1016/j.bbadis.2011.08.003

Acceleration of high angular and spatial resolution diffusion imaging using compressed sensing

Achieving simultaneously high angular and spatial resolution in diffusion imaging is challenging because of the long acquisition times involved. We propose a novel compressed sensing method to acquire high angular and spatial resolution diffusion imaging data, while keeping the scan time reasonable. We show that joint under sampling of 6-D k-q space is more efficient than undersampling only one of the dimensions. We use a sparse Gaussian mixture model and an iterative reconstruction scheme to recover the peaks of the orientation distribution functions (ODF) with high accuracy. We show that at least 6-fold acceleration of acquisition is possible, thereby enabling high angular and spatial resolution diffusion imaging in a reasonable scan time. © 2012 IEEE.

Authors
Mani, M; Jacob, M; Guidon, A; Liu, C; Song, A; Magnotta, V; Zhong, J
MLA Citation
Mani, M, Jacob, M, Guidon, A, Liu, C, Song, A, Magnotta, V, and Zhong, J. "Acceleration of high angular and spatial resolution diffusion imaging using compressed sensing." Proceedings - International Symposium on Biomedical Imaging (2012): 326-329.
Source
scival
Published In
Proceedings / IEEE International Symposium on Biomedical Imaging: from nano to macro. IEEE International Symposium on Biomedical Imaging
Publish Date
2012
Start Page
326
End Page
329
DOI
10.1109/ISBI.2012.6235550

Two-dimensional phase cycled reconstruction for inherent correction of echo-planar imaging Nyquist artifacts.

The inconsistency of k-space trajectories results in Nyquist artifacts in echo-planar imaging (EPI). Traditional techniques often only correct for phase errors along the frequency-encoding direction (one-dimensional correction), which may leave significant residual artifacts, particularly for oblique-plane EPI or in the presence of cross-term eddy currents. As compared with one-dimensional correction, two-dimensional (2D) phase correction can be much more effective in suppressing Nyquist artifacts. However, most existing 2D correction methods require reference scans and may not be generally applicable to different imaging protocols. Furthermore, EPI reconstruction with these 2D phase correction methods is susceptible to error amplification due to subject motion. To address these limitations, we report an inherent and general 2D phase correction technique for EPI Nyquist removal. First, a series of images are generated from the original dataset, by cycling through different possible values of phase errors using a 2D reconstruction framework. Second, the image with the lowest artifact level is identified from images generated in the first step using criteria based on background energy in sorted and sigmoid-weighted signals. In this report, we demonstrate the effectiveness of our new method in removing Nyquist ghosts in single-shot, segmented and parallel EPI without acquiring additional reference scans and the subsequent error amplifications.

Authors
Chen, N-K; Avram, AV; Song, AW
MLA Citation
Chen, N-K, Avram, AV, and Song, AW. "Two-dimensional phase cycled reconstruction for inherent correction of echo-planar imaging Nyquist artifacts." Magn Reson Med 66.4 (October 2011): 1057-1066.
PMID
21446032
Source
pubmed
Published In
Magnetic Resonance in Medicine
Volume
66
Issue
4
Publish Date
2011
Start Page
1057
End Page
1066
DOI
10.1002/mrm.22896

Dynamic correction of artifacts due to susceptibility effects and time-varying eddy currents in diffusion tensor imaging.

In diffusion tensor imaging (DTI), spatial and temporal variations of the static magnetic field (B(0)) caused by susceptibility effects and time-varying eddy currents result in severe distortions, blurring, and misregistration artifacts, which in turn lead to errors in DTI metrics and in fiber tractography. Various correction methods have been proposed, but typically assume that the eddy current-induced magnetic field can be modeled as a constant or a single exponential decay within the DTI readout window. Here, we show that its temporal dependence is more complex because of the interaction of multiple eddy currents with different time constants, but that it remains very consistent over time. As such, we propose a novel dynamic B(0) mapping and off-resonance correction method that measures the exact spatial, temporal, and diffusion-weighting direction dependence of the susceptibility- and eddy current-induced magnetic fields to effectively and efficiently correct for artifacts caused by both susceptibility effects and time-varying eddy currents, thereby resulting in a high spatial fidelity and accuracy.

Authors
Truong, T-K; Chen, N-K; Song, AW
MLA Citation
Truong, T-K, Chen, N-K, and Song, AW. "Dynamic correction of artifacts due to susceptibility effects and time-varying eddy currents in diffusion tensor imaging." Neuroimage 57.4 (August 15, 2011): 1343-1347.
PMID
21689763
Source
pubmed
Published In
NeuroImage
Volume
57
Issue
4
Publish Date
2011
Start Page
1343
End Page
1347
DOI
10.1016/j.neuroimage.2011.06.008

Structural connectivity of the frontal lobe in children with drug-resistant partial epilepsy.

The superior longitudinal fasciculus (SLF) II and cingulum are two white matter tracts important for attention and other frontal lobe functions. These functions are often disturbed in children with drug-resistant (DR) partial epilepsy, even when no abnormalities are seen on conventional MRI. We set out to determine whether abnormalities in these structures might be depicted on diffusion tensor imaging (DTI) studies in the absence of abnormalities on conventional MRI. We compared the DTI findings of 12 children with DR partial epilepsy with those of 12 age- and gender-matched controls. We found that the SLF II fractional anisotropy (FA) values of the patients were significantly lower than those of the controls (means: 0.398±0.057 and 0.443±0.059, respectively, P=0.002). Similarly, apparent diffusion coefficient (ADC) and parallel diffusivity values for SLF II were also significantly lower in the patients. There were no differences in the FA and ADC values of the cingulum. Our findings are consistent with abnormal structural connectivity of the frontal lobe in children with DR partial epilepsy and provide a possible explanation for the previously reported functional abnormalities related to the SLF II in these patients.

Authors
Holt, RL; Provenzale, JM; Veerapandiyan, A; Moon, W-J; De Bellis, MD; Leonard, S; Gallentine, WB; Grant, GA; Egger, H; Song, AW; Mikati, MA
MLA Citation
Holt, RL, Provenzale, JM, Veerapandiyan, A, Moon, W-J, De Bellis, MD, Leonard, S, Gallentine, WB, Grant, GA, Egger, H, Song, AW, and Mikati, MA. "Structural connectivity of the frontal lobe in children with drug-resistant partial epilepsy." Epilepsy Behav 21.1 (May 2011): 65-70.
PMID
21497558
Source
pubmed
Published In
Epilepsy & Behavior
Volume
21
Issue
1
Publish Date
2011
Start Page
65
End Page
70
DOI
10.1016/j.yebeh.2011.03.016

Myelin water weighted diffusion tensor imaging.

In this study we describe our development and implementation of a magnetization transfer (MT) prepared stimulated-echo diffusion tensor imaging (DTI) technique that can be made sensitive to the microanatomy of myelin tissue. The short echo time (TE) enabled by the stimulated-echo acquisition preserves significant signal from the short T(2) component (myelin water), and the MT preparation further provides differentiating sensitization to this signal. It was found that this combined strategy could provide sufficient sensitivity in our first attempt to image myelin microstructure. Compared to the diffusion tensor derived from the conventional DTI technique, the myelin water weighted (MWW) tensor has the same principal diffusion direction but exhibits a significant increase in fractional anisotropy (FA), which is mainly due to a decrease in radial diffusivity. These findings are consistent with the microstructural organization of the myelin sheaths that wrap around the axons in the white matter and therefore hinder radial diffusion. Given that many white matter diseases (e.g. multiple sclerosis) begin with a degradation of myelin microanatomy but not a loss of myelin content (e.g. loosening of the myelin sheaths), our newly implemented MWW DTI has the potential to lead to improved assessment of myelin pathology and early detection of demyelination.

Authors
Avram, AV; Guidon, A; Song, AW
MLA Citation
Avram, AV, Guidon, A, and Song, AW. "Myelin water weighted diffusion tensor imaging." Neuroimage 53.1 (October 15, 2010): 132-138.
PMID
20587369
Source
pubmed
Published In
NeuroImage
Volume
53
Issue
1
Publish Date
2010
Start Page
132
End Page
138
DOI
10.1016/j.neuroimage.2010.06.019

Application of k-space energy spectrum analysis for inherent and dynamic B0 mapping and deblurring in spiral imaging.

Spiral imaging is vulnerable to spatial and temporal variations of the amplitude of the static magnetic field (B(0)) caused by susceptibility effects, eddy currents, chemical shifts, subject motion, physiological noise, and system instabilities, resulting in image blurring. Here, a novel off-resonance correction method is proposed to address these issues. A k-space energy spectrum analysis algorithm is first applied to inherently and dynamically generate a B(0) map from the k-space data at each time point, without requiring any additional data acquisition, pulse sequence modification, or phase unwrapping. A simulated phase evolution rewinding algorithm and an automatic residual deblurring algorithm are then used to correct for the blurring caused by both spatial and temporal B(0) variations, resulting in a high spatial and temporal fidelity. This method is validated against conventional B(0) mapping and deblurring methods, and its advantages for dynamic MRI applications are demonstrated in functional MRI studies.

Authors
Truong, T-K; Chen, N-K; Song, AW
MLA Citation
Truong, T-K, Chen, N-K, and Song, AW. "Application of k-space energy spectrum analysis for inherent and dynamic B0 mapping and deblurring in spiral imaging." Magn Reson Med 64.4 (October 2010): 1121-1127.
PMID
20564589
Source
pubmed
Published In
Magnetic Resonance in Medicine
Volume
64
Issue
4
Publish Date
2010
Start Page
1121
End Page
1127
DOI
10.1002/mrm.22485

Distinct value signals in anterior and posterior ventromedial prefrontal cortex.

The core feature of an economic exchange is a decision to trade one good for another, based on a comparison of relative value. Economists have long recognized, however, that the value an individual ascribes to a good during decision making (i.e., their relative willingness to trade for that good) does not always map onto the reward they actually experience. Here, we show that experienced value and decision value are represented in distinct regions of ventromedial prefrontal cortex (VMPFC) during the passive consumption of rewards. Participants viewed two categories of rewards-images of faces that varied in their attractiveness and monetary gains and losses-while being scanned using functional magnetic resonance imaging. An independent market task, in which participants exchanged some of the money that they had earned for brief views of attractive faces, determined the relative decision value associated with each category. We found that activation of anterior VMPFC increased with increasing experienced value, but not decision value, for both reward categories. In contrast, activation of posterior VMPFC predicted each individual's relative decision value for face and monetary stimuli. These results indicate not only that experienced value and decision value are represented in distinct regions of VMPFC, but also that decision value signals are evident even in the absence of an overt choice task. We conclude that decisions are made by comparing neural representations of the value of different goods encoded in posterior VMPFC in a common, relative currency.

Authors
Smith, DV; Hayden, BY; Truong, T-K; Song, AW; Platt, ML; Huettel, SA
MLA Citation
Smith, DV, Hayden, BY, Truong, T-K, Song, AW, Platt, ML, and Huettel, SA. "Distinct value signals in anterior and posterior ventromedial prefrontal cortex." J Neurosci 30.7 (February 17, 2010): 2490-2495.
PMID
20164333
Source
pubmed
Published In
The Journal of neuroscience : the official journal of the Society for Neuroscience
Volume
30
Issue
7
Publish Date
2010
Start Page
2490
End Page
2495
DOI
10.1523/JNEUROSCI.3319-09.2010

The Saccadic Re-Centering Bias is Associated with Activity Changes in the Human Superior Colliculus.

Being able to effectively explore our visual world is of fundamental importance, and it has been suggested that the straight-ahead gaze (primary position) might play a special role in this context. We employed fMRI in humans to investigate how neural activity might be modulated for saccades relative to this putative default position. Using an endogenous cueing paradigm, saccade direction and orbital starting position were systematically manipulated, resulting in saccades toward primary position (centripetal) and away from primary position (centrifugal) that were matched in amplitude, directional predictability, as well as orbital starting position. In accord with earlier research, we found that fMRI activity in the superior colliculus (SC), as well as in the frontal eye fields and the intraparietal sulcus, was enhanced contralateral to saccade direction across all saccade conditions. Furthermore, the SC exhibited a relative activity decrease during re-centering relative to centrifugal saccades, a pattern that was paralleled by faster saccadic reaction times. In contrast, activity within the cortical eye fields was not significantly modulated during re-centering saccades as compared to other saccade types, suggesting that the re-centering bias is predominantly implemented at a subcortical rather than cortical processing stage. Such a modulation might reflect a special coding bias facilitating the return of gaze to a default position in the gaze space in which retinotopic and egocentric reference frames are aligned and from which the visual world can be effectively explored.

Authors
Krebs, RM; Schoenfeld, MA; Boehler, CN; Song, AW; Woldorff, MG
MLA Citation
Krebs, RM, Schoenfeld, MA, Boehler, CN, Song, AW, and Woldorff, MG. "The Saccadic Re-Centering Bias is Associated with Activity Changes in the Human Superior Colliculus. (Published online)" Front Hum Neurosci 4 (2010): 193-.
PMID
21103010
Source
pubmed
Published In
Frontiers in Human Neuroscience
Volume
4
Publish Date
2010
Start Page
193
DOI
10.3389/fnhum.2010.00193

White matter abnormalities in bipolar disorder: Insights from diffusion tensor imaging studies

Diffusion tensor imaging (DTI) is a neuroimaging technique with the potential to elucidate white matter abnormalities. Recently, it has been applied to help in better understanding of the pathophysiology of bipolar disorder (BD). This review sought to synthesise existing literature on DTI studies in BD, summarise current findings and highlight brain regions that have consistently been implicated in BD, as well as posit possible future directions for DTI research in BD. The extant findings from this review suggest loss of white matter network connectivity as a possible phenomenon associated with bipolar disorder, involving prefrontal and frontal regions, projection, associative and commissural fibres, with sparse and less consistent evidence implicating the subcortical and non-frontal lobes of the brain. There are some differences in the direction of changes observed in white matter indices, and these may be attributed to factors including sample heterogeneity and limitations of DTI techniques. The possible roles of the parietal, temporal and occipital lobes and subcortical regions in BD await further investigation. Studies of bipolar disorder using DTI lag behind other neuropsychiatric diseases such as schizophrenia, but DTI research in BD is fast gaining pace. The emerging trends from these DTI findings underscore the importance of further research to unravel the underlying neural mechanisms and clinico-anatomical correlations involving white matter in BD. © 2010 Springer-Verlag.

Authors
Heng, S; Song, AW; Sim, K
MLA Citation
Heng, S, Song, AW, and Sim, K. "White matter abnormalities in bipolar disorder: Insights from diffusion tensor imaging studies." Journal of Neural Transmission 117.5 (2010): 639-654.
PMID
20107844
Source
scival
Published In
Journal of Neural Transmission
Volume
117
Issue
5
Publish Date
2010
Start Page
639
End Page
654
DOI
10.1007/s00702-010-0368-9

Apparent diffusion coefficient dependent fMRI: Spatiotemporal characteristics and implications on calibrated fMRI

In this manuscript, we review the development of an alternative functional magnetic resonance imaging (fMRI) contrast mechanism based on the apparent diffusion coefficient (ADC), in light of the recent progress in other complementary functional imaging contrasts sensitive to cerebral blood flow (CBF) and cerebral blood volume (CBV). Specifically, we discuss the spatial and temporal characteristics of ADC fMRI in localizing neuronal activities, and also draw inference on its potential applicability to achieve fast calibrated fMRI. We found that optimized dynamic ADC contrast can lead to improved spatial localization in small vessel networks close to the true neuronal activities, while having the potential to simultaneously generate the blood oxygenation level-dependent (BOLD) and CBF/CBV contrasts required in a calibrated fMRI experiment. With sufficient signal-to-noise ratio (SNR) and temporal resolution, fMRI based on the dynamic ADC contrast may prove to be an efficient technique to achieve accurate and quantitative measures of neuronal activities. © 2010 Wiley Periodicals, Inc.

Authors
Song, AW; Truong, T-K
MLA Citation
Song, AW, and Truong, T-K. "Apparent diffusion coefficient dependent fMRI: Spatiotemporal characteristics and implications on calibrated fMRI." International Journal of Imaging Systems and Technology 20.1 (2010): 42-50.
Source
scival
Published In
International Journal of Imaging Systems and Technology
Volume
20
Issue
1
Publish Date
2010
Start Page
42
End Page
50
DOI
10.1002/ima.20220

Cerebral white matter integrity and cognitive aging: contributions from diffusion tensor imaging.

The integrity of cerebral white matter is critical for efficient cognitive functioning, but little is known regarding the role of white matter integrity in age-related differences in cognition. Diffusion tensor imaging (DTI) measures the directional displacement of molecular water and as a result can characterize the properties of white matter that combine to restrict diffusivity in a spatially coherent manner. This review considers DTI studies of aging and their implications for understanding adult age differences in cognitive performance. Decline in white matter integrity contributes to a disconnection among distributed neural systems, with a consistent effect on perceptual speed and executive functioning. The relation between white matter integrity and cognition varies across brain regions, with some evidence suggesting that age-related effects exhibit an anterior-posterior gradient. With continued improvements in spatial resolution and integration with functional brain imaging, DTI holds considerable promise, both for theories of cognitive aging and for translational application.

Authors
Madden, DJ; Bennett, IJ; Song, AW
MLA Citation
Madden, DJ, Bennett, IJ, and Song, AW. "Cerebral white matter integrity and cognitive aging: contributions from diffusion tensor imaging." Neuropsychol Rev 19.4 (December 2009): 415-435. (Review)
PMID
19705281
Source
pubmed
Published In
Neuropsychology Review
Volume
19
Issue
4
Publish Date
2009
Start Page
415
End Page
435
DOI
10.1007/s11065-009-9113-2

Measurement of spontaneous signal fluctuations in fMRI: adult age differences in intrinsic functional connectivity.

Functional connectivity (FC) reflects the coherence of spontaneous, low-frequency fluctuations in functional magnetic resonance imaging (fMRI) data. We report a behavior-based connectivity analysis method, in which whole-brain data are used to identify behaviorally relevant, intrinsic FC networks. Nineteen younger adults (20-28 years) and 19 healthy, older adults (63-78 years) were assessed with fMRI and diffusion tensor imaging (DTI). Results indicated that FC involving a distributed network of brain regions, particularly the inferior frontal gyri, exhibited age-related change in the correlation with perceptual-motor speed (choice reaction time; RT). No relation between FC and RT was evident for younger adults, whereas older adults exhibited a significant age-related slowing of perceptual-motor speed, which was mediated by decreasing FC. Older adults' FC values were in turn associated positively with white matter integrity (from DTI) within the genu of the corpus callosum. The developed FC analysis illustrates the value of identifying connectivity by combining structural, functional, and behavioral data.

Authors
Chen, N-K; Chou, Y-H; Song, AW; Madden, DJ
MLA Citation
Chen, N-K, Chou, Y-H, Song, AW, and Madden, DJ. "Measurement of spontaneous signal fluctuations in fMRI: adult age differences in intrinsic functional connectivity." Brain structure & function 213.6 (October 2009): 571-585.
PMID
19727810
Source
epmc
Published In
Brain Structure and Function
Volume
213
Issue
6
Publish Date
2009
Start Page
571
End Page
585
DOI
10.1007/s00429-009-0218-4

Cortical depth dependence and implications on the neuronal specificity of the functional apparent diffusion coefficient contrast.

Although the blood oxygenation level-dependent (BOLD) contrast is widely used in functional MRI (fMRI), its spatial specificity is compromised by the diversity of the participating vasculature, including large draining veins. Previous studies have shown that an alternative contrast mechanism based on functional changes of the apparent diffusion coefficient (ADC) can be sensitized to small vessels more closely tied to the sites of neural activity. Such an improved functional localization, however, has not yet been demonstrated at the cortical level in humans. Here, we investigate the cortical depth dependence and neuronal specificity of the functional ADC contrast in the human primary visual cortex by performing high-resolution BOLD and ADC imaging during visual stimulation at 4 T. Our results show that, by using optimal parameters, the functional ADC changes are significantly higher in the middle cortical layers, whereas the BOLD signal changes are higher at the cortical surface and vary much less significantly across the cortex. These results are in good agreement with previous studies performed in anesthetized cats at 9.4 T and demonstrate the improved spatial specificity of the functional ADC contrast as compared to the BOLD contrast.

Authors
Truong, T-K; Song, AW
MLA Citation
Truong, T-K, and Song, AW. "Cortical depth dependence and implications on the neuronal specificity of the functional apparent diffusion coefficient contrast." Neuroimage 47.1 (August 1, 2009): 65-68.
PMID
19379817
Source
pubmed
Published In
NeuroImage
Volume
47
Issue
1
Publish Date
2009
Start Page
65
End Page
68
DOI
10.1016/j.neuroimage.2009.04.045

Biochemical abnormalities of the medial temporal lobe and medial prefrontal cortex in late-life depression.

We utilized single-voxel (1)H magnetic resonance spectroscopy (MRS) to investigate biochemical abnormalities related to late-life depression in the medial prefrontal cortex and medial temporal lobe. Fourteen elderly subjects whose depression responded to treatment and 12 nondepressed subjects were enrolled. Subjects were scanned using a GE 3.0 Tesla whole body MR scanner. Metabolite concentrations were quantified using the LC Model software and adjusted for CSF and ratio of gray to white matter. ANCOVA models tested for group differences while controlling for age and sex. Older previously depressed individuals showed significantly reduced concentrations of total N-acetyl aspartate (NAA), choline, and creatine in the prefrontal cortex and significantly elevated left medial temporal lobe concentrations of NAA and myo-inositol. There were no significant group differences in right temporal metabolite concentrations. The prefrontal cortex observations suggest that reduced neuronal, phospolipid, and energy metabolism is present even in clinically improved depression. In contrast, elevated NAA and myo-inositol concentrations in the left medial temporal lobe could be associated with neuronal and glial cell changes in the amygdala.

Authors
Venkatraman, TN; Krishnan, RR; Steffens, DC; Song, AW; Taylor, WD
MLA Citation
Venkatraman, TN, Krishnan, RR, Steffens, DC, Song, AW, and Taylor, WD. "Biochemical abnormalities of the medial temporal lobe and medial prefrontal cortex in late-life depression." Psychiatry Res 172.1 (April 30, 2009): 49-54.
PMID
19179054
Source
pubmed
Published In
Psychiatry Research
Volume
172
Issue
1
Publish Date
2009
Start Page
49
End Page
54
DOI
10.1016/j.pscychresns.2008.07.001

Dynamic MRI of small electrical activity

Neuroscience methods entailing in vivo measurements of brain activity have greatly contributed to our understanding of brain function for the past decades, from the invasive early studies in animals using single-cell electrical recordings, to the noninvasive techniques in humans of scalp-recorded electroencephalography (EEG) and magnetoencephalography (MEG), positron emission tomography (PET), and, most recently, blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI). A central objective of these techniques is to measure neuronal activities with high spatial and temporal resolution. Each of these methods, however, has substantial limitations in this regard. Single-cell recording is invasive and only typically records cellular activity in a single location; EEG/MEG cannot generally provide accurate and unambiguous delineations of neuronal activation spatially; and the most sophisticated BOLD-based fMRI methods are still fundamentally limited by their dependence on the very slow hemodynamic responses upon which they are based. Even the latest neuroimaging methodology (e.g., multimodal EEG/fMRI) does not yet unambiguously provide accurate localization of neuronal activation spatially and temporally. There is hence a need to further develop noninvasive imaging methods that can directly image neuroelectric activity and thus truly achieve a high temporal resolution and spatial specificity in humans. Here, we discuss the theory, implementation, and potential utility of an MRI technique termed Lorentz effect imaging (LEI) that can detect spatially incoherent yet temporally synchronized, minute electrical activities in the neural amplitude range (microamperes) when they occur in a strong magnetic field. Moreover, we demonstrate with our preliminary results in phantoms and in vivo, the feasibility of imaging such activities with a temporal resolution on the order of milliseconds. © 2009 Humana Press.

Authors
Song, AW; Truong, T-K; Woldorff, M
MLA Citation
Song, AW, Truong, T-K, and Woldorff, M. "Dynamic MRI of small electrical activity." Methods in Molecular Biology 489 (2009): 297-315.
Source
scival
Published In
Methods in molecular biology (Clifton, N.J.)
Volume
489
Publish Date
2009
Start Page
297
End Page
315
DOI
10.1007/978-1-59745-543-5_14

Dynamic MRI of small electrical activity.

Neuroscience methods entailing in vivo measurements of brain activity have greatly contributed to our understanding of brain function for the past decades, from the invasive early studies in animals using single-cell electrical recordings, to the noninvasive techniques in humans of scalp-recorded electroencephalography (EEG) and magnetoencephalography (MEG), positron emission tomography (PET), and, most recently, blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI). A central objective of these techniques is to measure neuronal activities with high spatial and temporal resolution. Each of these methods, however, has substantial limitations in this regard. Single-cell recording is invasive and only typically records cellular activity in a single location; EEG/MEG cannot generally provide accurate and unambiguous delineations of neuronal activation spatially; and the most sophisticated BOLD-based fMRI methods are still fundamentally limited by their dependence on the very slow hemodynamic responses upon which they are based. Even the latest neuroimaging methodology (e.g., multimodal EEG/fMRI) does not yet unambiguously provide accurate localization of neuronal activation spatially and temporally. There is hence a need to further develop noninvasive imaging methods that can directly image neuroelectric activity and thus truly achieve a high temporal resolution and spatial specificity in humans. Here, we discuss the theory, implementation, and potential utility of an MRI technique termed Lorentz effect imaging (LEI) that can detect spatially incoherent yet temporally synchronized, minute electrical activities in the neural amplitude range (microamperes) when they occur in a strong magnetic field. Moreover, we demonstrate with our preliminary results in phantoms and in vivo, the feasibility of imaging such activities with a temporal resolution on the order of milliseconds.

Authors
Song, AW; Truong, T-K; Woldorff, M
MLA Citation
Song, AW, Truong, T-K, and Woldorff, M. "Dynamic MRI of small electrical activity." Methods Mol Biol 489 (2009): 297-315.
PMID
18839098
Source
pubmed
Published In
Methods in molecular biology (Clifton, N.J.)
Volume
489
Publish Date
2009
Start Page
297
End Page
315
DOI
10.1007/978-1-59745-543-5_14

Measurement of spontaneous signal fluctuations in fMRI: adult age differences in intrinsic functional connectivity

Functional connectivity (FC) reflects the coherence of spontaneous, low-frequency fluctuations in functional magnetic resonance imaging (fMRI) data. We report a behavior-based connectivity analysis method, in which whole-brain data are used to identify behaviorally relevant, intrinsic FC networks. Nineteen younger adults (20-28 years) and 19 healthy, older adults (63-78 years) were assessed with fMRI and diffusion tensor imaging (DTI). Results indicated that FC involving a distributed network of brain regions, particularly the inferior frontal gyri, exhibited age-related change in the correlation with perceptual-motor speed (choice reaction time; RT). No relation between FC and RT was evident for younger adults, whereas older adults exhibited a significant age-related slowing of perceptual-motor speed, which was mediated by decreasing FC. Older adults' FC values were in turn associated positively with white matter integrity (from DTI) within the genu of the corpus callosum. The developed FC analysis illustrates the value of identifying connectivity by combining structural, functional, and behavioral data. © 2009 Springer-Verlag.

Authors
Chen, NK; Chou, YH; Song, AW; Madden, DJ
MLA Citation
Chen, NK, Chou, YH, Song, AW, and Madden, DJ. "Measurement of spontaneous signal fluctuations in fMRI: adult age differences in intrinsic functional connectivity." Brain Structure and Function (2009): 1-15.
Source
scival
Published In
Brain Structure and Function
Publish Date
2009
Start Page
1
End Page
15
DOI
10.1007/s00429-009-0218-4

Investigations on spinal cord fMRI of cats under ketamine

Functional magnetic resonance imaging (fMRI) of the spinal cord has been the subject of intense research for the last ten years. An important motivation for this technique is its ability to detect non-invasively neuronal activity in the spinal cord related to sensorimotor functions in various conditions, such as after spinal cord lesions. Although promising results of spinal cord fMRI have arisen from previous studies, the poor reproducibility of BOLD activations and their characteristics remain a major drawback. In the present study we investigated the reproducibility of BOLD fMRI in the spinal cord of cats (N = 9) by repeating the same stimulation protocol over a long period (∼ 2 h). Cats were anaesthetized with ketamine, and spinal cord activity was induced by electrical stimulation of cutaneous nerves of the hind limbs. As a result, task-related signals were detected in most cats with relatively good spatial specificity. However, BOLD response significantly varied within and between cats. This variability was notably attributed to the moderate intensity of the stimulus producing a low amplitude haemodynamic response, variation in end-tidal CO2 during the session, low signal-to-noise ratio (SNR) in spinal fMRI time series and animal-specific vascular anatomy. Original contributions of the present study are: (i) first spinal fMRI experiment in ketamine-anaesthetized animals, (ii) extensive study of intra- and inter-subject variability of activation, (iii) characterisation of static and temporal SNR in the spinal cord and (iv) investigation on the impact of CO2 end-tidal level on the amplitude of BOLD response. © 2008.

Authors
Cohen-Adad, J; Hoge, RD; Leblond, H; Xie, G; Beaudoin, G; Song, AW; Krueger, G; Doyon, J; Benali, H; Rossignol, S
MLA Citation
Cohen-Adad, J, Hoge, RD, Leblond, H, Xie, G, Beaudoin, G, Song, AW, Krueger, G, Doyon, J, Benali, H, and Rossignol, S. "Investigations on spinal cord fMRI of cats under ketamine." NeuroImage 44.2 (2009): 328-339.
PMID
18938251
Source
scival
Published In
NeuroImage
Volume
44
Issue
2
Publish Date
2009
Start Page
328
End Page
339
DOI
10.1016/j.neuroimage.2008.09.023

Differentiating sensitivity of post-stimulus undershoot under diffusion weighting: implication of vascular and neuronal hierarchy.

The widely used blood oxygenation level dependent (BOLD) signal during brain activation, as measured in typical fMRI methods, is composed of several distinct phases, the last of which, and perhaps the least understood, is the post-stimulus undershoot. Although this undershoot has been consistently observed, its hemodynamic and metabolic sources are still under debate, as evidences for sustained blood volume increases and metabolic activities have been presented. In order to help differentiate the origins of the undershoot from vascular and neuronal perspectives, we applied progressing diffusion weighting gradients to investigate the BOLD signals during visual stimulation. Three distinct regions were established and found to have fundamentally different properties in post-stimulus signal undershoot. The first region, with a small but focal spatial extent, shows a clear undershoot with decreasing magnitude under increasing diffusion weighting, which is inferred to represent intravascular signal from larger vessels with large apparent diffusion coefficients (ADC), or high mobility. The second region, with a large continuous spatial extent in which some surrounds the first region while some spreads beyond, also shows a clear undershoot but no change in undershoot amplitude with progressing diffusion weighting. This would indicate a source based on extravascular and small vessel signal with smaller ADC, or lower mobility. The third region shows no significant undershoot, and is largely confined to higher order visual areas. Given their intermediate ADC, it would likely include both large and small vessels. Thus the consistent observation of this third region would argue against a vascular origin but support a metabolic basis for the post-stimulus undershoot, and would appear to indicate a lack of sustained metabolic rate likely due to a lower oxygen metabolism in these higher visual areas. Our results are the first, to our knowledge, to suggest that the post-stimulus undershoots have a spatial dependence on the vascular and neuronal hierarchy, and that progressing flow-sensitized diffusion weighting can help delineate these dependences.

Authors
Harshbarger, TB; Song, AW
MLA Citation
Harshbarger, TB, and Song, AW. "Differentiating sensitivity of post-stimulus undershoot under diffusion weighting: implication of vascular and neuronal hierarchy. (Published online)" PLoS One 3.8 (August 13, 2008): e2914-.
Website
http://hdl.handle.net/10161/13718
PMID
18698432
Source
pubmed
Published In
PloS one
Volume
3
Issue
8
Publish Date
2008
Start Page
e2914
DOI
10.1371/journal.pone.0002914

Integrated SENSE DTI with correction of susceptibility- and eddy current-induced geometric distortions.

Diffusion tensor imaging (DTI) is vulnerable to geometric distortions caused by subject-dependent susceptibility effects and diffusion-weighting direction-dependent eddy currents. Although the introduction of sensitivity encoding (SENSE) has reduced the overall distortions for the same imaging matrix size, this benefit is offset by the increasing demand for higher spatial resolution. Thus, significant distortions remain or are exacerbated in high-resolution SENSE DTI acquisitions. While the susceptibility-induced distortions cause global spatial misregistration, the direction-dependent eddy current-induced distortions cause misregistration among different diffusion-weighted images, leading to errors in the derivation of the diffusion tensor in virtually all voxels, and consequently in resulting diffusion parameters as well as in fiber tracking. Here, we apply a comprehensive approach that corrects for both susceptibility- and eddy current-induced distortions to high-resolution SENSE DTI acquisitions, and demonstrate its effectiveness, efficiency, and reliability in vivo as well as its advantages over a twice-refocused spin-echo sequence. This method should find increased use in modern DTI experiments where SENSE acquisitions are commonly used.

Authors
Truong, T-K; Chen, B; Song, AW
MLA Citation
Truong, T-K, Chen, B, and Song, AW. "Integrated SENSE DTI with correction of susceptibility- and eddy current-induced geometric distortions." Neuroimage 40.1 (March 1, 2008): 53-58.
PMID
18187344
Source
pubmed
Published In
NeuroImage
Volume
40
Issue
1
Publish Date
2008
Start Page
53
End Page
58
DOI
10.1016/j.neuroimage.2007.12.001

Lorentz effect imaging of ionic currents in solution.

Current functional MRI techniques relying on hemodynamic modulations are inherently limited in their ability to accurately localize neural activity in space and time. To address these limitations, we previously proposed a novel technique based on the Lorentz effect and demonstrated its ability to directly image minute electrical activity with a millisecond temporal resolution in gel phantoms containing conductive wires as well as in the human median nerve in vivo. To better characterize its contrast mechanism and ultimately further improve its sensitivity for in vivo applications, we now apply this technique to image ionic currents in solution, which serve as a better model for neural conduction in biological systems than the electronic currents in conductive wires used in previous phantom studies. Our results demonstrate that ionic currents with durations and current densities on the same order of magnitude as those induced by neuroelectric activity in nerve fibers and in the brain can be detected.

Authors
Truong, T-K; Avram, A; Song, AW
MLA Citation
Truong, T-K, Avram, A, and Song, AW. "Lorentz effect imaging of ionic currents in solution." J Magn Reson 191.1 (March 2008): 93-99.
PMID
18180187
Source
pubmed
Published In
Journal of Magnetic Resonance
Volume
191
Issue
1
Publish Date
2008
Start Page
93
End Page
99
DOI
10.1016/j.jmr.2007.12.005

Single-shot dual-z-shimmed sensitivity-encoded spiral-in/out imaging for functional MRI with reduced susceptibility artifacts.

Blood oxygenation level-dependent (BOLD) functional MRI (fMRI) can be severely hampered by signal loss due to susceptibility-induced static magnetic field (B(0)) inhomogeneities near air/tissue interfaces. A single-shot spiral-in/out sequence with a z-shim gradient embedded between the two acquisitions was previously proposed to efficiently recover the signal. However, despite promising results, this technique had several limitations, which are addressed here as follows. First, by adding a second z-shim gradient before the spiral-in acquisition and optimizing both z-shim gradients slice-by-slice, a significantly more uniform signal recovery can be achieved. Second, by acquiring a B(0) map, the optimal z-shim gradients can be directly, efficiently, and accurately determined for each subject. Third, by complementing the z-shimming approach with sensitivity encoding (SENSE), the in-plane spatial resolution can be increased and, hence, susceptibility artifacts further reduced, while maintaining a high temporal resolution for fMRI applications. These advantages are demonstrated in human functional studies.

Authors
Truong, T-K; Song, AW
MLA Citation
Truong, T-K, and Song, AW. "Single-shot dual-z-shimmed sensitivity-encoded spiral-in/out imaging for functional MRI with reduced susceptibility artifacts." Magn Reson Med 59.1 (January 2008): 221-227.
PMID
18050341
Source
pubmed
Published In
Magnetic Resonance in Medicine
Volume
59
Issue
1
Publish Date
2008
Start Page
221
End Page
227
DOI
10.1002/mrm.21473

Diffusion tensor imaging fiber tracking with local tissue property sensitivity: phantom and in vivo validation.

Diffusion tensor imaging (DTI) provides directional information that can be used to delineate brain white matter connections noninvasively via fiber tracking. The most commonly used methods for tractography are based on the streamline tracking algorithm for track propagation and a set of empirically and globally defined criteria for track termination. In this study, we propose a streamline tracking algorithm with high-order propagation accuracy and a single termination criterion based on tissue property to minimize user intervention and biases introduced during tracking process. These advantages and the agreement with histological reports are demonstrated in our tracking results in phantoms and in humans.

Authors
Chen, B; Song, AW
MLA Citation
Chen, B, and Song, AW. "Diffusion tensor imaging fiber tracking with local tissue property sensitivity: phantom and in vivo validation." Magn Reson Imaging 26.1 (January 2008): 103-108.
PMID
17587528
Source
pubmed
Published In
Magnetic Resonance Imaging
Volume
26
Issue
1
Publish Date
2008
Start Page
103
End Page
108
DOI
10.1016/j.mri.2007.05.003

Component structure of event-related fMRI responses in the different neurovascular compartments.

In most functional magnetic resonance imaging (fMRI) studies, brain activity is localized by observing changes in the blood oxygenation level-dependent (BOLD) signal that are believed to arise from capillaries, venules and veins in and around the active neuronal population. However, the contribution from veins can be relatively far downstream from active neurons, thereby limiting the ability of BOLD imaging methods to precisely pinpoint neural generators. Hemodynamic measures based on apparent diffusion coefficients (ADCs) have recently been used to identify more upstream functional blood flow changes in the capillaries, arterioles and arteries. In particular, we recently showed that, due to the complementary vascular sensitivities of ADC and BOLD signals, the voxels conjointly activated by both measures may identify the capillary networks of the active neuronal areas. In this study, we first used simultaneously acquired ADC and BOLD functional imaging signals to identify brain voxels activated by ADC only, by both ADC and BOLD and by BOLD only, thereby delineating voxels relatively dominated by the arterial, capillary, and draining venous neurovascular compartments, respectively. We then examined the event-related fMRI BOLD responses in each of these delineated neurovascular compartments, hypothesizing that their event-related responses would show different temporal componentries. In the regions activated by both the BOLD and ADC contrasts, but not in the BOLD-only areas, we observed an initial transient signal reduction (an initial dip), consistent with the local production of deoxyhemoglobin by the active neuronal population. In addition, the BOLD-ADC overlap areas and the BOLD-only areas showed a clear poststimulus undershoot, whereas the compartment activated by only ADC did not show this component. These results indicate that using ADC contrast in conjunction with BOLD imaging can help delineate the various neurovascular compartments, improve the localization of active neural populations, and provide insight into the physiological mechanisms underlying the hemodynamic signals.

Authors
Roberts, KC; Tran, TT; Song, AW; Woldorff, MG
MLA Citation
Roberts, KC, Tran, TT, Song, AW, and Woldorff, MG. "Component structure of event-related fMRI responses in the different neurovascular compartments." Magnetic resonance imaging 25.3 (April 2007): 328-334.
PMID
17371721
Source
epmc
Published In
Magnetic Resonance Imaging
Volume
25
Issue
3
Publish Date
2007
Start Page
328
End Page
334
DOI
10.1016/j.mri.2006.08.010

Single-shot ADC imaging for fMRI.

It has been suggested that apparent diffusion coefficient (ADC) contrast can be sensitive to cerebral blood flow (CBF) changes during brain activation. However, current ADC imaging techniques have an inherently low temporal resolution due to the requirement of multiple acquisitions with different b-factors, as well as potential confounds from cross talk between the deoxyhemoglobin-induced background gradients and the externally applied diffusion-weighting gradients. In this report a new method is proposed and implemented that addresses these two limitations. Specifically, a single-shot pulse sequence that sequentially acquires one gradient-echo (GRE) and two diffusion-weighted spin-echo (SE) images was developed. In addition, the diffusion-weighting gradient waveform was numerically optimized to null the cross terms with the deoxyhemoglobin-induced background gradients to fully isolate the effect of diffusion weighting from that of oxygenation-level changes. The experimental results show that this new single-shot method can acquire ADC maps with sufficient signal-to-noise ratio (SNR), and establish its practical utility in functional MRI (fMRI) to complement the blood oxygenation level-dependent (BOLD) technique and provide differential sensitivity for different vasculatures to better localize neural activity originating from the small vessels.

Authors
Song, AW; Guo, H; Truong, T-K
MLA Citation
Song, AW, Guo, H, and Truong, T-K. "Single-shot ADC imaging for fMRI." Magn Reson Med 57.2 (February 2007): 417-422.
PMID
17260372
Source
pubmed
Published In
Magnetic Resonance in Medicine
Volume
57
Issue
2
Publish Date
2007
Start Page
417
End Page
422
DOI
10.1002/mrm.21135

Endogenous functional CBV contrast revealed by diffusion weighting.

Functional MRI (fMRI) based on the blood oxygenation level dependent (BOLD) contrast often suffers from a lack of specificity because of the vascular spread of oxygenation changes. It is suggested from the optical imaging and animal fMRI literature that cerebral blood volume (CBV) changes are more closely tied to the smaller vessels. As such, fMRI contrast based on CBV changes will have improved spatial specificity to the neuronal activities as they are immediately adjacent to the smaller vessels. In this paper, an endogenous contrast mechanism based on a diffusion weighting strategy that could detect functional CBV changes is presented. Initially, a theoretical framework is presented to model the functional signal changes as a function of CBV under diffusion weighting, which predicts peak CBV sensitivity at various vessel-tissue mixtures. It was found that a b factor over 1500 s/mm(2) would be necessary to achieve dominant CBV contrast. Further, two sets of experimental results are also presented. In the first experiment, diffusion weighting at a set of b factors ranging from 300 to 600 s/mm(2) was used. The results indicated that while the positive activation (predominantly BOLD signal) continued to reduce in magnitude and spatial extent, the negative activation (predominantly CBV signal) remained virtually constant with increasing b factors. The second experiment used a b factor of 1600 s/mm(2) and showed extensive negative activation in the visual cortex and greatly reduced positive activations compared with images with no diffusion weighting. The time course of negative activation showed a faster time to peak and return to baseline than the positive BOLD activity, consistent with the small vessel origin of the signal changes. These results suggest that appropriate diffusion weighting could be used to measure activation related CBV changes.

Authors
Harshbarger, TB; Song, AW
MLA Citation
Harshbarger, TB, and Song, AW. "Endogenous functional CBV contrast revealed by diffusion weighting." NMR Biomed 19.8 (December 2006): 1020-1027.
PMID
16894639
Source
pubmed
Published In
Nmr in Biomedicine
Volume
19
Issue
8
Publish Date
2006
Start Page
1020
End Page
1027
DOI
10.1002/nbm.1067

Finding neuroelectric activity under magnetic-field oscillations (NAMO) with magnetic resonance imaging in vivo.

Neuroimaging techniques are among the most important tools for investigating the function of the human nervous system and for improving the clinical diagnosis of neurological disorders. However, most commonly used techniques are limited by their invasiveness or their inability to accurately localize neural activity in space or time. Previous attempts at using MRI to directly image neuroelectric activity in vivo through the detection of magnetic field changes induced by neuronal currents have been challenging because of the extremely small signal changes and confounding factors such as hemodynamic modulations. Here we describe an MRI technique that uses oscillating magnetic field gradients to significantly amplify and detect the Lorentz effect induced by neuroelectric activity, and we demonstrate its effectiveness in imaging sensory nerve activation in vivo in the human median nerve during electrical stimulation of the wrist. This direct, real-time, and noninvasive neuroimaging technique may potentially find broad applications in neurosciences.

Authors
Truong, T-K; Song, AW
MLA Citation
Truong, T-K, and Song, AW. "Finding neuroelectric activity under magnetic-field oscillations (NAMO) with magnetic resonance imaging in vivo." Proc Natl Acad Sci U S A 103.33 (August 15, 2006): 12598-12601.
PMID
16894177
Source
pubmed
Published In
Proceedings of the National Academy of Sciences of USA
Volume
103
Issue
33
Publish Date
2006
Start Page
12598
End Page
12601
DOI
10.1073/pnas.0605486103

Dependence of gradient-echo and spin-echo BOLD fMRI at 4 T on diffusion weighting.

Diffusion weighting and spin-echo (SE) acquisitions can be used to help improve the spatial localization of BOLD fMRI at the cost of reduced acquisition rates and lower signal-to-noise ratio (SNR). To evaluate these costs, SE and gradient-echo (GE) data were acquired at 4 T at five diffusion weightings ranging from b = 0 to 1110 s/mm(2) using a robust visual stimulus. The data showed reduced functional contrast when diffusion weighting was applied. As the amount of diffusion weighting increased, the functional contrast initially dropped sharply, and then remained relatively constant for diffusion weightings above 15 s/mm(2) for SE and 30 s/mm(2) for GE data. GE functional BOLD contrast was attenuated to 94.0 +/- 10.1, 87.6 +/- 12.2, 86.4 +/- 8.8 and 83.3 +/- 20.6% of the non-diffusion-weighted GE contrast for diffusion weightings of 15, 30, 200 and 1,110 s/mm(2). The non-diffusion-weighted SE contrast greatly reduced to 19.3 +/- 3.3% of the non-diffusion-weighted GE contrast, demonstrating the large activation attenuation of a SE acquisition. The SE contrast was further reduced to 10.0 +/- 3.6, 9.0 +/- 2.5 and 8.6 +/- 2.0% of the non-diffusion-weighted GE contrast for the 15, 30 and 200 s/mm(2) diffusion-weighted data. These results suggest that only a small amount of diffusion weighting is necessary to suppress the vascular contribution and spin-echo imaging should only be used if there is adequate statistical power available or accurate localization is critical.

Authors
Michelich, CR; Song, AW; Macfall, JR
MLA Citation
Michelich, CR, Song, AW, and Macfall, JR. "Dependence of gradient-echo and spin-echo BOLD fMRI at 4 T on diffusion weighting." NMR Biomed 19.5 (August 2006): 566-572.
PMID
16598695
Source
pubmed
Published In
Nmr in Biomedicine
Volume
19
Issue
5
Publish Date
2006
Start Page
566
End Page
572
DOI
10.1002/nbm.1035

Single-voxel 1H PRESS at 4.0 T: precision and variability of measurements in anterior cingulate and hippocampus.

The precision [coefficient of variation or CV (%) = 100SD/X] of single-voxel point resolved spectroscopic data was characterized bilaterally, in anterior cingulate and in hippocampus, at 4.0 T in a healthy subject. Data acquisition was replicated 10 times after voxel repositioning and readjusting higher order shims. Precision measurements show that the scan-to-scan precision is better in anterior cingulate than in hippocampus, with an average CV of 9.2% (for total NAA, tCho and Cr) in anterior cingulate and 13.9% in hippocampus. Variability measurements made by the same method in 24 healthy subjects and in 29 schizophrenia patients showed that there is substantial biological variability in metabolite levels, even in healthy subjects. Simple calculations suggest that more than 200 subjects would be needed to detect a 5% difference in NAA between patients and controls.

Authors
Venkatraman, TN; Hamer, RM; Perkins, DO; Song, AW; Lieberman, JA; Steen, RG
MLA Citation
Venkatraman, TN, Hamer, RM, Perkins, DO, Song, AW, Lieberman, JA, and Steen, RG. "Single-voxel 1H PRESS at 4.0 T: precision and variability of measurements in anterior cingulate and hippocampus." NMR Biomed 19.4 (June 2006): 484-491.
PMID
16763968
Source
pubmed
Published In
Nmr in Biomedicine
Volume
19
Issue
4
Publish Date
2006
Start Page
484
End Page
491
DOI
10.1002/nbm.1055

Synchronized detection of minute electrical currents with MRI using Lorentz effect imaging.

The blood oxygenation level-dependent (BOLD) effect is the most commonly used contrast mechanism in functional magnetic resonance imaging (fMRI), due to its relatively high spatial resolution and sensitivity. However, the ability of BOLD fMRI to accurately localize neuronal activation in space and time is limited by the inherent hemodynamic modulation. There is hence a need to develop alternative MRI methods that can directly image neuroelectric activity, thereby achieving both a high temporal resolution and spatial specificity as compared to conventional BOLD fMRI. In this paper, we extend the Lorentz effect imaging technique, which can detect spatially incoherent yet temporally synchronized minute electrical activity in a strong magnetic field, and demonstrate its feasibility for imaging randomly oriented electrical currents on the order of microamperes with a temporal resolution on the order of milliseconds in gel phantoms. This constitutes a promising step towards its application to direct imaging of neuroelectric activity in vivo, which has the same order of current density and temporal synchrony.

Authors
Truong, T-K; Wilbur, JL; Song, AW
MLA Citation
Truong, T-K, Wilbur, JL, and Song, AW. "Synchronized detection of minute electrical currents with MRI using Lorentz effect imaging." J Magn Reson 179.1 (March 2006): 85-91.
PMID
16343959
Source
pubmed
Published In
Journal of Magnetic Resonance
Volume
179
Issue
1
Publish Date
2006
Start Page
85
End Page
91
DOI
10.1016/j.jmr.2005.11.012

Correction for direction-dependent distortions in diffusion tensor imaging using matched magnetic field maps.

Diffusion tensor imaging (DTI) has seen increased usage in clinical and basic science research in the past decade. By assessing the water diffusion anisotropy within biological tissues, e.g. brain, researchers can infer different fiber structures important for neural pathways. A typical DTI data set contains at least one base image and six diffusion-weighted images along non-collinear encoding directions. The resultant images can then be combined to derive the three principal axes of the diffusion tensor and their respective cross terms, which can in turn be used to compute fractional anisotropy (FA) maps, apparent diffusion coefficient (ADC) maps, and to construct axonal fibers. The above operations all assume that DTI images along different diffusion-weighting directions for the same brain register to each other without spatial distortions. This assumption is generally false, as the large diffusion-weighting gradients would usually induce eddy currents to generate diffusion-weighting direction-dependent field gradients, leading to mis-registration within the DTI data set. Traditional methods for correcting magnetic field-induced distortions do not usually take into account these direction-dependent eddy currents unique for DTI, and they are usually time-consuming because multiple phase images need to be acquired. In this report, we describe our theory and implementation of an efficient and effective method to correct for the main field and eddy current-induced direction-dependent distortions for DTI images under a unified framework to facilitate the daily practice of DTI acquisitions.

Authors
Chen, B; Guo, H; Song, AW
MLA Citation
Chen, B, Guo, H, and Song, AW. "Correction for direction-dependent distortions in diffusion tensor imaging using matched magnetic field maps." Neuroimage 30.1 (March 2006): 121-129.
PMID
16242966
Source
pubmed
Published In
NeuroImage
Volume
30
Issue
1
Publish Date
2006
Start Page
121
End Page
129
DOI
10.1016/j.neuroimage.2005.09.008

Decisions under uncertainty: probabilistic context influences activation of prefrontal and parietal cortices.

Many decisions are made under uncertainty; that is, with limited information about their potential consequences. Previous neuroimaging studies of decision making have implicated regions of the medial frontal lobe in processes related to the resolution of uncertainty. However, a different set of regions in dorsal prefrontal and posterior parietal cortices has been reported to be critical for selection of actions to unexpected or unpredicted stimuli within a sequence. In the current study, we induced uncertainty using a novel task that required subjects to base their decisions on a binary sequence of eight stimuli so that uncertainty changed dynamically over time (from 20 to 50%), depending on which stimuli were presented. Activation within prefrontal, parietal, and insular cortices increased with increasing uncertainty. In contrast, within medial frontal regions, as well as motor and visual cortices, activation did not increase with increasing uncertainty. We conclude that the brain response to uncertainty depends on the demands of the experimental task. When uncertainty depends on learned associations between stimuli and responses, as in previous studies, it modulates activation in the medial frontal lobes. However, when uncertainty develops over short time scales as information is accumulated toward a decision, dorsal prefrontal and posterior parietal contributions are critical for its resolution. The distinction between neural mechanisms subserving different forms of uncertainty resolution provides an important constraint for neuroeconomic models of decision making.

Authors
Huettel, SA; Song, AW; McCarthy, G
MLA Citation
Huettel, SA, Song, AW, and McCarthy, G. "Decisions under uncertainty: probabilistic context influences activation of prefrontal and parietal cortices." J Neurosci 25.13 (March 30, 2005): 3304-3311.
PMID
15800185
Source
pubmed
Published In
The Journal of neuroscience : the official journal of the Society for Neuroscience
Volume
25
Issue
13
Publish Date
2005
Start Page
3304
End Page
3311
DOI
10.1523/JNEUROSCI.5070-04.2005

Amygdala activation to sad pictures during high-field (4 tesla) functional magnetic resonance imaging.

Fear-related processing in the amygdala has been well documented, but its role in signaling other emotions remains controversial. The authors recovered signal loss in the amygdala at high-field strength using an inward spiral pulse sequence and probed its response to pictures varying in their degree of portrayed sadness. These pictures were presented as intermittent task-irrelevant distractors during a concurrent visual oddball task. Relative to neutral distractors, sad distractors elicited greater activation along ventral brain regions, including the amygdala, fusiform gyrus, and inferior frontal gyrus. In contrast, oddball targets engaged dorsal sectors of frontal, parietal, and cingulate cortices. The amygdala's role in emotional evaluation thus extends to images of grief and despair as well as to those depicting violence and threat.

Authors
Wang, L; McCarthy, G; Song, AW; Labar, KS
MLA Citation
Wang, L, McCarthy, G, Song, AW, and Labar, KS. "Amygdala activation to sad pictures during high-field (4 tesla) functional magnetic resonance imaging." Emotion 5.1 (March 2005): 12-22.
PMID
15755216
Source
pubmed
Published In
Emotion
Volume
5
Issue
1
Publish Date
2005
Start Page
12
End Page
22
DOI
10.1037/1528-3542.5.1.12

Nonuniform activity of human calf muscles during an exercise task

Objectives: To determine the distribution of leg muscle activity during heel raises using magnetic resonance imaging (MRI) with special emphasis on quantifying activity across multiple axial sections and to determine if there are differences among portions of active muscles. Design: Pre- and postexercise (heel raise) T2-weighted time measurements were assessed by using repeated-measures analysis of variance (ANOVA) and t tests. Setting: Laboratory and MRI suites. Participants: Eight healthy volunteers. Intervention: Unilateral heel raises every 2 seconds for at least 60 seconds. Main Outcome Measures: Percentage changes from T2-weighted magnetic resonance images of the lateral gastrocnemius, medial gastrocnemius, peroneus longus, soleus, and tibialis anterior muscles, across 10 axial sections, exercise bouts, and a pre-exercise condition. Results: The lateral gastrocnemius, medial gastrocnemius, peroneus longus, and soleus had significantly larger changes in T2 time from pre-exercise times than did the tibialis anterior for whole muscles as determined by using repeated-measures ANOVA and post hoc analyses. The medial gastrocnemius had a significantly greater change in T2 time than the lateral gastrocnemius. Proximal axial sections of the lateral gastrocnemius, medial gastrocnemius, and soleus had significantly larger changes in T2 time from pre-exercise than did distal sections. Conclusions: This work reconfirms that multiple muscles contribute to plantarflexor forces and additionally shows an apparent proximal versus subvolume organization of activity within the gastrocnemius, medial gastrocnemius, and soleus but not the peroneus longus. This proximal versus distal organization of muscle activity needs further investigation. There may be clinical implications for therapeutic interventions that require accurate placement of electrodes such as biofeedback. © 2005 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.

Authors
Segal, RL; Song, AW
MLA Citation
Segal, RL, and Song, AW. "Nonuniform activity of human calf muscles during an exercise task." Archives of Physical Medicine and Rehabilitation 86.10 (2005): 2013-2017.
PMID
16213247
Source
scival
Published In
Archives of Physical Medicine and Rehabilitation
Volume
86
Issue
10
Publish Date
2005
Start Page
2013
End Page
2017
DOI
10.1016/j.apmr.2005.04.012

B factor dependence of the temporal characteristics of brain activation using dynamic apparent diffusion coefficient contrast.

Functional MRI studies to date have been generally performed using the blood oxygenation level dependent (BOLD) contrast mechanism. Recently, it has been proposed that dynamic change in the apparent diffusion coefficient (ADC), measured using intravoxel incoherent motion (IVIM) weighting, can be used as a robust functional contrast mechanism. Based on the differences in the timing characteristics compared to the BOLD activation, the ADC contrast can be selectively sensitized to upstream vascular pools (e.g., arterial networks). In this study we further investigated the timing characteristics of the functional ADC contrast using multiple degrees of IVIM weighting. It was found that the time course in the high b factor range lagged behind that of the low b factor range, indicating that the low b factor ADC contrast included contributions from the larger and faster moving arteries, and the smaller arterioles and capillaries downstream were reflected in the high b factor changes. These changes help confirm the arterial origin of the ADC contrast and offer a direction to improve the localization of activity to small vessel networks.

Authors
Harshbarger, TB; Song, AW
MLA Citation
Harshbarger, TB, and Song, AW. "B factor dependence of the temporal characteristics of brain activation using dynamic apparent diffusion coefficient contrast." Magn Reson Med 52.6 (December 2004): 1432-1437.
PMID
15562490
Source
pubmed
Published In
Magnetic Resonance in Medicine
Volume
52
Issue
6
Publish Date
2004
Start Page
1432
End Page
1437
DOI
10.1002/mrm.20293

Changes in magnetization transfer MRI correlate with spreading depression-induced astroglial reactivity and increased protein expression in mice.

OBJECTIVE: Gliosis refers to a range of glial cell transformations that vary according to specific brain pathologic states. Disease, however, is not a prerequisite for gliosis because glial reactivity may also be seen in regions of increased physiologic activity. Our study tests the hypothesis that high-field-strength magnetization transfer MRI is a sensitive technique for detecting transient glial reactivity after experimental spreading depression, a relatively benign perturbation unaccompanied by cell injury. MATERIALS AND METHODS: Unilateral neocortical spreading depression was elicited in mouse cerebral hemispheres and confirmed by transcranial blood flow and extracellular potential measurements. After 3 days, mice were imaged at 4 T using magnetization transfer techniques. Astroglial reactivity was determined immunohistochemically, and protein expression in control and experimental hemispheres was compared using proteomic techniques. RESULTS: Sixteen ([mean +/- SD] +/- 3) spreading depressions (n = 10) were recorded in experimental hemispheres. Spreading depression was never observed in control hemispheres. At 3 days, an 8% decrease (p < 0.05, n = 4) in magnetization transfer signal intensity was measured in experimental hemispheres, which was associated with a 37% increase (p < 0.001, n = 4) in the intensity of glial fibrillary acidic protein staining. Proteomic analysis performed 3 days after the induction of spreading depression showed upregulation of at least 56 proteins, including extracellular and intracellular elements. CONCLUSION: Magnetization transfer at 4.0-T MRI is a sensitive method for detecting glial reactivity and changes in protein expression not associated with cell injury. These results suggest magnetization transfer MRI techniques may have potential for detecting glial reactivity in physiologic processes such as learning and in early disease states.

Authors
Lascola, CD; Song, AW; Haystead, TA; Warner, DS; Verleysen, K; Freed, TA; Provenzale, JM
MLA Citation
Lascola, CD, Song, AW, Haystead, TA, Warner, DS, Verleysen, K, Freed, TA, and Provenzale, JM. "Changes in magnetization transfer MRI correlate with spreading depression-induced astroglial reactivity and increased protein expression in mice." AJR Am J Roentgenol 183.6 (December 2004): 1791-1797.
PMID
15547231
Source
pubmed
Published In
AJR. American journal of roentgenology
Volume
183
Issue
6
Publish Date
2004
Start Page
1791
End Page
1797
DOI
10.2214/ajr.183.6.01831791

The BOLD fMRI refractory effect is specific to stimulus attributes: evidence from a visual motion paradigm.

Functional magnetic resonance imaging (fMRI) studies have demonstrated that the blood oxygenation level-dependent (BOLD) hemodynamic response (HDR) to a stimulus is reduced by the previous presentation of a similar stimulus. We investigated the dependence of this refractory effect upon stimulus characteristics using a novel adaptation paradigm while scanning subjects using fMRI at 4 T. The stimuli were composed of horizontal stripes that scrolled up, scrolled down, or remained static, randomly presented for 1-s duration with stimulus-onset asynchronies (SOAs) of 2-7 s. We identified regions of interest (ROI) in lateral temporal--occipital cortex that were activated by motion stimuli, regardless of direction or SOA. We found strong evidence for direction specificity in motion-sensitive lateral temporal-occipital (LTO) cortex. For stimuli whose direction of motion reprised that of the previous stimulus (e.g., up preceded by up), the fMRI response was attenuated at short SOAs (2-4 s) compared to long SOAs (5-7 s). However, for stimuli whose direction of motion was opposite that of the previous stimulus (e.g., up preceded by down), little or no refractory effect was observed. Additionally, examination of activity in pericalcarine cortex indicated a similar pattern. We conclude that the fMRI refractory effect predominantly reflects local stimulus-specific neuronal or neurovascular adaptation and is unlikely to be a nonspecific response of large vessels that support broad functional regions.

Authors
Huettel, SA; Obembe, OO; Song, AW; Woldorff, MG
MLA Citation
Huettel, SA, Obembe, OO, Song, AW, and Woldorff, MG. "The BOLD fMRI refractory effect is specific to stimulus attributes: evidence from a visual motion paradigm." Neuroimage 23.1 (September 2004): 402-408.
PMID
15325388
Source
pubmed
Published In
NeuroImage
Volume
23
Issue
1
Publish Date
2004
Start Page
402
End Page
408
DOI
10.1016/j.neuroimage.2004.04.031

The spatial and temporal characteristics of the apparent-diffusion-coefficient-dependent fMRI signal changes during visual stimulation.

The blood oxygenation level dependent (BOLD) contrast has been commonly used to detect fMRI signal. The majority of the BOLD signals are believed to arise from the venous and capillary networks. However, only those from the capillaries are spatially close to the neuronal activities, while the signals from large veins could be distant, rendering the overall localization inaccurate. In recent years, an alternative contrast using arterial spin labeled (ASL) perfusion imaging techniques has been proposed for predominant capillary sensitivity. Such acquisition methods, however, are intrinsically limited in temporal resolution and spatial coverage. Another contrast mechanism, free of such constraints, is based on the apparent diffusion coefficient (ADC) changes during brain activation using isotropic diffusion weighting. It has been shown that these changes are synchronized with brain activation and that they, as a whole, temporally precede BOLD activation, suggesting significant upstream arterial contribution. Moreover, the spatial overlaps between the upstream ADC and downstream BOLD activations are shown to be more localized in the capillaries, which are the temporal and spatial middle ground. In this paper, we sought to further investigate the temporal and spatial characteristics of ADC contrast with additional arterial signal suppression. Also, a pixel-based evaluation was performed in conjunction with the averaged global assessment. It was found that in addition to the known spatial discrepancy and global timing advance compared to the BOLD signal, the ADC activation endured significant temporal heterogeneities. Such fine spatial and temporal assessment could help characterize the exact signal sources of ADC contrast, and ultimately achieve exclusive capillary sensitivity.

Authors
Song, AW; Gangstead, SL
MLA Citation
Song, AW, and Gangstead, SL. "The spatial and temporal characteristics of the apparent-diffusion-coefficient-dependent fMRI signal changes during visual stimulation." J Neural Eng 1.1 (March 2004): 32-38.
PMID
15876620
Source
pubmed
Published In
Journal of Neural Engineering
Volume
1
Issue
1
Publish Date
2004
Start Page
32
End Page
38
DOI
10.1088/1741-2560/1/1/005

Hemodynamic correlates of stimulus repetition in the visual and auditory cortices: an fMRI study.

We examined the effects of stimulus repetition upon the evoked hemodynamic response (HDR) in auditory and visual cortices measured by magnetic resonance imaging in two experiments. Experiment 1 focused on the effects of the interval duration between two identical stimuli on HDR. Pure auditory tones (1000 Hz) of 100-ms duration were presented singly or in pairs with intrapair intervals (IPIs: onset-to-onset) of 1, 4, and 6 s. In Experiment 2, using a within-subject design, we aimed to compare the HDR refractory period in both sensory cortices as well as the HDRs to auditory and visual stimuli. Identical auditory tone as described above and visual stimuli of 500-ms high-contrast checkerboard patterns were presented singly or in identical pairs with an IPI of 1 s. Images were acquired at 1.5 T using a gradient-echo echo-planar imaging sequence sensitive to blood oxygenation level-dependent (BOLD) contrast. Experiment 1 revealed that the HDR evoked by an auditory stimulus is followed by a refractory period of 4-6 s in the auditory cortex, as indicated by smaller HDR amplitudes to the second of each pair of stimuli. Furthermore, peak latency was dependent upon IPI, with longer latencies observed for shorter IPIs. Experiment 2 revealed that the HDR evoked in both sensory cortices by paired stimulus presentations is suppressed and delayed similarly by the refractory effects imposed by the preceding stimulus, suggesting similar refractory properties of the HDR at this specific IPI. We also provide evidence for additional neural resource allocation in response to repeated stimuli.

Authors
Inan, S; Mitchell, T; Song, A; Bizzell, J; Belger, A
MLA Citation
Inan, S, Mitchell, T, Song, A, Bizzell, J, and Belger, A. "Hemodynamic correlates of stimulus repetition in the visual and auditory cortices: an fMRI study." Neuroimage 21.3 (March 2004): 886-893.
PMID
15006655
Source
pubmed
Published In
NeuroImage
Volume
21
Issue
3
Publish Date
2004
Start Page
886
End Page
893
DOI
10.1016/j.neuroimage.2003.10.029

Linking hemodynamic and electrophysiological measures of brain activity: evidence from functional MRI and intracranial field potentials.

We investigated the relation between electrophysiological and hemodynamic measures of brain activity through comparison of intracranially recorded event-related local field potentials (ERPs) and blood-oxygenation level dependent functional magnetic resonance imaging (BOLD fMRI). We manipulated the duration of visual checkerboard stimuli across trials and measured stimulus-duration-related changes in ERP and BOLD activity in three brain regions: peri-calcarine cortex, the fusiform gyrus and lateral temporal-occipital (LTO) cortex. ERPs were recorded from patients who had indwelling subdural electrodes as part of presurgical testing, while BOLD responses were measured in similar brain regions in a second set of subjects. Similar BOLD responses were measured in peri-calcarine and fusiform regions, with both showing monotonic but non-linear increases in hemodynamic amplitude with stimulus duration. In sharp contrast, very different ERP responses were observed in these same regions, such that calcarine electrodes exhibited onset potentials, sustained activity over the course of stimulus duration and prominent offset potentials, while fusiform electrodes only exhibited onset potentials that did not vary with stimulus duration. No duration-related ERP or BOLD changes were observed in LTO. Additional analyses revealed no consistent changes in the EEG spectrum across different brain sites that correlated with duration-related changes in the BOLD response. We conclude that the relation between ERPs and fMRI differs across brain regions.

Authors
Huettel, SA; McKeown, MJ; Song, AW; Hart, S; Spencer, DD; Allison, T; McCarthy, G
MLA Citation
Huettel, SA, McKeown, MJ, Song, AW, Hart, S, Spencer, DD, Allison, T, and McCarthy, G. "Linking hemodynamic and electrophysiological measures of brain activity: evidence from functional MRI and intracranial field potentials." Cereb Cortex 14.2 (February 2004): 165-173.
PMID
14704213
Source
pubmed
Published In
Cerebral Cortex
Volume
14
Issue
2
Publish Date
2004
Start Page
165
End Page
173

Functional parcellation of attentional control regions of the brain.

Recently, a number of investigators have examined the neural loci of psychological processes enabling the control of visual spatial attention using cued-attention paradigms in combination with event-related functional magnetic resonance imaging. Findings from these studies have provided strong evidence for the involvement of a fronto-parietal network in attentional control. In the present study, we build upon this previous work to further investigate these attentional control systems. In particular, we employed additional controls for nonattentional sensory and interpretative aspects of cue processing to determine whether distinct regions in the fronto-parietal network are involved in different aspects of cue processing, such as cue-symbol interpretation and attentional orienting. In addition, we used shorter cue-target intervals that were closer to those used in the behavioral and event-related potential cueing literatures. Twenty participants performed a cued spatial attention task while brain activity was recorded with functional magnetic resonance imaging. We found functional specialization for different aspects of cue processing in the lateral and medial subregions of the frontal and parietal cortex. In particular, the medial subregions were more specific to the orienting of visual spatial attention, while the lateral subregions were associated with more general aspects of cue processing, such as cue-symbol interpretation. Additional cue-related effects included differential activations in midline frontal regions and pretarget enhancements in the thalamus and early visual cortical areas.

Authors
Woldorff, MG; Hazlett, CJ; Fichtenholtz, HM; Weissman, DH; Dale, AM; Song, AW
MLA Citation
Woldorff, MG, Hazlett, CJ, Fichtenholtz, HM, Weissman, DH, Dale, AM, and Song, AW. "Functional parcellation of attentional control regions of the brain." J Cogn Neurosci 16.1 (January 2004): 149-165.
Website
http://hdl.handle.net/10161/6926
PMID
15006044
Source
pubmed
Published In
Journal of Cognitive Neuroscience
Volume
16
Issue
1
Publish Date
2004
Start Page
149
End Page
165
DOI
10.1162/089892904322755638

FMRI signal source analysis using diffusion-weighted spiral-in acquisition

Despite the tremendous growth in functional magnetic resonance imaging (fMRI), susceptibility induced static field inhomogeneity at air/tissue interface have limited the study of ventral brain regions engaged in object recognition and other processes. Furthermore, the spatial extent of fMRI activations in this region may be obscured by contribution of large vessels distant from the precipitating neural events. In this report, a diffusion weighted spiral-in image acquisition was employed to recover fMRI signal in the ventral brain during object recognition with high temporal resolution, as well as to suppress large vessel contributions. The combined methodology of the ventral signal recovery and vascular signal reduction can thus be advantageous for fMRI investigations at the statically inhomogeneous areas.

Authors
Song, AW; Emberger, K; Michelich, CR; McCarthy, G
MLA Citation
Song, AW, Emberger, K, Michelich, CR, and McCarthy, G. "FMRI signal source analysis using diffusion-weighted spiral-in acquisition." Annual International Conference of the IEEE Engineering in Medicine and Biology - Proceedings 26 VI (2004): 4417-4420.
Source
scival
Published In
Annual International Conference of the IEEE Engineering in Medicine and Biology - Proceedings
Volume
26 VI
Publish Date
2004
Start Page
4417
End Page
4420

Fast functional brain signal changes detected by diffusion weighted fMRI.

Functional magnetic resonance imaging (fMRI) has become the method of choice in the study of system neuroscience, as evidenced by an explosion of such literature in the past decade. Contrast mechanisms based on the blood oxygenation level, volume, and flow changes have been used to non-invasively detect brain activation secondary to the neuronal activity. However, because of the hemodynamic modulations inherent in these signals, their spatial and temporal characteristics are influenced by the complex geometry and varying delivery speed of the brain vasculature. Consequently, spatial dispersions and temporal delays are commonly seen in the brain activity using fMRI. It is thus of critical importance to investigate alternative contrast mechanisms that may offer shorter temporal delays and more direct spatial localization. In light of a recent phantom study which demonstrated the possibility to detect the destructive phase addition from the spatially incoherent, yet temporally synchronized, displacements caused by the Lorentz force experienced during electrical conduction within a strong magnetic field, we seek to apply similar imaging technique to investigate the functional signal changes that may provide alternative temporal and spatial characteristics. It is found that by using heavy diffusion weighting, which is one form of displacement encoding strategies, to remove the vascular signal and sensitize the minute and incoherent displacement, one can detect fast dynamic signal changes synchronized to the task. This finding may help take an initial step toward direct non-invasive MRI detection of the neuronal activity with improved temporal accuracy.

Authors
Li, T; Song, AW
MLA Citation
Li, T, and Song, AW. "Fast functional brain signal changes detected by diffusion weighted fMRI." Magn Reson Imaging 21.8 (October 2003): 829-833.
PMID
14599532
Source
pubmed
Published In
Magnetic Resonance Imaging
Volume
21
Issue
8
Publish Date
2003
Start Page
829
End Page
833

Functional activation using apparent diffusion coefficient-dependent contrast allows better spatial localization to the neuronal activity: evidence using diffusion tensor imaging and fiber tracking.

Recent studies suggested that functional activation using apparent diffusion coefficient (ADC) contrast can be used to detect synchronized functional MRI (fMRI) signal changes during brain activation. Such changes may reflect better spatial localization to the smaller vessels, which are closely coupled to the true neuronal activation. Since it is generally believed that there are neural pathways among neuronally relevant areas, methods that would allow clear delineation of such pathways could help validate the neuronal relevance of the activated functional areas. The development of diffusion tensor imaging (DTI) has shown promise in detailed nerve fiber tracking. In this report, DTI was adopted to track the fiber connections among the discrete areas determined using the ADC contrast, in an effort to confirm the neuronal origin of these activated areas. As a comparison, activated areas using blood oxygenation level-dependent (BOLD) contrast were also obtained. Our results showed that the areas determined by the ADC contrast consistently allowed better fiber tracking within, while the BOLD-activated areas were more spatially diffused due to the smearing effect of brain vasculature, rendering the task of fiber tracking more difficult. This observation provides converging evidence that the activated areas using ADC contrast are more closely coupled to the neuronal activity than those using BOLD contrast.

Authors
Song, AW; Harshbarger, T; Li, T; Kim, K-H; Ugurbil, K; Mori, S; Kim, D-S
MLA Citation
Song, AW, Harshbarger, T, Li, T, Kim, K-H, Ugurbil, K, Mori, S, and Kim, D-S. "Functional activation using apparent diffusion coefficient-dependent contrast allows better spatial localization to the neuronal activity: evidence using diffusion tensor imaging and fiber tracking." NeuroImage 20.2 (October 2003): 955-961.
PMID
14568465
Source
epmc
Published In
NeuroImage
Volume
20
Issue
2
Publish Date
2003
Start Page
955
End Page
961
DOI
10.1016/s1053-8119(03)00292-1

Single-shot spiral image acquisition with embedded z-shimming for susceptibility signal recovery.

PURPOSE: To efficiently and effectively recover the susceptibility-induced signal losses for functional MRI (fMRI) experiments. MATERIALS AND METHODS: The signal losses near air/tissue interfaces at the ventral brain regions introduce difficulties in the neuroimaging studies concerned with brain functions such as memory, emotion, and olfaction processes. The z-shimming technique has been introduced in fMRI image acquisition to recover such losses. One significant drawback of such an approach is its time consuming nature. In this report, a single-shot spiral imaging method, which combines spiral-in and spiral-out acquisitions along with embedded z-shimming gradient, was proposed and implemented to achieve signal recovery without sacrificing temporal resolution. RESULTS: Using the proposed method, final images were shown in the ventral brain regions. The images were acquired with a throughput of 16 slices/second and demonstrated effectiveness and efficiency in signal recovery near air/tissue interfaces. CONCLUSION: Uniform recovery can be achieved efficiently near air/tissue interfaces where susceptibility-induced spatial gradients are pronounced. We anticipate that our method would be well suited for fMRI studies involving the ventral brain areas.

Authors
Guo, H; Song, AW
MLA Citation
Guo, H, and Song, AW. "Single-shot spiral image acquisition with embedded z-shimming for susceptibility signal recovery." J Magn Reson Imaging 18.3 (September 2003): 389-395.
PMID
12938139
Source
pubmed
Published In
Journal of Magnetic Resonance Imaging
Volume
18
Issue
3
Publish Date
2003
Start Page
389
End Page
395
DOI
10.1002/jmri.10355

Conflict monitoring in the human anterior cingulate cortex during selective attention to global and local object features.

Parallel processing affords the brain many advantages, but processing multiple bits of information simultaneously presents formidable challenges. For example, while one is listening to a speaker at a noisy social gathering, processing irrelevant conversations may lead to the activation of irrelevant perceptual, semantic, and response representations that conflict with those evoked by the speaker. In these situations, specialized brain systems may be recruited to detect and resolve conflict before it leads to incorrect perception and/or behavior. Consistent with this view, recent findings indicate that dorsal/caudal anterior cingulate cortex (dACC), on the medial walls of the frontal lobes, detects conflict between competing motor responses primed by relevant versus irrelevant stimuli. Here, we used a cued global/local selective attention task to investigate whether the dACC plays a general role in conflict detection that includes monitoring for conflicting perceptual or semantic representations. Using event-related functional magnetic resonance imaging (fMRI), we found that the dACC was activated by response conflict in both the global and the local task, consistent with results from prior studies. However, dACC was also activated by perceptual and semantic conflict arising from global distracters during the local task. The results from the local task have implications for recent theories of attentional control in which the dACC's contribution to conflict monitoring is limited to response stages of processing, as well as for our understanding of clinical disorders in which disruptions of attention are associated with dACC dysfunction.

Authors
Weissman, DH; Giesbrecht, B; Song, AW; Mangun, GR; Woldorff, MG
MLA Citation
Weissman, DH, Giesbrecht, B, Song, AW, Mangun, GR, and Woldorff, MG. "Conflict monitoring in the human anterior cingulate cortex during selective attention to global and local object features." Neuroimage 19.4 (August 2003): 1361-1368.
PMID
12948694
Source
pubmed
Published In
NeuroImage
Volume
19
Issue
4
Publish Date
2003
Start Page
1361
End Page
1368

Neural mechanisms of top-down control during spatial and feature attention.

Theories of visual selective attention posit that both spatial location and nonspatial stimulus features (e.g., color) are elementary dimensions on which top-down attentional control mechanisms can selectively influence visual processing. Neuropsychological and neuroimaging studies have demonstrated that regions of superior frontal and parietal cortex are critically involved in the control of visual-spatial attention. This frontoparietal control network has also been found to be activated when attention is oriented to nonspatial stimulus features (e.g., motion). To test the generality of the frontoparietal network in attentional control, we directly compared spatial and nonspatial attention in a cuing paradigm. Event-related fMRI methods permitted the isolation of attentional control activity during orienting to a location or to a nonspatial stimulus feature (color). Portions of the frontoparietal network were commonly activated to the spatial and nonspatial cues. However, direct statistical comparisons of cue-related activity revealed subregions of the frontoparietal network that were significantly more active during spatial than nonspatial orienting when all other stimulus, task, and attentional factors were equated. No regions of the frontal-parietal network were more active for nonspatial cues in comparison to spatial cues. These findings support models suggesting that subregions of the frontal-parietal network are highly specific for controlling spatial selective attention.

Authors
Giesbrecht, B; Woldorff, MG; Song, AW; Mangun, GR
MLA Citation
Giesbrecht, B, Woldorff, MG, Song, AW, and Mangun, GR. "Neural mechanisms of top-down control during spatial and feature attention." Neuroimage 19.3 (July 2003): 496-512.
PMID
12880783
Source
pubmed
Published In
NeuroImage
Volume
19
Issue
3
Publish Date
2003
Start Page
496
End Page
512

An improved gridding method for spiral MRI using nonuniform fast Fourier transform.

The algorithm of Liu and Nguyen [IEEE Microw. Guided Wave Lett. 8 (1) (1998) 18; SIAM J. Sci. Comput. 21 (1) (1999) 283] for nonuniform fast Fourier transform (NUFFT) has been extended to two dimensions to reconstruct images using spiral MRI. The new gridding method, called LS_NUFFT, minimizes the reconstruction approximation error in the Least Square sense by generated convolution kernels that fit for the spiral k-space trajectories. For analytical comparison, the LS_NUFFT has been fitted into a consistent framework with the conventional gridding methods using Kaiser-Bessel gridding and a recently proposed generalized FFT (GFFT) approach. Experimental comparison was made by assessing the performance of the LS_NUFFT with that of the standard direct summation method and the Kaiser-Bessel gridding method, using both digital phantom data and in vivo experimental data. Because of the explicitly optimized convolution kernel in LS_NUFFT, reconstruction results showed that the LS_NUFFT yields smaller reconstruction approximation error than the Kaiser-Bessel gridding method, but with the same computation complexity.

Authors
Sha, L; Guo, H; Song, AW
MLA Citation
Sha, L, Guo, H, and Song, AW. "An improved gridding method for spiral MRI using nonuniform fast Fourier transform." J Magn Reson 162.2 (June 2003): 250-258.
PMID
12810009
Source
pubmed
Published In
Journal of Magnetic Resonance
Volume
162
Issue
2
Publish Date
2003
Start Page
250
End Page
258

Improved spatial localization based on flow-moment-nulled and intra-voxel incoherent motion-weighted fMRI.

Functional MRI signal based on the blood oxygenation level-dependent contrast can reveal brain vascular activities secondary to neuronal activation. It could, however, arise from vascular compartments of all sizes, and in particular, be largely influenced by contributions of large vein origins that are distant from the neuronal activities. Alternative contrasts can be generated based on the cerebral blood flow or volume changes that would provide complementary information to help achieve more accurate localization to the small vessel origins. Recent reports also indicated that apparent diffusion coefficient-based contrast using intravoxel incoherent motion (IVIM) weighting could be used to efficiently detect synchronized signal changes with the functional activities. It was found that this contrast has significant arterial contribution where flow changes are more dominant. In this study, a refined approach was proposed that incorporated the flow-moment-nulling (FMN) strategy to study signal changes from the brain activation. The results were then compared with those from conventional IVIM- and BOLD-weighted acquisitions. It was shown that the activated region using the new acquisition strategy had smaller spatial extent, which was contained within the activated areas from the other two methods. Based on the known characteristics of the conventional IVIM and BOLD contrasts, it was inferred that the FMN-IVIM acquisition had improved selective sensitivity towards smaller vessels where volume changes were prevalent. Therefore, such an acquisition method may provide more specific spatial localization closely coupled to the true neuronal activities.

Authors
Song, AW; Li, T
MLA Citation
Song, AW, and Li, T. "Improved spatial localization based on flow-moment-nulled and intra-voxel incoherent motion-weighted fMRI." NMR Biomed 16.3 (May 2003): 137-143.
PMID
12884357
Source
pubmed
Published In
Nmr in Biomedicine
Volume
16
Issue
3
Publish Date
2003
Start Page
137
End Page
143
DOI
10.1002/nbm.819

Faces evoke spatially differentiated patterns of BOLD activation and deactivation

Using fMRI techniques sensitive to blood oxygen-level dependent (BOLD) contrast, we measured brain activity in participants (n = 8) as they viewed images of faces presented periodically within a continuously changing montage of common objects. Consistent with prior studies, we identified regions of ventral extrastriate cortex, primarily in the fusiform and inferior temporal gyri and nearby cortex, that were activated by faces as measured by an increase in BOLD signal. In addition, we made the novel observation that faces deactivated other areas of ventral extrastriate cortex, primarily in the lingual and parahippocampal gyri and medial to activations. These deactivated regions, identified by a decrease in BOLD signal, may reflect populations of neurons that decrease their activity when faces appear, possibly as a consequence of category-specific inhibition. © 2003 Lippincott Williams & Wilkins.

Authors
Pelphrey, KA; Mack, PB; Song, A; Güzeldere, G; McCarthy, G
MLA Citation
Pelphrey, KA, Mack, PB, Song, A, Güzeldere, G, and McCarthy, G. "Faces evoke spatially differentiated patterns of BOLD activation and deactivation." NeuroReport 14.7 (2003): 955-959.
Website
http://hdl.handle.net/10161/6962
PMID
12802182
Source
scival
Published In
NeuroReport
Volume
14
Issue
7
Publish Date
2003
Start Page
955
End Page
959

Word frequency and subsequent memory effects studied using event-related fMRI

Event-related fMRI was used to evaluate the effect of printed word frequency on the subsequent recognition of words incidentally encoded while 16 healthy right-handed volunteers performed living/nonliving judgments. Semantic judgment took longer for low-frequency words. These words were more accurately recognized than high-frequency words at later testing. Low-frequency words were also associated with relatively greater left prefrontal, left fusiform gyrus, and anterior cingulate activation. Words that were subsequently recognized were associated with greater activation in the left prefrontal region compared to those that were forgotten. These findings suggest the specific brain regions where less commonly encountered words are processed in a manner that facilitates their subsequent recognition. © 2003 Elsevier Inc. All rights reserved.

Authors
Chee, MWL; Westphal, C; Goh, J; Graham, S; Song, AW
MLA Citation
Chee, MWL, Westphal, C, Goh, J, Graham, S, and Song, AW. "Word frequency and subsequent memory effects studied using event-related fMRI." NeuroImage 20.2 (2003): 1042-1051.
PMID
14568474
Source
scival
Published In
NeuroImage
Volume
20
Issue
2
Publish Date
2003
Start Page
1042
End Page
1051
DOI
10.1016/S1053-8119(03)00335-5

Magnetic resonance imaging with lateralized arterial spin labeling.

We report the development of a new MRI technique which allows spins from right-sided arteries to be labeled separately from spins from left-sided arteries. This method uses two spatially-selective adiabatic inversion pulses to alternate the labeling of the right carotid and vertebral artery separate from the left carotid and vertebral artery. Normal volunteers were scanned on a clinical 1.5 T system and the resultant brain images correlated with the T2 anatomic images. Arterial anatomy was depicted using the new sequence and corresponded to the labeling scheme employed by the sequence. It was demonstrated that spatially selective inversion pulses permit the encoding of the spins within specific vascular origins and the observation of their run-off territory.

Authors
Eastwood, JD; Holder, CA; Hudgins, PA; Song, AW
MLA Citation
Eastwood, JD, Holder, CA, Hudgins, PA, and Song, AW. "Magnetic resonance imaging with lateralized arterial spin labeling." Magn Reson Imaging 20.8 (October 2002): 583-586.
PMID
12467864
Source
pubmed
Published In
Magnetic Resonance Imaging
Volume
20
Issue
8
Publish Date
2002
Start Page
583
End Page
586

Enhanced spatial localization of neuronal activation using simultaneous apparent-diffusion-coefficient and blood-oxygenation functional magnetic resonance imaging.

Functional MRI (fMRI) can detect blood oxygenation level dependent (BOLD) hemodynamic responses secondary to local neuronal activity. The most commonly used method for detecting fMRI signals is the gradient-echo echo-planar imaging (EPI) technique because of its sensitivity and speed. However, it is known that much of the signal obtained with this approach arises from large veins, with additional contribution from the capillaries and venules. Early experiments using diffusion-weighted gradient-echo EPI have suggested that intravoxel incoherent motion (IVIM) weighting can selectively attenuate contributions from large vessels based on the differences in the mobility of the blood within them, thereby revealing the contributions from hemodynamic changes in capillaries, which are in close spatial proximity to the activated neural tissue. Using this differential sensitivity of the various neurovascular compartments to IVIM weighting, we present a new approach for deriving functional maps of neural activity. This method is based on task-induced changes of the apparent diffusion coefficients (ADC), a signal that we demonstrate is generated in vascular compartments that only partially overlap with those generating the BOLD signal. The approach allows both the ADC-based maps and the more commonly used BOLD-based maps to be acquired simultaneously. The spatial overlap between these maps can be used to create composite maps that permit improved localization of the underlying neuronal activity patterns by identifying signals generated in those vascular components that are in closest proximity to the active neuronal populations of interest.

Authors
Song, AW; Woldorff, MG; Gangstead, S; Mangun, GR; McCarthy, G
MLA Citation
Song, AW, Woldorff, MG, Gangstead, S, Mangun, GR, and McCarthy, G. "Enhanced spatial localization of neuronal activation using simultaneous apparent-diffusion-coefficient and blood-oxygenation functional magnetic resonance imaging." Neuroimage 17.2 (October 2002): 742-750.
PMID
12377149
Source
pubmed
Published In
NeuroImage
Volume
17
Issue
2
Publish Date
2002
Start Page
742
End Page
750

BOLD signal compartmentalization based on the apparent diffusion coefficient.

Functional MRI (fMRI) can detect blood oxygenation level dependent (BOLD) hemodynamic responses secondary to neuronal activity. The most commonly used method for detecting fMRI signals is the gradient-echo echo-planar imaging (EPI) technique because of its sensitivity and speed. However, it is generally believed that a significant portion of these signals arises from large veins, with additional contribution from the capillaries and parenchyma. Early experiments using diffusion-weighted gradient-echo EPI have suggested that intra-voxel incoherent motion (IVIM) weighting inherent in the sequence can selectively attenuate contributions from different vessels based on the differences in the mobility of the blood within them. In the present study, we used similar approach to characterize the apparent diffusion coefficient (ADC) distribution within the activated areas of BOLD contrast. It is shown that the voxel values of the ADCs obtained from this technique can infer various vascular contributions to the BOLD signal.

Authors
Song, AW; Fichtenholtz, H; Woldorff, M
MLA Citation
Song, AW, Fichtenholtz, H, and Woldorff, M. "BOLD signal compartmentalization based on the apparent diffusion coefficient." Magn Reson Imaging 20.7 (September 2002): 521-525.
Website
http://hdl.handle.net/10161/6935
PMID
12413597
Source
pubmed
Published In
Magnetic Resonance Imaging
Volume
20
Issue
7
Publish Date
2002
Start Page
521
End Page
525

On the timing characteristics of the apparent diffusion coefficient contrast in fMRI.

For the past 10 years, functional MRI (fMRI) has seen rapid progress in both clinical and basic science research. Most of the imaging techniques are based on the blood oxygenation level-dependent (BOLD) contrast which arises from the field perturbation of the paramagnetic deoxyhemoglobin due to the mismatch between the local oxygen demand and delivery. Because the changes of oxygenation level take place mostly in the veins, the dominant signal sources of the BOLD signal are intra- and extravascular proton pools of the veins. Perfusion imaging methods, developed parallel to the BOLD technique, seek to quantify the blood flow and perfusion. Recently, perfusion imaging using arterial spin tagging methods have been used to study brain function by investigating the changes of the blood flow and perfusion during brain activation, thereby generating an alternative contrast mechanism to the functional brain imaging. Since most of these methods require tagging pulse and wait time for blood to be delivered to the imaged slice, the temporal resolution may not be optimal. Dynamic intravoxel incoherent motion (IVIM) weighting schemes using apparent diffusion coefficient (ADC) contrast were suggested to image the relative changes of the in-plane blood flow during brain function. In this report, it was demonstrated that, in addition to the spatial discrepancies of the activated areas, the time course based on the ADC contrast consistently precedes that from the BOLD contrast with timing offset on the order of 1 sec. Since arterial networks would have different spatial locations and preceding temporal characters, the findings in this report are indicative that the ADC contrast is sensitive to the arterial blood flow changes.

Authors
Gangstead, SL; Song, AW
MLA Citation
Gangstead, SL, and Song, AW. "On the timing characteristics of the apparent diffusion coefficient contrast in fMRI." Magn Reson Med 48.2 (August 2002): 385-388.
PMID
12210948
Source
pubmed
Published In
Magnetic Resonance in Medicine
Volume
48
Issue
2
Publish Date
2002
Start Page
385
End Page
388
DOI
10.1002/mrm.10189

Experience-dependent changes in cerebellar contributions to motor sequence learning

Studies in experimental animals and humans have stressed the role of the cerebellum in motor skill learning. Yet, the relative importance of the cerebellar cortex and deep nuclei, as well as the nature of the dynamic functional changes occurring between these and other motor-related structures during learning, remains in dispute. Using functional magnetic resonance imaging and a motor sequence learning paradigm in humans, we found evidence of an experience-dependent shift of activation from the cerebellar cortex to the dentate nucleus during early learning, and from a cerebellar-cortical to a striatal-cortical network with extended practice. The results indicate that intrinsic modulation within the cerebellum, in concert with activation of motor-related cortical regions, serves to set up a procedurally acquired sequence of movements that is then maintained elsewhere in the brain.

Authors
Doyon, J; Song, AW; Karni, A; Lalonde, F; Adams, MM; Ungerleider, LG
MLA Citation
Doyon, J, Song, AW, Karni, A, Lalonde, F, Adams, MM, and Ungerleider, LG. "Experience-dependent changes in cerebellar contributions to motor sequence learning." Proceedings of the National Academy of Sciences of the United States of America 99.2 (2002): 1017-1022.
PMID
11805340
Source
scival
Published In
Proceedings of the National Academy of Sciences of the United States of America
Volume
99
Issue
2
Publish Date
2002
Start Page
1017
End Page
1022
DOI
10.1073/pnas.022615199

Single-shot EPI with signal recovery from the susceptibility-induced losses.

A major problem in the gradient-recalled echo-planar imaging (EPI) method that also uses a long echo time (TE) is the severe signal loss in regions with large static field inhomogeneities. These regions include the ventral frontal, medial temporal, and inferior temporal lobes, which experience inhomogeneities induced by susceptibility effects commonly found near air/tissue interfaces. For functional magnetic resonance imaging (fMRI) studies that use both gradient-recalled EPI at relatively long TE and high-field scanners, this signal loss is severe, preventing investigation of certain human cognitive processes that involve these regions, such as memory and attention. Methods have been developed to recover this signal loss; however, most of them require multiple excitations and thus compromise temporal resolution. In this report, a new technique is described which achieves good signal recovery within a single excitation. It is anticipated that this technique will prove useful for fMRI studies in inhomogeneous areas that require high temporal resolution.

Authors
Song, AW
MLA Citation
Song, AW. "Single-shot EPI with signal recovery from the susceptibility-induced losses." Magn Reson Med 46.2 (August 2001): 407-411.
PMID
11477647
Source
pubmed
Published In
Magnetic Resonance in Medicine
Volume
46
Issue
2
Publish Date
2001
Start Page
407
End Page
411

Lorentz effect imaging.

This paper presents a method that can detect minute electrical activity in a strong magnetic field. It uses displacement encoding to detect small spatial displacement induced by Lorentz force on the conducting materials, hence the term Lorentz effect imaging (LEI). With increased sensitivity from improved hardware capabilities or signal averaging, this technique may be used to detect spatial displacements induced by small currents comparable to neuronal electrical current. The initial results using the LEI technique may provide insight in assessing the feasibility of using MRI to non-invasively detect the neuronal electrical activities.

Authors
Song, AW; Takahashi, AM
MLA Citation
Song, AW, and Takahashi, AM. "Lorentz effect imaging." Magn Reson Imaging 19.6 (July 2001): 763-767.
PMID
11551715
Source
pubmed
Published In
Magnetic Resonance Imaging
Volume
19
Issue
6
Publish Date
2001
Start Page
763
End Page
767

Linking sight and sound: fMRI evidence of primary auditory cortex activation during visual word recognition

We describe two studies that used repetition priming paradigms to investigate brain activity during the reading of single words. Functional magnetic resonance images were collected during a visual lexical decision task in which nonword stimuli were manipulated with regard to phonological properties and compared to genuine English words. We observed a region in left-hemisphere primary auditory cortex linked to a repetition priming effect. The priming effect activity was observed only for stimuli that sound like known words; moreover, this region was sensitive to strategic task differences. Thus, a brain region involved in the most basic aspects of auditory processing appears to be engaged in reading even when there is no environmental oral or auditory component. © 2001 Academic Press.

Authors
Haist, F; Song, AW; Wild, K; Faber, TL; Popp, CA; Morris, RD
MLA Citation
Haist, F, Song, AW, Wild, K, Faber, TL, Popp, CA, and Morris, RD. "Linking sight and sound: fMRI evidence of primary auditory cortex activation during visual word recognition." Brain and Language 76.3 (2001): 340-350.
PMID
11247649
Source
scival
Published In
Brain and Language
Volume
76
Issue
3
Publish Date
2001
Start Page
340
End Page
350
DOI
10.1006/brln.2000.2433

Functional activation of the extensor carpi radialis muscles in humans

Objectives: To assess activity of radial wrist extensors caused by isometric radial deviation and extension by using magnetic resonance imaging (MRI) and to assess measures that might be used to normalize T2-weighted data. Design: Two-way analysis of variance (ANOVA) design. Setting: Laboratory and children's hospital. Participants: Three healthy volunteers. Interventions: Ten repetitions of 10-second randomly ordered 30% or 60% of maximum voluntary isometric contractions toward wrist extension or radial deviation. Main Outcome Measures: Average T2 values from T2-weighted MR images of the extensor carpi radialis brevis (ECRB) and the extensor carpi radialis longus (ECRL), flexor digitorum profundus (FDP), and radius marrow were determined across 7 sections and 4 exercise bouts and a preexercise condition. Results: Significant differences across task and across sections were determined. Post hoc analysis revealed differences in activity between proximal and distal ECRB and ECRL during an exercise and differential activation of the same muscle across the 2 exercise tasks. Bone marrow and FDP did not show task-related changes. The range of average T2 values of bone marrow across sections was greater than a muscle (FDP) that was not the target of the exercise protocol. However, FDP did show small but significant differences across sections. Conclusions: T2-weighted MR images can be used to study muscle activation at 30% and 60% of maximum voluntary contractions. The use of inactive muscle and bone marrow for normalizing data requires further investigation. © 2001 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.

Authors
Livingston, BP; Segal, RL; Song, A; Hopkins, K; English, AW; Manning, CC
MLA Citation
Livingston, BP, Segal, RL, Song, A, Hopkins, K, English, AW, and Manning, CC. "Functional activation of the extensor carpi radialis muscles in humans." Archives of Physical Medicine and Rehabilitation 82.9 (2001): 1164-1170.
PMID
11552185
Source
scival
Published In
Archives of Physical Medicine and Rehabilitation
Volume
82
Issue
9
Publish Date
2001
Start Page
1164
End Page
1170
DOI
10.1053/apmr.2001.24919

fMRI: methodology--acquisition and processing.

Authors
Song, AW; Popp, CA; Mao, J; Dixon, WT
MLA Citation
Song, AW, Popp, CA, Mao, J, and Dixon, WT. "fMRI: methodology--acquisition and processing." Advances in neurology 83 (2000): 177-185.
PMID
10999200
Source
scival
Published In
Advances in neurology
Volume
83
Publish Date
2000
Start Page
177
End Page
185

Segmented spin-echo pulses to increase fMRI signal: repeated intrinsic diffusional enhancement.

Since its inception, functional magnetic resonance imaging (fMRI) has seen rapid progress in the application to neuroscience. Common gradient-recalled acquisition methods are susceptible to static field inhomogeneities, resulting in signal loss at the medial temporal area important for memory function or at the basal ganglia area for motor control. In addition, they are susceptible to the contaminating signals of large vein origin, such as the signals from its surrounding cerebrospinal fluid (CSF) leading to false-positive activation. Spin echoes overcome these drawbacks. However, they are less sensitive to blood oxygenation level dependent (BOLD) susceptibility changes because of their refocusing mechanism. A method is presented here to enhance the spin-echo fMRI signal by recruiting more spins to participate in the dynamic BOLD process. This method divided a conventional T(2) weighting period into several segments separated by blocks of extra free diffusion time. Before the extra diffusion time spins are restored to the longitudinal axis preventing rapid transverse relaxation. This process allows more spin access to the regions that experience the BOLD field gradient. Because of the increased spin population that is modulated by the capillary BOLD field gradient, the functional signal is increased. Spin-echo echo-planar imaging (EPI) with this enhancement may be a useful technique for fMRI studies at inhomogeneous areas such as the air/tissue interface. Magn Reson Med 42:631-635, 1999.

Authors
Song, AW; Mao, H; Muthupillai, R; Haist, F; Dixon, WT
MLA Citation
Song, AW, Mao, H, Muthupillai, R, Haist, F, and Dixon, WT. "Segmented spin-echo pulses to increase fMRI signal: repeated intrinsic diffusional enhancement." Magn Reson Med 42.4 (October 1999): 631-635.
PMID
10502750
Source
pubmed
Published In
Magnetic Resonance in Medicine
Volume
42
Issue
4
Publish Date
1999
Start Page
631
End Page
635

A confrontational naming task produces congruent increases and decreases in PET and fMRI

This work uses the well-established (by PET) confrontation naming task to compare PET and fMRI in a cognitive activation experiment. The signal changes from this task are much less than the changes caused by visual or motor activation tasks used in previous comparisons. ANOVA methods adjusted for multiple comparisons were used to determine significant changes in signal between confrontation naming and figure size discrimination tasks. All 17 significantly increased regions (confrontation naming signal greater) seen on one modality were increased on both modalities. Ten of 13 regions that were significantly decreased on one modality were decreased on the other. Three mismatched regions showed a significant decrease on one modality and a nonsignificant increase on the other. This study could not detect a consistent difference in activation site location between PET and fMRI.

Authors
Votaw, JR; Faber, TL; Popp, CA; Henry, TR; Trudeau, JD; Woodard, JL; Mao, H; Hoffman, JM; Song, AW
MLA Citation
Votaw, JR, Faber, TL, Popp, CA, Henry, TR, Trudeau, JD, Woodard, JL, Mao, H, Hoffman, JM, and Song, AW. "A confrontational naming task produces congruent increases and decreases in PET and fMRI." NeuroImage 10.4 (1999): 347-356.
PMID
10493894
Source
scival
Published In
NeuroImage
Volume
10
Issue
4
Publish Date
1999
Start Page
347
End Page
356
DOI
10.1006/nimg.1999.0471

Continuous functional magnetic resonance imaging reveals dynamic nonlinearities of "dose-response" curves for finger opposition.

Linear experimental designs have dominated the field of functional neuroimaging, but although successful at mapping regions of relative brain activation, the technique assumes that both cognition and brain activation are linear processes. To test these assumptions, we performed a continuous functional magnetic resonance imaging (MRI) experiment of finger opposition. Subjects performed a visually paced bimanual finger-tapping task. The frequency of finger tapping was continuously varied between 1 and 5 Hz, without any rest blocks. After continuous acquisition of fMRI images, the task-related brain regions were identified with independent components analysis (ICA). When the time courses of the task-related components were plotted against tapping frequency, nonlinear "dose- response" curves were obtained for most subjects. Nonlinearities appeared in both the static and dynamic sense, with hysteresis being prominent in several subjects. The ICA decomposition also demonstrated the spatial dynamics with different components active at different times. These results suggest that the brain response to tapping frequency does not scale linearly, and that it is history-dependent even after accounting for the hemodynamic response function. This implies that finger tapping, as measured with fMRI, is a nonstationary process. When analyzed with a conventional general linear model, a strong correlation to tapping frequency was identified, but the spatiotemporal dynamics were not apparent.

Authors
Berns, GS; Song, AW; Mao, H
MLA Citation
Berns, GS, Song, AW, and Mao, H. "Continuous functional magnetic resonance imaging reveals dynamic nonlinearities of "dose-response" curves for finger opposition." The Journal of neuroscience : the official journal of the Society for Neuroscience 19.14 (1999): RC17-.
PMID
10407059
Source
scival
Published In
The Journal of neuroscience : the official journal of the Society for Neuroscience
Volume
19
Issue
14
Publish Date
1999
Start Page
RC17

Plastic changes within the cerebellum associated with motor sequence learning: afMRI study

Authors
Doyon, J; Song, AW; Lalonde, F; Karni, A; Adams, MM; Ungerleider, LG
MLA Citation
Doyon, J, Song, AW, Lalonde, F, Karni, A, Adams, MM, and Ungerleider, LG. "Plastic changes within the cerebellum associated with motor sequence learning: afMRI study." NeuroImage 9.6 PART II (1999): S506-.
Source
scival
Published In
NeuroImage
Volume
9
Issue
6 PART II
Publish Date
1999
Start Page
S506

Segmented spin-echo pulses to increase fMRI signal: Repeated intrinsic diffusional enhancement

Since its inception, functional magnetic resonance imaging (fMRI) has seen rapid progress in the application to neuroscience. Common gradient- recalled acquisition methods are susceptible to static field inhomogeneities, resulting in signal loss at the medial temporal area important for memory function or at the basal ganglia area for motor control. In addition, they are susceptible to the contaminating signals of large vein origin, such as the signals from its surrounding cerebrospinal fluid (CSF) leading to false- positive activation. Spin echoes overcome these drawbacks. However, they are less sensitive to blood oxygenation level dependent (BOLD) susceptibility changes because of their refocusing mechanism. A method is presented here to enhance the spin-echo fMRI signal by recruiting more spins to participate in the dynamic BOLD process. This method divided a conventional T2 weighting period into several segments separated by blocks of extra free diffusion time. Before the extra diffusion time spins are restored to the longitudinal axis preventing rapid transverse relaxation. This process allows more spin access to the regions that experience the BOLD field gradient. Because of the increased spin population that is modulated by the capillary BOLD field gradient, the functional signal is increased. Spin-echo echo-planar imaging (EPI) with this enhancement may be a useful technique for fMRI studies at inhomogeneous areas such as the air/tissue interface.

Authors
Song, AW; Mao, H; Muthupillai, R; Haist, F; Dixon, WT
MLA Citation
Song, AW, Mao, H, Muthupillai, R, Haist, F, and Dixon, WT. "Segmented spin-echo pulses to increase fMRI signal: Repeated intrinsic diffusional enhancement." Magnetic Resonance in Medicine 42.4 (1999): 631-635.
Source
scival
Published In
Magnetic Resonance in Medicine
Volume
42
Issue
4
Publish Date
1999
Start Page
631
End Page
635
DOI
10.1002/(SICI)1522-2594(199910)42:4<631::AID-MRM3>3.0.CO;2-#

Nonlinear spatiotemporal dynamics of functional MRI revealed by independent components analysis

Linear experimental designs have dominated the field of functional neuroimaging, but although successful at mapping regions of relative brain activation, the technique assumes that both cognition and brain activation are linear processes. To test these assumptions, we performed a continuous functional MRI experiment of finger opposition. Subjects performed a visually paced bimanual finger tapping task. The frequency of finger tapping was continuously varied between 1 Hz and 5 Hz, without any rest blocks. After continuous acquisition of fMRI images, the task-related brain regions were identified with Independent Components Analysis (ICA). When the timecourses of the task-related components were plotted against tapping frequency, nonlinear `dose-response' curves were obtained for most subjects. Nonlinearities appeared in both the static and dynamic sense, with hysteresis being prominent in several subjects. The ICA decomposition also demonstrated the spatial dynamics with different components active at different times. These results suggest that the brain response to tapping frequency does not scale linearly, and that it is history dependent even after accounting for the hemodynamic response function. This implies that finger tapping, as measured with fMRI, is a nonstationary process. When analyzed with a conventional General Linear Model, a strong correlation to tapping frequency was identified, but the spatiotemporal dynamics were not apparent.

Authors
Berns, GS; Song, AW; Mao, H
MLA Citation
Berns, GS, Song, AW, and Mao, H. "Nonlinear spatiotemporal dynamics of functional MRI revealed by independent components analysis." Annual International Conference of the IEEE Engineering in Medicine and Biology - Proceedings 2 (1999): 1184--.
Source
scival
Published In
Annual International Conference of the IEEE Engineering in Medicine and Biology - Proceedings
Volume
2
Publish Date
1999
Start Page
1184-

T1-selective diffusion weighted fMRI at 1.5 T

Apparent diffusion coefficients (ADC) of protons contributing to the functional signal can be determined from diffusion weighted functional magnetic resonance imaging (MRI) studies. An earlier study indicated that ADCs calculated from the functional signal of an activated primary sensorimotor cortex are large, and consistent with a CSF or intravascular contribution to the functional signal. We have added inversion recovery pulses to isotropic diffusion weighted imaging to null CSF protons selectively within the imaging slice, or to null the outer volume blood flowing into the imaging slice. With the use of gradient recalled diffusion weighted echo-planar imaging at low gradient b factors, and without the use of inversion pulses, the ADCs×103 in mm2/s (±SD) from the functional signal were 6.81±1.19. These ADCs were significantly higher than resting primary sensorimotor cortex ADCs of 2.26±1.49, measured at the same b factors. When CSF nulling was applied, the functional signal ADCs remained high. Application of inflow nulling decreased the functional signal to such a small value, that ADCs estimated from these functional signals were not assessed. The results are consistent with an intravascular contribution to the functional signal and to its large ADC

Authors
Popp Weingarten, CA; Song, AW; Wong, EC; Cotsonis, G; Hyde, JS
MLA Citation
Popp Weingarten, CA, Song, AW, Wong, EC, Cotsonis, G, and Hyde, JS. "T1-selective diffusion weighted fMRI at 1.5 T." NMR Biomed. (UK) 11.8 (1998): 405-413. (Academic Article)
Source
manual
Published In
NMR Biomed. (UK)
Volume
11
Issue
8
Publish Date
1998
Start Page
405
End Page
413
DOI
10.1002/(SICI)1099-1492(199812)11:83.0.CO;2-8

The use of Repeated Intrinsic Diffuional Enhancement (RIDE) to increase fMRI contrast

Authors
Song, AW; Dixon, WT; Mao, H; Weingarten, CP
MLA Citation
Song, AW, Dixon, WT, Mao, H, and Weingarten, CP. "The use of Repeated Intrinsic Diffuional Enhancement (RIDE) to increase fMRI contrast." NeuroImage 7.4 PART II (1998): S540-.
Source
scival
Published In
NeuroImage
Volume
7
Issue
4 PART II
Publish Date
1998
Start Page
S540

fMRI and PET studies of a visual confrontation naming task

Authors
Popp, CA; Votaw, JR; Faber, TL; Henry, TR; Trudeau, JD; Woodard, J; Mao, H; Woods, RM; Hoffman, JM; Song, AW
MLA Citation
Popp, CA, Votaw, JR, Faber, TL, Henry, TR, Trudeau, JD, Woodard, J, Mao, H, Woods, RM, Hoffman, JM, and Song, AW. "fMRI and PET studies of a visual confrontation naming task." NeuroImage 7.4 PART II (1998): S148-.
Source
scival
Published In
NeuroImage
Volume
7
Issue
4 PART II
Publish Date
1998
Start Page
S148

Clinical application of fMRI: Motor cortex activation in a paralysed patient

Authors
Mao, H; Muthupillai, R; Kennedy, PR; Popp, CA; Song, AW
MLA Citation
Mao, H, Muthupillai, R, Kennedy, PR, Popp, CA, and Song, AW. "Clinical application of fMRI: Motor cortex activation in a paralysed patient." MedicaMundi 42.3 (1998): 19-22.
Source
scival
Published In
MedicaMundi
Volume
42
Issue
3
Publish Date
1998
Start Page
19
End Page
22

The effect of off-resonance radiofrequency pulse saturation on fMRI contrast

This paper describes the use of off-resonance saturation to further manipulate the blood oxygenation level dependent (BOLD) contrast of fMRI. A customized narrow bandwidth radiofrequency pulse, applied with a range of frequency offsets prior to selection of each slice, was designed and incorporated into a gradient echo EPI sequence. This application takes advantage of the resonance frequency and linewidth differences between the oxygenated and deoxygenated state of blood in human brain during task activation and rest, and is capable of creating an enhancement in the contrast of the BOLD effect. Because of a possible contribution to the signal change from cerebro-spinal fluid, which has a much narrower linewidth and smaller frequency shift compared with the brain tissue, data were also collected using a nulling inversion pulse The inversion pulse was applied before the off-resonance pulse and data acquisition to eliminate the CSF signal. Functional areas are thus more localized to the brain tissue.

Authors
Song, AW; Wolff, SD; Balaban, RS; Jezzard, P
MLA Citation
Song, AW, Wolff, SD, Balaban, RS, and Jezzard, P. "The effect of off-resonance radiofrequency pulse saturation on fMRI contrast." NMR in Biomedicine 10.4-5 (1997): 208-215.
PMID
9430350
Source
scival
Published In
Nmr in Biomedicine
Volume
10
Issue
4-5
Publish Date
1997
Start Page
208
End Page
215

Dynamic changes in the motor cortical areas, striatum and cerebellum during explicit and implicit learning of a visuomotor skill: A fMRI study

Authors
Doyon, J; Karni, A; Song, AW; Adams, MM; Maisog, JM; Ungerleider, LG
MLA Citation
Doyon, J, Karni, A, Song, AW, Adams, MM, Maisog, JM, and Ungerleider, LG. "Dynamic changes in the motor cortical areas, striatum and cerebellum during explicit and implicit learning of a visuomotor skill: A fMRI study." NeuroImage 5.4 PART II (1997): S601-.
Source
scival
Published In
NeuroImage
Volume
5
Issue
4 PART II
Publish Date
1997
Start Page
S601

Diffusion weighted fMRI at 1.5 T

Functional magnetic resonance imaging (fMRI) is capable of detecting task- induced blood oxygenation changes using susceptibility sensitive pulse sequences such as gradient-recalled echo-planar imaging (EPI). The local signal increases seen in the time course are believed to be due to an increase in oxygen delivery that is incommensurate with oxygen demands. To help isolate the sources of functional signal changes, the authors have incorporated various forms of diffusion weighting into EPI pulse sequences to characterize the apparent mobility of the functionally modulated protons. Results suggest that the majority of the functional signal at 1.5 T arises from protons that have apparent diffusion coefficients that are approximately four or five times higher than that of brain tissue. This implies that significant functional signal sources are either protons within the vascular space or protons from the perivascular space that is occupied by cerebrospinal fluid.

Authors
Song, AW; Wong, EC; Tan, SG; Hyde, JS
MLA Citation
Song, AW, Wong, EC, Tan, SG, and Hyde, JS. "Diffusion weighted fMRI at 1.5 T." Magnetic Resonance in Medicine 35.2 (1996): 155-158.
PMID
8622577
Source
scival
Published In
Magnetic Resonance in Medicine
Volume
35
Issue
2
Publish Date
1996
Start Page
155
End Page
158
DOI
10.1002/mrm.1910350204

Technical foundations and pitfalls of clinical fMRI

Magnetic resonance imaging (MRI) has become an established and invaluable tool in the diagnosis of numerous diseases through its ability to show pathologic contrast in images of soft tissue. More recently, MRI has found application in the study of organ function, principally in the brain and heart. This article deals with MRI imaging of brain function and describes some of the techniques that allow physiological parameters such as cerebral blood volume, cerebral blood oxygenation, and cerebral perfusion to be determined. Additionally, some of the potentially confounding influences in these experiments are discussed.

Authors
Jezzard, P; Song, AW
MLA Citation
Jezzard, P, and Song, AW. "Technical foundations and pitfalls of clinical fMRI." NeuroImage 4.3 SUPPL. 2 (1996): S63-S75.
PMID
9345530
Source
scival
Published In
NeuroImage
Volume
4
Issue
3 SUPPL. 2
Publish Date
1996
Start Page
S63
End Page
S75
DOI
10.1006/nimg.1996.0056

Optimized isotropic diffusion weighting

The authors introduce several sets of time-efficient gradient waveforms for applying isotropic diffusion weighting in NMR experiments. This creates signal attenuation that depends on the trace of the diffusion tensor and is therefore rotationally invariant. Numerical methods for the calculation of such gradient sets are outlined, and results are shown for isotropic and anisotropic gradient hardware and first order flow moment hulled diffusion weighting gradients. Preliminary experimental results from the human brain validate this new technique.

Authors
Wong, EC; Cox, RW; Song, AW
MLA Citation
Wong, EC, Cox, RW, and Song, AW. "Optimized isotropic diffusion weighting." Magnetic Resonance in Medicine 34.2 (1995): 139-143.
PMID
7476070
Source
scival
Published In
Magnetic Resonance in Medicine
Volume
34
Issue
2
Publish Date
1995
Start Page
139
End Page
143
DOI
10.1002/mrm.1910340202

Echo-volume imaging

Two single-shot volume imaging techniques are described. The first, single-echo echo-volume imaging, is essentially the echo-volume imaging (EVI) sequence suggested by Mansfield (J. Phys. C. 10, L55 (1977)). The second is a multi-spin-echo approach in which one plane of k-space is collected during each spin echo. In both techniques, phase encoding gradients are applied in the z direction, and three-dimensional k-space is filled by a raster pattern in Cartesian coordinates. Spatial saturation is used to avoid aliasing in the y direction, and a selective pulse is applied to excite the desired slab of tissue and eliminate aliasing in z. The average echo-times, measured from the center of the 90° pulse to the center of the acquisition k-space (k(x) = k(y) = k(z) = 0), were 45 and 104 ms for single echo and multi-echo methods, respectively. Images of the human brain using both sequences are shown.

Authors
Song, AW; Wong, EC; Hyde, JS
MLA Citation
Song, AW, Wong, EC, and Hyde, JS. "Echo-volume imaging." Magnetic Resonance in Medicine 32.5 (1994): 668-671.
PMID
7808270
Source
scival
Published In
Magnetic Resonance in Medicine
Volume
32
Issue
5
Publish Date
1994
Start Page
668
End Page
671
DOI
10.1002/mrm.1910320518
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