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Recent Publications

 
 

Functional MRI in the investigation of blast-related traumatic brain injury


Published: 3/4/2013

Authors:

John Graner(1,2), Terrence R. Oakes(1,2), Louis M. French(3,4,5) and Gerard Riedy(1,2)

Key :
1 National Intrepid Center of Excellence,Walter Reed National Military Medical Center, Bethesda, MD, USA
2 National Capital Neuroimaging Consortium, Uniformed Servies University of the Health Sciences, Bethesda, MD, USA
3 Walter Reed National Military Medical Center, Bethesda, MD, USA
4 Center for Neuroscience and Regenerative Medicine, Bethesda, MD, USA
5 Defense and Veterans Brain Injury Center,Walter Reed National Military Medical Center, Bethesda, MD, USA


Abstract:
This review focuses on the application of functional magnetic resonance imaging (fMRI) to the investigation of blast-related traumatic brain injury (bTBI). Relatively little is known about the exact mechanisms of neurophysiological injury and pathological and functional sequelae of bTBI. Furthermore, in mild bTBI, standard anatomical imaging techniques (MRI and computed tomography) generally fail to show focal lesions and most of the symptoms present as subjective clinical functional deficits. Therefore, an objective test of brain functionality has great potential to aid in patient diagnosis and provide a sensitive measurement to monitor disease progression and treatment. The goal of this review is to highlight the relevant body of blast-related TBI literature and present suggestions and considerations in the development of fMRI studies for the investigation of bTBI. The review begins with a summary of recent bTBI publications followed by discussions of various elements of blastrelated injury. Brief reviews of some fMRI techniques that focus on mental processes commonly disrupted by bTBI, including working memory, selective attention, and emotional processing, are presented in addition to a short reviewof resting state fMRI. Potential strengths and weaknesses of these approaches as regards bTBI are discussed. Finally, this review presents considerations that must be made when designing fMRI studies for bTBI populations, given the heterogeneous nature of bTBI and its high rate of comorbidity with other physical and psychological injuries.
Keywords: blast injuries, traumatic brain injury, review, military injury, functional magnetic resonance imaging




 
 

Uncovering latent deficits due to mild traumatic brain injury by using normobaric hypoxia stress


Published: 4/1/2013

Authors:

Leonard Temme(1), Joseph Bleiberg(2), Dennis Reeves(3), David L. Still(1), Dan Levinson(4) and Rebecca Browning(3)

Key :
1 Vision Sciences Branch, Sensory Research Division, U.S. Army Aeromedical Research Laboratory, Fort Rucker, AL, USA
2 National Intrepid Center of Excellence,Walter Reed National Military Medical Center, Bethesda, MD, USA
3 Clinvest Research, Springfield, MO, USA
4 California School of Forensic Studies, Alliant International University Irvine, Irvine, CA, USA


Abstract:
Memory deficits and other cognitive symptoms frequently associated with mTBI are commonly thought to resolve within 7–10 days. This generalization is based principally on observations made in individuals who are in the unstressed environmental conditions typical to a clinic and so does not consider the impact of physiologic, environmental, or psychological stress. Normobaric hypoxic stress can be generated with normal mean sea level (MSL) air, which is about 21% oxygen (O2) and 78% nitrogen (N), by reducing the percentage of O2 and increasing the percentage of N so that the resultant mixed-gas has a partial pressure of O2 approximating that of specified altitudes.This technique was used to generate normobaric hypoxic equivalents of 8,000, 12,000, and 14,000 feet above MSL in a group of 36 volunteers with a mTBI history and an equal number of controls matched on the basis of age, gender, tobacco smoking consumption, weight, height, and body mass index. Short-term visual memory was tested using the Matching to Sample (M2S) subtest of the BrainCheckers analog of the Automated Neuropsychological Assessment Metrics. Although there were no significant differences in M2S performance between the two groups of subjects at MSL, with increased altitude, the mTBI group performance was significantly worse than that of the control group. When the subjects were returned to MSL, the difference disappeared. This finding suggests that the “hypoxic challenge” paradigm developed here has potential clinical utility for assessing the effects of mTBI in individuals who appear asymptomatic under normal conditions.
Keywords: mild traumatic brain injury, normobaric hypoxia, cognitive stress test, concussion, BrainCheckers, automated neuropsychological assessment metrics, mTBI biomarkers, hypoxic challenge




 
 

Diffusion Tensor Imaging and Its Application to Traumatic Brain Injury: Basic Principles and Recent Advances


Published: 12/1/2012

Authors:

Ping-Hong Yeh(1), Terrence R. Oakes(2,3), Gerard Riedy(1,2,3,4)

Key :
1 Traumatic Brain Injury Image Analysis Lab, Henry Jackson Foundation for the Advancement of Military Medicine, Rockville, USA
2 National Intrepid Center of Excellence, Bethesda, USA
3 National Capital Neuroimaging Consortium, Walter Reed National Military Medical Center, Bethesda, USA
4 Center for Neuroscience and Regenerative Medicine, Uniformed Services University of the Health Sciences, Bethesda, USA Email: *pinghongyeh@gmail.com


Abstract:
Traumatic axonal injury is a progressive process evoked by shear forces on the brain, gradually evolving from focal axonal alteration and cumulating in neural disconnection. Clinical classifiers and conventional neuroimaging are limited in traumatic axonal injury detection, outcome prediction, and treatment guidance. Diffusion weighted imaging is an advanced magnetic resonance imaging (MRI) technique that is sensitive to the movement of water molecules, providing additional information on the micro-structural arrangement of tissue. Quantitative analysis of diffusion metrics can aid in the localization of axonal injury and/or de(dys)myelination caused by trauma. Diffusion MRI tractography is an ex-tension of diffusion weighted imaging, and can provide additional information about white matter pathways and the integrity of brain neural networks. Both techniques are able to detect the early micro-structural changes caused by Traumatic Brain Injury (TBI), and can be used to increase understanding of the mechanisms of brain plasticity in re-covery after brain injury and possibly optimize treatment planning of patients with Traumatic Brain Injury. This review focuses on the theoretical basis and applied advanced techniques of diffusion weighted imaging, their limitations and applications, and future directions in the application to TBI.
Keywords: Brain Network; Connectivity; High Angular Resolution Diffusion Imaging (HARDI); Diffusion Tensor Imaging (DTI); Neurocircuitry; Neuroimaging; Traumatic Axonal Injury (TAI); Traumatic Brain Injury (TBI); Tractography; White Matter




 
 

Perfusion deficits in patients with mild traumatic brain injury characterized by dynamic susceptibility contrast MRI


Published: 11/30/2012

Authors:

Wei Liu(a,b), Binquan Wang(a,b), Rachel Wolfowitz(a,b,c), Ping-Hong Yeh(a,b), Dominic E. Nathan(a,b), John Graner(a,c), Haiying Tangd, Hai Pan(a,b), Jamie Harper(a,c), Dzung Phame, Terrence R. Oakes(a,c), Louis M. French(d,e,f) and Gerard Riedy(a,c*)

Key :
* Correspondence to: G. Riedy, National Intrepid Center of Excellence, Bethesda, MD, USA, 20889. E-mail: Gerard.riedy@med.navy.mil
a W. Liu, B. Wang, R. Wolfowitz, P.-H. Yeh, D. E. Nathan, J. Graner, H. Pan,
J. Harper, T.R. Oakes, G. Riedy
National Capital Neuroimaging Consortium (NCNC), Bethesda, MD, USA
b W. Liu, B. Wang, R. Wolfowitz, P.-H. Yeh, D. E. Nathan, H. Pan
Henry M. Jackson Foundation for the Advancement of Military
Medicine, Bethesda, MD, USA
c R. Wolfowitz, J. Graner, J. Harper, T. R. Oakes, G. Riedy National Intrepid Center of Excellence (NICoE), Bethesda, MD, USA
d H. Tang, L. M. French
Uniformed Services University of the Health Sciences (USUHS), Bethesda, MD, USA
e D. Pham, L. M. French
Center for Neuroscience
f L. M. French
Walter Reed National Military Medical Center (WRNMMC), Bethesda, MD, USA


Abstract:
Perfusion deficits in patients with mild traumatic brain injury (TBI) from a military population were characterized by dynamic susceptibility contrast perfusion imaging. Relative cerebral blood flow (rCBF) was calculated by amodel-independent deconvolution approach from the tracer concentration curves following a bolus injection of gadolinium diethylenetriaminepentaacetate (Gd-DTPA) using both manually and automatically selected arterial input functions (AIFs). Linear regression analysis of themean values of rCBF from selected regions of interest showed a very good agreement between the two approaches, with a regression coefficient of R=0.88 and a slope of 0.88. The Bland–Altman plot also illustrated the good agreement between the two approaches, with a mean difference of 0.612.4mL/100g/min. Voxelwise analysis of rCBF maps from both approaches demonstrated multiple clusters of decreased perfusion (p<0.01) in the cerebellum, cuneus, cingulate and temporal gyrus in the group with mild TBI relative to the controls.MRI perfusion deficits in the cerebellum and anterior cingulate also correlated (p<0.01) with neurocognitive results, including the mean reaction time in the Automated Neuropsychological Assessment Metrics and commission error and detection T-scores in the Continuous Performance Test, as well as neurobehavioral scores in the Post-traumatic Stress Disorder Checklist–Civilian Version. In conclusion, rCBF calculated using AIFs selected from an automated approach demonstrated a good agreement with the corresponding results using manually selected AIFs. Group analysis of patients with mild TBI froma military population demonstrated scattered perfusion deficits, which showed significant correlations withmeasures of verbalmemory, speed of reaction time and self-report of stress symptoms. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Keywords: dynamic susceptibility-weighted MRI; perfusion; arterial input function; relative cerebral flood flow; traumatic brain injury