Although the exact number of affected individuals is unknown, it has been estimated that approximately 20% of U.S. veterans of Operations Enduring Freedom (OEF) and Iraqi Freedom (OIF) have experienced mild traumatic brain injury (mTBI) (i.e., concussion), which is defined as a brief loss or alteration of consciousness from a blow or jolt to the head. Blast exposure is among the most common causes of concussion in OEF-OIF warriors. Although the mechanism is unknown, major depressive disorder (MDD) after head injury is common. The purpose of this study was to use diffusion tensor imaging (DTI) and functional magnetic resonance imaging (fMRI) to examine the structural and functional neural correlates of MDD in OEF-OIF combat veterans with a self-reported history of blast-related concussion. We hypothesized that subjects in the MDD group (i.e., individuals with a history of blast-related concussion who were experiencing current MDD) relative to individuals in the non-MDD group (i.e., individuals with a history of blast-related concussion but no current or lifetime history of MDD) would show amygdala hyperactivity and disruption of white matter tracts connecting prefrontal and limbic brain regions. To test these hypotheses, 11 MDD and 11 non-MDD individuals underwent DTI and performed a validated emotional face matching task during fMRI. MDD relative to non-MDD individuals showed greater activity during fear matching trials in the amygdala and other emotion processing structures, lower activity during fear matching trials in emotional control structures such as the dorsolateral prefrontal cortex and lower fractional anisotropy (FA) in several white matter tracts including the superior longitudinal fasciculus (SLF). Greater depressive symptom severity correlated negatively with FA in the SLF. These results suggest a biological basis of MDD in OEF-OIF veterans who have experienced blast-related concussion, and may contribute to the development of treatments aimed at improving the clinical care of this unique population of wounded warriors.
[Show abstract][Hide abstract] ABSTRACT: Traumatic brain injury (TBI) remains one of the most prevalent forms of morbidity among Veterans and Service Members, particularly for those engaged in the conflicts in Iraq and Afghanistan. Neuroimaging has been considered a potentially useful diagnostic and prognostic tool across the spectrum of TBI generally, but may have particular importance in military populations where the diagnosis of mild TBI is particularly challenging, given the frequent lack of documentation on the nature of the injuries and mixed etiologies, and highly comorbid with other disorders such as post-traumatic stress disorder, depression, and substance misuse. Imaging has also been employed in attempts to understand better the potential late effects of trauma and to evaluate the effects of promising therapeutic interventions. This review surveys the use of structural and functional neuroimaging techniques utilized in military studies published to date, including the utilization of quantitative fluid attenuated inversion recovery (FLAIR), susceptibility weighted imaging (SWI), volumetric analysis, diffusion tensor imaging (DTI), magnetization transfer imaging (MTI), positron emission tomography (PET), magnetoencephalography (MEG), task-based and resting state functional MRI (fMRI), arterial spin labeling (ASL), and magnetic resonance spectroscopy (MRS). The importance of quality assurance testing in current and future research is also highlighted. Current challenges and limitations of each technique are outlined, and future directions are discussed.
Brain Imaging and Behavior 09/2015; DOI:10.1007/s11682-015-9444-y · 4.60 Impact Factor
"Recent advances and the emergence of newer functional imaging techniques such as Diffusion Tensor Imaging (DTI), fl uorodeoxyglucose positron emission tomography (FDG-PET), Single Photon Emission Computed Tomography (SPECT) and functional Magnetic Resonance Imaging (fMRI) have shown great potential in detecting brain tissue damage that are invisible in CT and MRI. These newer technologies therefore, may have a signifi cant potential in diagnosing mTBI in future (Brenner, 2011; Matthews et al., 2011). The availability of these imaging tools, however, is very limited and will require further experimental validation and correlation with the neurophysiological paradigms of TBI. "
"Various modalities of magnetic resonance
imaging (MRI), including diffusion tensor imaging (DTI), have been utilized in clinical
settings following TBI78910. However, only a limited number of clinical
studies included readouts at several post-injury time points in Veterans11121314151617. DTI's sensitivity relative to conventional imaging
tools has prompted its recent use in experimental mTBI181920 with a few
rodent blast-induced TBI (bTBI) studies21222324. "
[Show abstract][Hide abstract] ABSTRACT: Mild blast-induced traumatic brain injury (mbTBI) poses special diagnostic challenges due to its overlapping symptomatology with other neuropsychiatric conditions and the lack of objective outcome measures. Diffusion tensor imaging (DTI) can potentially provide clinically relevant information toward a differential diagnosis. In this study, we aimed to determine if single and repeated (5 total; administered on consecutive days) mild blast overpressure exposure results in detectable structural changes in the brain, especially in the hippocampus. Fixed rat brains were analyzed by ex vivo DTI at 2 h and 42 days after blast (or sham) exposure(s). An anatomy-based region of interest analysis revealed significant interactions in axial and radial diffusivity in a number of subcortical structures at 2 h only. Differences between single- and multiple-injured rats were largely in the thalamus but not the hippocampus. Our findings demonstrate the value and the limitations of DTI in providing a better understanding of mbTBI pathobiology.
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