MULTIMODAL NEUROIMAGING IN BLAST INDUCED TRAUMATIC BRAIN INJURY

Recent military conflicts in Iraq and Afghanistan have resulted in an increase in the number of blast related traumatic brain injury (TBI) cases, currently estimated in excess of 300,000. Current neuroimaging methods, including MRI and CT, are generally not sensitive enough to diagnose blast TBL This research represents several advancements in the understanding of long-term TBI related changes as well as imaging comorbid neurocognitive deficits and psychopathologies. The multi modal approach was taken to leverage the differing sensitivities of each imagmg modality to better identify neuroimaging changes associated with blast TBL T l-weighted MRI was utilized to assess cortical thickness reduction in the TBI subjects, resulting in right temporal lobe decreases that were associated with posttraumatic stress disorder (PTSD) and neurobehavioral symptom indices. Utilizing positron emission tomography (PET), several areas of metabolic change were associated with blast TBI, PTSD, repetitive head injury, and TBI severity. Functional MRI was used to assess working memory deficit, demonstrating relatively normal function in the mild TBI subject, except for at higher cognitive loads; whereas the moderate TBI subjects demonstrated a trend of dysfunction at most levels of cognitive load. Fractional anisotropy (FA) changes were assessed using diffusion tensor imaging, however there was no resulting statistical significance due to differences in the locations of single subject FA changes that could not be realized at the group level using standard analyses. Investigation into multimodal searchlight to integrate the sensitivities of each imaging modality into a single statistical measure, provided enhanced sensitivity to TBI-induced changes in neuroimaging versus single modal searchlight and identified several clusters of change most notably in the cerebellum, temporal lobes, brainstem, and internal capsule. Through a multimodal approach we have shown several areas of damage and dysfunction associated with blast TBI in subjects greater than one year post injury. This research is important due to the large numbers of subjects currently experiencing long-term post concussive symptoms. Our findings show that both TBI and PTSD playa large role in the changes identified on neuroimaging. This research can provide information to assist in the understanding , diagnosis , and treatment of blast TBI.Ph.D. in Biomedical Engineering, December 201