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Veterans of recent military conflicts have experienced a high rate of mild traumatic brain injuries from exposure to blasts (bTBI). Difficulty detecting the neuroanatomical effects of bTBI using standard imaging protocols, including diffusion tensor imaging (DTI), has hindered the development of evidence-based treatments. A possible reason for this challenge is that many past DTI studies attempting to identify neuroanatomical markers of bTBI have ignored the broad range of cumulative blast exposure among Veterans, and therefore potentially reduced sensitivity to associations between bTBI and DTI metrics. Here, we compare commonly used DTI metrics: fractional anisotropy and mean, axial, and radial diffusivity (FA, MD, AD, RD) in U.S. Military Veterans with and without a history of blast exposure using both the traditional method of dividing participants into two equally weighted groups, and an alternative method, wherein each participant is weighted by their blast exposure quantity, severity, and recency. While no differences in FA, MD, and AD (and minimal in RD) were detected using the traditional method, the alternative method revealed diffuse and extensive changes in all four DTI metrics associated with bTBI. These effects were quantified within 80 anatomically-defined white matter tracts as the percentage of voxels with significant changes, which identified the acoustic and optic radiations, fornix, uncinate fasciculus, inferior occipito-frontal fasciculus, cingulum, and the anterior commissure as the pathways most affected by bTBI. Moreover, additive effects of aging were present in many of the same tracts suggesting that the neuroanatomical effects of bTBI may compound with age. |
