Soldiers from the US Army, with well characterized diagnosis of mTBI or PTSD, will be recruited in the first year as will age-matched healthy controls from the military and civilian populations. MRI, single voxel MRS, and two-dimensional correlated spectroscopy (2D COSY) MRS will be acquired from each participant at the Brigham and Women's Hospital (BWH). This data will be anonymized and transferred to the Draper Laboratories. Biomarkers for each disease will be identified by comparison with control data. These biomarkers will then be fed into classifiers that will then be validated with a similar cohort acquired in the second year. The second cohort of subjects will then be incorporated into the classifier algorithms for a stronger and more robust classification from which a diagnostic test will emerge. To test this diagnostic evaluation the data analysis by both BWH and Draper labs will be blinded to the characterization of the participants and from the MRS results, the investigators will predict if the participant has mTBI, PTSD, both, or neither. Finally, all data will then be fused into the algorithms to provide a final classifier. The results of the final classifier will then be correlated with clinical, neuropsychological, and neuroanatomical indices of mTBI and PTSD. These correlations will provide the most complete biochemical analysis of mTBI and PTSD which may lead to insight into alternate pathways for drug development.