In addition to the above hypotheses, neuropathological data from autopsy follow-up will be used to determine correlations between regional plaque and tangle deposition patterns and PET signals. Investigators will create PET cortical surface maps for [F-18]FDDNP-PET between subjects with Traumatic Brain Injury and controls compared with region of interest analysis in transaxial PET images. MRI scans will be available for diffusion tensor imaging (DTI), and investigators will use these DTI measures to confirm our anticipated findings of greater white matter integrity in controls compared with AD patients.