Risk Prediction for Alzheimer Dementia With Brain Imaging and Genetics

The purpose of this study is to learn about how trauma, posttraumatic stress disorder (PTSD), and mild traumatic brain injury that can occur during deployment affect the brain. The investigators also want to learn how PTSD and mild traumatic brain injury can affect the chance of developing Alzheimer disease later in life. The investigators will study this by using magnetic resonance imaging and positron emission tomography scans to obtain pictures of the brain.