PET Imaging in Chronic Traumatic Encephalopathy

Background: \- Chronic traumatic encephalopathy (CTE) is a brain disease caused in part by head injury. The brain changes from CTE can only be seen at autopsy. Researchers want to test a new brain scan to help diagnose CTE in living patients. Objective: \- To determine if a new type of brain scan can detect changes that occur in chronic traumatic encephalopathy. Eligibility: \- Adults age 18 60 with previous head injury or participation in certain sports. Design: * Participants will be screened with: * Physical exam * Blood and urine tests * Tests of thinking, mood, and memory * 30-minute magnetic resonance imaging (MRI) brain scan. A magnetic field and radio waves take pictures of the brain. Participants will lie on a table that slides into a metal cylinder. They will get earplugs for the loud knocking sounds. * Visit 1: Participants will have a 70-minute PET scan of the brain with a small amount of a radioactive chemical. That will be injected through an intravenous tube (catheter) in each arm. A catheter will also be put into an artery at the wrist or elbow. * Participants will lie on a bed that slides in and out of a donut-shaped scanner. A plastic mask may be molded to their face and head. Vital signs and heart activity will be checked before and during the scan. * Blood and urine will be taken before and after the scan. * Participants will be checked on by phone the next day. * Visit 2: Participants will repeat Visit 1 with a different chemical and no artery catheter. * Visit 3: Participants may have a spinal tap. Some fluid will be removed by needle between the bones in the back.