18F-AV-1451 and Florbetapir F 18 PET (Positron Emission Tomography) Imaging in Subjects at Risk for Chronic Traumatic Encephalopathy

Inclusion Criteria: * Male subjects consented and currently enrolled in the Diagnosing and Evaluating Traumatic Encephalopathy Using Clinical Tests (DETECT) or the Long-Term Consequences of Repetitive Brain Injury in Athletes study protocols * Can tolerate up to two PET imaging sessions * Have the ability to provide informed consent for study procedures Exclusion Criteria: * Claustrophobia * Current clinically significant cardiovascular disease or clinically significant abnormalities on screening ECG * History of risk factors for Torsades de Pointes or are taking drugs known to cause QT-prolongation * Current clinically significant infectious disease, endocrine or metabolic disease, pulmonary, renal or hepatic impairment, or cancer that the investigator believes would affect study participation or scan results * Have had a non-study related radiopharmaceutical imaging or treatment within 7 days prior to study PET imaging sessions