Imaging Characteristics of a Follow-up 18F-AV-1451 Scan

Inclusion Criteria: * Have a previous 18F-AV-1451 brain scan * Can tolerate up to two Positron Emission Tomography (PET) imaging sessions and a Magnetic Resonance Imaging (MRI) scan * Ability to provide informed consent Exclusion Criteria: * Current clinically significant psychiatric disease * Are claustrophobic * Current clinically significant cardiovascular disease or ECG abnormalities, or additional risk factors for Torsades de Pointes * Current clinically significant infectious disease, endocrine or metabolic disease, pulmonary, renal or hepatic impairment, or cancer * Females of childbearing potential who are not surgically sterile, not refraining from sexual activity or not using reliable methods of contraception * Have had a non-study related radiopharmaceutical imaging or treatment procedure within 7 days prior to the study imaging session