Clinical Evaluation of Flortaucipir F 18

Subjects should meet inclusion and exclusion criteria for the companion protocol in addition to the criteria below. Inclusion Criteria: * Subjects who have a historical volumetric magnetic resonance imaging (MRI) as part of the companion study Exclusion Criteria: * Have clinically significant cardiac, hepatic, renal, pulmonary, metabolic, or endocrine disturbances * Have a screening electrocardiogram with a corrected QT interval (QTc) \> 450 msec if male or QTc \> 470 msec if female * Have a history of additional risk factors for Torsades de Pointes (TdP) or are taking drugs known to cause QT-prolongation. Patients with a prolonged QTc interval in the setting of intraventricular conduction block may be enrolled with sponsor approval * Have a history of drug or alcohol dependence within the last year, or prior prolonged history of dependence unless approved by the sponsor * Are females of childbearing potential who are not surgically sterile, not refraining from sexual activity or not using reliable methods of contraception * Have a history of relevant severe drug allergy or hypersensitivity * Are patients who have received an investigational medication within 30 days prior to the planned imaging session for this study * Are patients with current clinically significant unstable medical comorbidities * Are patients who have received a radiopharmaceutical for imaging or therapy within the past 24 hours prior to the imaging session for this study