Brain Uptake and Safety With Probable Alzheimer's Disease, Amnestic Mild Cognitive Impairment and Healthy Volunteers

Inclusion Criteria: * The subject meets National Institute of Neurological and Communicative Disorders and Stroke; Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) criteria for clinically probable AD and Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV) criteria for dementia of Alzheimer's type. * The subject meets Petersen criteria for amnestic MCI. * The subject has no evidence of cognitive impairment by medical history. Exclusion Criteria: * The subject may not be able to complete the study as judged by the investigator. * The subject has received ionising radiation exposure from clinical trials in the last 12 months or has participated in any other clinical study within 30 days of study entry. * The subject has known allergies to \[18F\]AH110690 or \[11C\]PIB or their constituents. * The subject is pregnant or breast-feeding. * The subject has a history of alcohol and/or drug abuse within the last 2 years based upon a review of medical records. * The subject has a contraindication for MRI (including, but not limited to, claustrophobia, pacemaker, presence of metallic fragments near the eyes or spinal cord, or cochlear implant). * The subject has a history of head injury with loss of consciousness.