Observational Study of Cognitive Outcomes for Subjects Who Have Had Prior PET Amyloid Imaging With Florbetapir F 18 (18F-AV-45)

The primary objective of this protocol is to determine if brain amyloid imaged with florbetapir F 18 (18F-AV-45) PET scans is predictive of progressive cognitive impairment during the subsequent 36 months for groups of: normal controls, mild cognitive impairment and Alzheimer's disease. Hypothesis 1: The probability a subject will experience progressive cognitive impairment within 36 months of imaging will be greater in subjects whose 18F-AV-45 PET scan was rated amyloid positive compared to subjects whose PET scan was rated amyloid negative. The secondary objective is to determine the stability, over 36 months of a clinical diagnosis, of AD in patients with an amyloid positive 18F-AV-45 PET. Hypothesis 2: The diagnosis of AD will remain unchanged in patients whose PET scan were rated as amyloid positive.