Ability Of ([18F]-AV-45) PET Scan to Distinguish Alzheimer's Disease Subjects From Cognitively Normal Individuals

This study will evaluate the performance characteristics of a novel \[18F\] amyloid detection ligand (18F\]-AV-45) with respect to its ability to distinguish patients with clinically-diagnosed probable Alzheimer's disease from cognitively normal elderly subjects and to independently compare its diagnostic performance characteristics with the ability of \[11C\]PIB to correctly categorize the same subjects. SPECIFIC HYPOTHESES 1. Individuals with a clinical diagnosis of probable Alzheimer's disease will have increased brain retention of \[18F\]-AV-45 compared to cognitively normal elderly individuals. 2. There will be no clinically meaningful difference in the amyloid retention performance characteristics of \[18F\]-AV-45 and \[l1C\]PIB.