<qa>  What is the target number of completers?This study is being done to determine the relationship between inflammation, cognitive impairment, and amyloid burden in elderly subjects with different clinical and biomarker profiles of Alzheimers disease AD. Participants will undergo amyloid PET imaging with 18F-Florbetaben with target number of completers being 15 amyloid-positive elders with impairment, 15 amyloid-positive elders with normal cognition, 15 amyloid-negative elders with impairment, and 15 amyloid-negative elders with normal cognition. Subjects will undergo screen that includes neuropsychological testing, brain MRI, and PET imaging with 18F-florbetaben to define the above 4 groups. Subjects will have 11C-PBR28 PET imaging to measure the 18 kDa translocator protein a marker of inflammation. Subjects will have the option to have lumbar puncture performed to measure CSF concentrations of amyloid,tau, phospho-tau, and inflammatory markers. 