 This study is being done to learn about inflammation and amyloid in Alzheimers disease. A type of brain scan called a PET scan is used measure 1 inflammation and 2 abnormal accumulation of a the amount of a certain protein fragment called beta-amyloid plaques in the brain. These are thought to be involved in Alzheimers disease. The investigators will also perform brain MRI and do tests to measure the participants memory and thinking. 