We have identified a positron-emitting imaging agent that is specific for the colony stimulating factor receptor 1 (CSF1R), which is expressed on activated microglia. Our hypothesis is that activated microglia underlie the inflammatory component of Alzheimer's disease (AD) and accordingly provide some of the earliest changes seen in the brains of patients with AD. We use a highly sensitive brain imaging technique called positron emission tomography (PET) that will enable us to visualize and measure the degree of microglial activation in the brains of patients with AD in comparison to healthy, age-matched, cognitively normal controls. We have two goals in this project: (1) to validate our initial PET imaging agent as an early, noninvasive biomarker in patients with AD; and, (2) develop a second PET agent that is radiolabeled with an isotope that is more amenable to clinical translation and widespread, multi-center dissemination. Our ultimate goal with that second agent is a commercial PET imaging biomarker for AD.