Neuroinflammation Imaging in AD

This research study is being done to learn more about inflammation in the brain using Positron Emission Tomography/Computed Tomography (PET/CT) imaging in people with Alzheimer's Disease/Mild Cognitive Impairment or healthy controls. If the subject agrees to be in this study, she/ he will have a PET/CT scan using the investigational radiotracer \[18F\]NOS. A subject with a specific genetic polymorphism may also agree to be in the sub-study in which she/he will have another PET/CT scan using the investigational tracer \[11C\]PBR28 for comparison with the FNOS \[18F\]NOS scan. For subjects who agree to this sub-study they may undergo the brain PET/CT scan with \[11C\]PBR28 either on the same day as the \[18F\]NOS PET/CT or on another day. The subject may have a screening visit before the PET/CT scan visit if the investigator needs to confirm the subject is able to be in the study. A blood sample will be taken before the scans. Additional blood samples will be taken during the PET scans. Subjects must also agree to have an MRI scan for this research study if she/he has not had a recent scan that the study doctor decides can be used for this study.