The aim of the study is to determine if regional cerebral blood flow, measured by dynamic arterial spin labeling (dASL), can be a biomarker for stage of Alzheimer's disease. The study is designed to be conducted in 2 parts in participants with mild to moderate Alzheimer's disease, and participants with normal cognition. Various imaging studies will be done using magnetic resonance imaging (MRI) and positron emission tomography (PET) along with neurocognitive assessments. Participants who meet the study-entry criteria will have up to 8 study visits. Repeat imaging studies may be required if the initial data are incomplete or un-interpretable. The maximum number of PET scans during the study will be limited to four.

Inclusion Criteria:

The prospective participant must meet, at least, all of the criteria below (among others determined by the study staff) to be eligible for study participation.

The participant:

• Has mild-to-moderate Alzheimer's Disease (AD), OR is considered cognitively normal;
• Has been on stable doses of any regularly used medications for 4 weeks prior to study start;
• Must have been on a stable dose for 12 weeks prior to study start, of any medications taken for AD.

Exclusion Criteria:

If the prospective participant meets any of the criteria below (among others determined by the study staff) they will NOT be eligible for study participation.

The participant:

• Is living in a nursing home or skilled nursing facility;
• Has severe AD;
• Cannot undergo MRI;
• Cannot undergo PET scans;
• Has a history of neurological or neurodegenerative disorders, other than AD within 2 years prior to study start;
• Has taken Tacrine or anti-parkinsonian medications within 3 months of study start;
• Has taken corticosteroids, blood thinners, narcotic analgesics, benzodiazepines, or certain antihistamines within 1 month of study start;
• Initiates, discontinues, or changes the dose of any AD treatment during the study.