A Study to Assess Regional Cerebral Blood Flow as an Alzheimer's Disease Biomarker Compared to Positron Emission Tomography in Patients With Mild-to-Moderate Alzheimer's Disease and Cognitively Normal Elderly Subjects (Study MK-0000-068)(COMPLETED)

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.