The purpose of this study is to investigate the radiotracer [11C] PIB in participants with probably Alzheimer's Disease (AD) and healthy age-matched controls.

The objectives of the study are:

1. To perform PET scans with [11C]PIB to use for direct (i.e., same-subjects) comparison of [11C]PIB and [18F]AV-45
2. To establish the most effective and reliable PET imaging method to detect amyloid deposition in AD, in order to understand disease progression and subsequently evaluate treatment effects.
3. To ascertain a PET imaging method that will minimize discomfort for subjects, thus increasing the potential for clinical follow-up scans, by reducing the patient burden and potential cost of future PET examinations.

A separate protocol/study will be conducted using [18F] AV-45. Participants who enroll in this protocol using [11C] PIB will be consented to participate in the [18F] AV-45 (IRB # NA_00033155) protocol/study as it is a mandatory requirement that participants participate in both protocols.Up to 20 participants with mild to moderate Alzheimer's Disease and 10 healthy volunteers will participate in this study.

Inclusion Criteria:

• Male or female subjects at least 18 years of age
• Subjects who in the opinion of the investigator based on medical history and physical exam can tolerate the PET scan procedures

Exclusion Criteria:

• Have clinically significant hepatic, renal, pulmonary, metabolic, or endocrine disturbances
• Have current clinically significant cardiovascular disease.
• Have a history of drug or alcohol abuse within the last year, or prior prolonged history of abuse
• Have a clinically significant infectious disease, including Acquired Immune Deficiency Syndrome (AIDS) or Human Immunodeficiency Virus (HIV) infection or previous positive test for hepatitis
• Women of childbearing potential must not be pregnant (negative urine beta-hCG at the time of screening and negative urine beta-hCG on the day of imaging) or lactating at screening or at day of imaging
• Have a history of relevant severe drug allergy or hypersensitivity (Relevant severe drug allergies should be determined by the PI, and any questions about a subject's eligibility can be directed to Avid. If a subject has a history of severe drug allergies, it may be dangerous for them to participate in a study with a novel compound
• Have received an investigational medication within the last 30 days. Current clinically significant or unstable medical comorbidities, as indicated by history or physical exam
• Have received a radiopharmaceutical for imaging or therapy within the past 7 days prior to the imaging session for this study
• Body weight > 300 pounds
• History of significant radiation exposure
• Participants with pacemakers, implanted electronic hearing devices, aneurysm clips, shrapnel, unallowed prosthetic or other metallic device in their bodies
• Pre-existing CNS disease (other than dementia), endocrine, or severe cardiovascular disease (MI, CABG, angioplasty)