The purpose of this research study is to evaluate a new radioactive compound used in positron emission tomography (PET) scans in identifying tau tangles (a certain protein that might be associated with Alzheimer's disease) in the brain, and if the amount of tau tangles in the brain has a relationship to cerebrospinal fluid (CSF) biomarkers and cognitive status.

This study involves a PET scans using the radioactive compound, F 18 T807 for measurement of tau deposition. This radioactive compound is not approved by the United States Food and Drug Administration (FDA). An MRI will be conducted if one has not been completed completed within the past 12 months under a related research study. Participants will be asked about their medical history, family history, surgical history, and current medications. We will evaluate history of traumatic brain injury (TBI) using the Ohio State University Traumatic Brain Injury Identification (OSU TBI-ID) Method. This will take approximately 10 minutes. Participants will be asked to undergo a Mini Mental State Examination (MMSE), which will last approximately 5-10 minutes.

Additionally, participants may be invited to undergo optional brain PET imaging with 2-deoxy-2-[18F]fluoro-D-glucose fludeoxyglucose (18F-FDG), for measurement of the cerebral metabolic rate of glucose consumption. At the time of the initial T807-PET study, participants will be asked if they are willing to undergo repeat T807-PET imaging at least 2 years after the initial study. This follow up study is optional, and participation in the study and initial T807-PET imaging will not be contingent on agreeing to the 2-year follow up study.

Inclusion Criteria:

1. Male or female participants, at least 65 years of age.
2. Participant is willing to undergo a lumbar puncture (LP) or has previously undergone LP. LP will be conducted under IRB ID 201109100 (PI: Anne Fagan).
3. Participant is able and willing to undergo positron emission tomography (PET) and magnetic resonance imaging (MRI) of the brain.
4. Pre-menopausal women must have a negative urine pregnancy test within 24 hours preceding T807 drug administration.

Exclusion Criteria:

1. Has any condition that, in the Investigator's opinion, could increase risk to the participant, limit the participant's ability to tolerate the experimental procedures, or interfere with the collection/analysis of the data (for example, participants with severe chronic back pain might not be able to lie still during the scanning procedures).
2. Is deemed likely unable to perform the imaging procedures for any reason.
3. Has a history of Torsades de Pointes or is taking medications known to prolong or may prolong QT interval (refer to study's list of restricted medications).
4. Has known hypersensitivity to T807 or any of its excipients.
5. Contraindications to PET, PET-CT or MR (e.g. electronic medical devices, inability to lie still for long periods) that make it unsafe for the individual to participate.
6. Severe claustrophobia.
7. Currently pregnant or breast-feeding. -

Under this study protocol, collaborating physicians and the Knight Alzheimer's Disease Research Center (ADRC) Clinical Core will refer participants to the Knight ADRC Research Imaging (KARI) Program for MR and PET imaging to evaluate tau distribution in the brains of cognitively normal and cognitively impaired individuals.

The Investigators may share the participant's data with other researchers that may be doing research in areas similar to this research or in other unrelated areas. These researchers may be at Washington University, at other research centers and institutions, or industry sponsors of research. The Investigators may also share the research data with large data repositories (a repository is a database of information) for broad sharing with the research community. If the individual research data is placed in one of these repositories only qualified researchers will be able to look at the information.