The study employs tau positron emission tomography (PET) imaging in a well-characterized multi-racial/ethnic cohort to examine the extent to which tau pathology is associated with cognition, differences in tau pathology across racial/ethnic groups, and the relationship between MRI markers of small-vessel cerebrovascular disease and tau pathology. The study also investigates amyloid-dependent tau spreading.

Deposition of hyperphosphorylated tau protein is observed in several neurodegenerative diseases including Alzheimer's Disease (AD), progressive supranuclear palsy, corticobasal degeneration, chronic traumatic encephalopathy, and frontotemporal lobar degeneration. Tau is a microtubular protein and its native function is to provide structural support to neurons. Paired helical filaments composed of dysfunctional tau protein are found in several neurodegenerative diseases. In AD, the clinical progression of dementia has been shown to correlate with the amount and topographical spread of tau throughout the brain. Therefore, detecting and quantifying tau aggregate load in brain would have diagnostic and prognostic potential in clinical management of several neurological diseases. As disease modifying drugs that target tau are being developed, there is a critical need for a reliable method of detecting tau aggregates to confirm pathology in patients entering clinical trials.

Inclusion Criteria:

• Aged 35 - 85 years
• Have either mild cognitive impairment or mild clinical Alzheimer's disease; or have no problem with memory or thinking.
• Able to participate in all scheduled evaluations and to complete all required tests and procedures
• Considered likely to comply with the study protocol and to have a high probability of completing the study

Exclusion Criteria:

• Past or present history of a certain brain disease other than mild cognitive impairment or mild clinical Alzheimer's disease.
• Certain significant medical conditions. Examples are uncontrolled epilepsy or multiple serious injuries.
• Unable to lie still for PET scans.
• Radiation exposure for research studies in the last year that would put you past allowable limits if included in this study.
• Participation in the last year in a clinical trial for a disease modifying drug for AD unless it can be determined that your received placebo and not active drug.
• Conditions that preclude entry into the scanner (e.g. claustrophobia, etc.).
• Inability to have a catheter in your vein for the injection of the radioligand (dye).
• Currently pregnant or breastfeeding.

Analyses are planned to be on the group level. However, we may emphasize cases that are interesting on the individual level.

Of the 145 participants who consented to be in the study, 3 participants withdrew prior to receiving any scan. No baseline data was collected from these 3 participants.

1 day for each scan, within 24 months of each other