Linking Tau PET to Medial Temporal Lobe Subregions With High Resolution MRI

Inclusion Criteria: * Males and females ≥ 60 years of age. * Part of the NACC longitudinal cohort (IRB# 068200) of the PMC/ADCC with consensus conference designation of cognitively normal or Mild Cognitive Impairment (MCI) or Alzheimer's Disease (AD) Possible or Probable. * NACC longitudinal visit completed or scheduled within 6 months before or after enrollment in this study. * Women must be post-menopausal or surgically sterile. * An amyloid PET scan, completed as a part of the NACC protocol (IRB# 825943), must be performed or scheduled within 12 months before or after the \[18F\]PI-2620 PET scan. * A brain MRI, completed as a part of NACC protocol (IRB# 068200), must be performed or scheduled within 6 months before or after the \[18F\]PI-2620 PET scan. Scan should be of adequate research quality, including 3 Tesla and/or 7 Tesla high-resolution imaging of MTL structure. Exclusion Criteria: * Have any medical or psychiatric conditions that, in the opinion of the investigator, would compromise the subject's safety or successful participation in the study. * Have evidence of structural abnormalities such as major stroke or mass on MRI that is likely to interfere with analysis of the PET scan. * Inability to tolerate or contraindication to imaging procedures in the opinion of an investigator or treating physician. * Have a history of significant or ongoing alcohol abuse or substance abuse or dependence based on medical record review or self-reported. The inclusion / exclusion criteria will be ascertained through self-report in conjunction with any medical history available through the participant's medical or research records (EPIC or the ADC database)