RecruitingDrug trialTau PET/CT Imaging in the Mismatch Prospective Cohort Study (MPC-TAU)To collect Tau PET/CT imaging in older adults diagnosed with Mild Cognitive Impairment (MCI) or Alzheimer's Disease (AD) in the Mismatch Prospective Cohort Study (MPC-Tau) study to determine relationship to clinical, cognitive, and other biomarker data. Findings from this study will likely provide insight into the phenotypic variability of Alzheimer's Disease and other related pathologies.