Tau PET/CT Imaging in the Mismatch Prospective Cohort Study (MPC-TAU)

Inclusion Criteria: 1. Enrolled in MPC study (Protocol 850160 at UPenn; Protocol 2022P002447 at MGH). 2. Reliable study partner to accompany participant to the PET/CT scan 3. A brain MRI must be performed within 6 months prior to their study AV-1451 TAU PET/CT scan date and be deemed of adequate quality that the scan may be used for study analysis, including 3T high-resolution imaging of medial temporal lobe structures. Exclusion Criteria: 1. 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. 2. Have evidence of structural abnormalities such as major stroke or mass on MRI that is likely to interfere with analysis of the PET/CT scan. 3. Inability to tolerate or contraindication to imaging procedures in the opinion of an investigator or treating physician. 4. Have a history of significant ongoing alcohol or substance abuse based on self- report. 5. Female participants of child-bearing age will not be able to participate in this study, determined by self-report.