Study Design: This is a cross-sectional study using the radiotracer 18F-AV-1451 to determine the relationship of tau pathology to both cross-sectional and longitudinal clinical and biomarker data of NACC cohort participants who are Cognitively Normal. All subjects will already be part of the longitudinal cohort study, known as the "NACC" cohort, of the PMC/ADC. For the current protocol, participants will provide informed consent before beginning any study procedures. After screening assessments, participants will undergo PET scan imaging with 18F-AV-1451.