Tau Tracer Comparison in Healthy Controls and Alzheimer's Disease Patients

This is an open label study to compare two new generation TAU radioligands, [18F]RO‐948 (formerly known as [18F]6958948) and [18F]MK‐6240, for imaging of tauopathy and demonstrate the radioligands' absence of off‐target binding in patients with Alzheimer's disease (AD) and older healthy controls (OC). The study will directly compare AD and OC with these two next‐generation TAU radio ligands and compare each of these radio ligands with the current most widely used first generation radioligand, [18F]AV‐1451. Up to 24 (12 AD and 12 OC, matched for age and sex with AD subjects) male and female subjects aged 50‐100 will be enrolled in the study. The study consists of three cohorts. ‐ Cohort 1: 10 AD subjects and 10 aged and sex matched older controls will be enrolled. Subjects will be scanned twice, with each of the tracers [18F]RO‐948 and [18F]MK‐6240. ‐ Cohort 2A: No positron emission tomography (PET) scans will be done. Previous [18F]AV‐1451 scans of selected aged matched OC subjects from the Baltimore Longitudinal Study of Aging (BLSA) study (IRB00047185) will be reanalyzed. ‐ Cohort 2B: 2 AD and 2 OC subjects who show high binding to the choroid plexus by a visual analog scale (high, low, and none) will be studied. Subjects will scanned twice with either: [18F]RO‐948 or [18F]MK‐6240 and a 2nd scan with [18F]AV‐1451 in randomized order and within one month of each other.