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.
The primary objective of this study is to identify a new radioligand for imaging of tauopathy in Alzheimer's disease through direct comparisons of two potential candidates, [18F]RO-948 (formerly known as [18F]6958948) and [18F]MK-6240, and demonstration of the candidates' absence of off-target binding.