MAPT and supranuclear palsy, progressive, 1: One of the main challenges to reliably identify true tracer binding to 4-repeat tau aggregates characteristic of PSP and CBD by in vivo imaging is the consistently reported, although with variable intensity, elevated PET retention of [18F]-Flortaucipir, [18F]-MK-6240 and also [18F]-PI-2620 in the basal ganglia of older adults regardless of their clinical diagnosis [8].