MAPT and Alzheimer disease: There was high binding of [18F]PI-2620 (Figure 7f) in the substantia nigra and globus pallidus in PSP patients compared with HCs, implying binding to 4R tau filaments, but the binding was higher still in the cortex of AD patients; highest tracer retention in Aβ+ AD patients was in the posterior cingulate gyrus and temporoparietal areas.