MAPT and Classical progressive supranuclear palsy: We used a new data-driven methodology to identify a set of reference regions that enhanced the quantification of the SUV ratio of the second-generation tau tracer 2-(2-([18F]fluoro)pyridin-4-yl)-9H-pyrrolo[2,3-b:4,5-c′]dipyridine ([18F]PI-2620) in a group of patients clinically diagnosed with 4-repeat tauopathy, specifically progressive supranuclear palsy or cortical basal syndrome.