MAPT and amyloidosis: Using a combination of amyloid and tau PET imaging, Biomarker Stage A is defined by positive amyloid and negative tau PET results; Stage B is defined by positive amyloid PET results and tau PET uptake restricted to the medial temporal lobe; Stage C is defined by positive amyloid PET results and moderate neocortical uptake on tau PET; and Stage D is defined by positive amyloid PET results and high neocortical tau PET uptake.