A PET-based subtyping of bvFTD. (A) Representative axial (left) and coronal (right) images of radioactivity SUVRs at 90–110 min after ¹⁸F-florzolotau administration. The arrowheads of normal size indicate enhanced parenchymal radioligand retentions characteristic of each putative tau topology subtype. The smaller arrowheads denote radioactivity accumulations in the choroid plexus supposedly unrelated to tau depositions. Radio signal intensification primarily in the frontal and temporal cortices in contrast to relative sparing of posterior and subcortical areas is indicative of Pick’s disease–type 3RT aggregations (P03), while involvements of subcortical regions, including the basal ganglia, thalamus, subthalamic nucleus and brainstem, suggest PSP- or CBD-type 4RT lesions (P04). The negativity for ¹⁸F-florzolotau-PET implies non-tau bvFTD exemplified by Type A TDP-43 pathologies (P11). A case with Aβ-PET–positive exhibited limbic and neocortical radioligand accumulations involving temporo-parietal regions and is accordingly granted a clinicopathological phenotype of bvFTD due to Alzheimer’s disease pathologies (P15). (B) A subgrouping of 15 cases with bvFTD by the visual read of individual tau PET images. Patients P01–P03 showed predominant ¹⁸F-florzolotau accumulations in the frontotemporal and frontolimbic cortices with minimal posterior cortical involvements suggestive of 3RT pathologies. P01 is a case with autopsy-confirmed Pick’s disease. P04–P07 presented increased radioligand retentions in subcortical structures accompanied by neocortical involvements to varying degrees, implying the presence of 4RT depositions. P08–P11 displayed no overt radioligand accumulations. P12–P15 were Aβ-positive, and the distribution of radio signals followed Braak tau staging consistent with Alzheimer’s disease. In each subject, three axial, one coronal and one sagittal sections providing characteristic information are presented from the left. A, anterior; L, left; P, posterior; R, right.