MAPT and Alzheimer disease: The ability of [18F]AV1451 to detect 4R-tau isoforms, predominant in CBS and PSP, has been debated with autoradiography studies showing lower binding of [18F]AV1451 in non-AD brains compared to AD (Marquie et al. 2015; Sander et al. 2016; Lowe et al. 2016).