MAPT and Alzheimer disease: For one reason, the progression of AD begins with an accumulation of amyloid, followed by the spread of tau beyond the temporal lobe, cerebral impairments, and, subsequently, deficits in glucose metabolism and, presumably, changes in rCBF.24,25 Therefore, the timing of conducting rCBF-SPECT and amyloid-PET scans can affect the findings of these examinations in assessing AD diagnosis.