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The aim of this SPECT study was to determine the initial abnormality and longitudinal changes in regional cerebral blood flow (rCBF) in early Alzheimer's disease (AD) using statistical parametric mapping (SPM). rCBF was noninvasively measured using 99mTc-ethylcysteinate dimer SPECT in 32 patients complaining of mild cognitive impairment, with a Mini-Mental State Examination score more than 24 at the initial study, and 45 age-matched healthy volunteers. All patients satisfied the diagnostic criteria of AD during the follow-up period of at least 2 y. Follow-up SPECT studies were performed on the patients at a mean interval of 15 mo. We used the raw data (absolute rCBF parametric maps) and the adjusted rCBF images of relative flow distribution (normalization of global cerebral blood flow [CBF] for each subject to 50 mL/100 g/min with proportional scaling) to compare these groups with SPM.