PURPOSE:The purpose of this study is to determine the value of Tc-99m HMPAO SPECT in the diagnosis of the dementias, with particular reference to Alzheimer disease. MATERIALS AND METHODS:Tc-99m HMPAO was used with a 3-camera scanner to produce 5 sets of sectional images of the brain. Diagnosis was made by a physician blinded to the clinical diagnosis. Results in 49 subjects were ultimately compared with neuropathologic study of the brain at autopsy. RESULTS:Sensitivity = 86.7% (68.4-95.6%, 95% confidence interval [CI]), specificity = 89.5% (65.5-98.2% CI), positive predictive value = 92.9% (75.0-98.8% CI), negative predictive value = 81% (57.4-93.7% CI), accuracy = 87.8% (74.5-94.9% CI), likelihood ratio = 8.23% (7.09-9.57% CI). CONCLUSIONS:Comparison is made with several other SPECT and PET series with histopathologic correlation. Brain blood flow SPECT is useful in the diagnosis and differential diagnosis of the dementias.