A blinded read of images obtained with 99mTc-bicisate and single photon emission computed tomography (SPECT) was conducted to determine if a relationship exists between the severity of abnormalities on SPECT brain images and the severity of cognitive impairment in patients with dementia of the Alzheimer type (DAT) and to examine the interreader agreement for visual reading of images in a multicenter SPECT study. Images for a total of 86 subjects were available for the blinded read. The images for 28 subjects were rated as noninterpretable due to technical inadequacies. Images for 58 subjects (45 DAT patients and 13 normal volunteers) from 10 SPECT centers were selected for further analyses. The severity of abnormality was rated as mild, moderate, or severe by three readers. In DAT patients, a significant negative correlation (p < 0.05) of Mini-Mental State Examination (MMSE) score with global severity of abnormality was noted for two of the three readers. A significant correlation (p < 0.05) between MMSE score and severity of abnormality was observed for all three readers for the posterior temporoparietal region. The blinded readers rated a median of 92.3% of normal volunteers' images as normal and a median of 82.2% of DAT patients' images as abnormal. For the regional severity of abnormality, the median percentage interrater agreement across all regions ranged from 95 to 100% in normal volunteers and from 81 to 98% in DAT patients. These results suggest that SPECT brain imaging with 99mTc-bicisate provides functional information about the severity of cognitive impairment in DAT patients.(ABSTRACT TRUNCATED AT 250 WORDS)