Comparison between cortical distribution of I-123 iomazenil and Tc-99m HMPAO in patients with Alzheimer's disease using SPECT.

PURPOSE

To compare brain perfusion and synaptic density in Alzheimer's disease assessed using I-123 iomazenil SPECT with brain perfusion assessed using Tc-99m HMPAO SPECT.

MATERIALS AND METHODS

Early and delayed I-123 iomazenil SPECT images acquired 20 and 180 minutes after injection were compared with Tc-99m HMPAO SPECT studies acquired 15 to 20 minutes after injection in five patients with Alzheimer's disease.

RESULTS

Visual analysis of I-123 iomazenil images showed more severe (n = 4) and extensive (n = 3) defects than did Tc-99m HMPAO. Semiquantitative analysis was performed by normalizing the uptake of Tc-99m HMPAO and I-123 iomazenil in individual brain regions in the cerebellum and expressing these values as a ratio of the occipital regions. The analysis of brain regional ratios in Tc-99m HMPAO studies showed a low but significant correlation with ratios of delayed (r = 0.325, P < 0.05) images in the I-123 iomazenil studies. Furthermore, when compared with Tc-99m HMPAO, early (P < 0.01) and delayed mean ratios (P < 0.05) were significantly less in the frontal regions; early mean ratios were significantly less in the temporal regions (P < 0.05), and delayed (P < 0.05) mean ratios were significantly less in the parietal regions.

CONCLUSIONS

Tc-99m HMPAO images were better correlated with I-123 iomazenil images, indicating cortical synaptic density (delayed images). I-123 iomazenil SPECT in patients with Alzheimer's disease provided more sensitive information than Tc-99m HMPAO, allowing evaluation of brain perfusion and synaptic density.