Cerebral HMPAO SPECT in patients with major depression and healthy volunteers.

1. The authors examined the regional cerebral distribution of [Tc-99m] HMPAO using single photon emission computed tomography (SPECT) in patients with major depression and in healthy controls. 2. 19 patients and 16 healthy controls had SPECT images of the brain acquired with 740 MBq (20 mCl) of [Tc-99m] HMPAO on a triple-headed camera equipped with fan beam collimators. 3. Mean counts per pixel were measured in 13 regions of each hemisphere and compared to the mean activity in the whole brain, the ipsilateral hemisphere, and cerebellum. A "laterality score" was calculated for each structure by subtracting the mean counts per pixel in a region of the right hemisphere from the mean counts in the homotopic region of the left hemisphere and normalizing the difference by the average in both regions. The degree of hemispheric asymmetry was calculated from the absolute values of the laterality scores. 4. The distribution of HMPAO was more variable in patients than in controls; while the mean activity ratios were not significantly different in any region. Asymmetries between homotopic regions of the limbic system were more pronounced in patients than in controls. However, there were no consistent left-to-right asymmetries in either group. 5. The present data indicate that regional cerebral distribution of HMPAO may not be discretely abnormal in depression, but demonstrates heightened variability in depressives (vs. control subjects).