The origin of altered radiotracer uptake and distribution in functional brain imaging studies, often
considered to reflect regional cerebral blood flow (rCBF), in psychiatric disorders is unknown. Interpreting
the magnitude of changes as changes in the magnitude of neuronal activity may be reasonable during
normal circumstances, but less reliable in pathologic states. Results of published
99m
Tc-HMPAO SPECT
studies in unmedicated patients with schizophrenia and major depression are discussed in the light of
99m
Tc-HMPAO properties, and reported findings of altered cell morphology and biochemistry, with emphasis
on energy metabolism. We conclude that the SPECT technique using radiotracers with known biochemical
properties will become useful in the understanding of cellular dysfunctions at different phases of
neuropsychiatric disorders, and that use of automatic interpretation of three-dimensional volumes will allow
for easier identification of regional neural correlates of the different psychiatric symptoms.
