ABSTRACT
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 99mTc-HMPAO SPECT studies in unmedicated patients with schizophrenia and major depression are discussed in the light of 99mTc-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