SPECT measurement of regional cerebral blood flow using N-isopropyl-p-(123I) iodoamphetamine

Single photon emission computed tomography (SPECT) using N-isopropyl-p-(123I) iodoamphetamine (IMP) as a flow tracer is widely used to estimate regional cerebral blood flow (rCBF). However, the tracer kinetics of IMP in the brain has not been fully evaluated and the significance of the 'late image' is not clear yet. The present study was made to elucidate the tracer kinetics of IMP, to assess the accuracy of calculated rCBF and to clarify the role of the late image. Radioactivity in the artery and in the jugular vein was measured after intravenous injection of IMP. In healthy volunteers the extraction rate of IMP from the blood to the brain was 79.3%, a lower rate than that reported so far. IMP metabolites were also found to be extracted by the brain. These results suggest that in calculating the absolute value of rCBF, corrections must be appropriated for the extraction rate of IMP and metabolites. In patients with cerebrovascular disease (CVD), a correlation was observed between a good prognosis and late images showing a densely filled ischemic area; and, conversely, a sparse filling or hyperactivity was associated with a poor prognosis. Consequently, the late image is thought to be useful in estimating the prognosis of CVD. (author)