Theoretical and experimental assessment of the kinetic properties of N-isopropyl-p-[123I]iodoamphetamine in the human brain.

The effect of the loss of radioactivity from the human brain on the measurement of regional cerebral blood flow (rCBF) using N-isopropyl-p-[123I]iodoamphetamine (IMP) was evaluated by measuring rCBF in 10 normal male volunteers from 0.5 to 30 minutes after intravenous administration. rCBF was calculated by the operational equation, which assumes no product loss. Brain tissue and arterial blood concentration data were plotted according to a multiple-time/graphic evaluation technique. Data were fitted to the kinetic three-compartment model to estimate four kinetic rate constants to evaluate activity loss from the brain. These studies showed that loss of activity from the brain is negligible during the first 5 minutes, but after 7.5 minutes the loss becomes significantly higher with time. The present study corroborates the necessity for using single photon emission computed tomographic images measured within 5 minutes of IMP injection to quantify rCBF.