[Noninvasive quantitative measurement of cerebral blood flow with 123I-IMP--lung monitoring method].

In order to perform a less invasive determination of regional cerebral blood flow (rCBF) using I-123-IMP, we used the lung clearance curve as a substitute for the arterial blood activity curve as an input function. We assumed that a major portion of the intravenously injected I-123-IMP initially accumulates in the lung and then is gradually cleared from the lung pool to enter the systemic circulation. In this case lung clearance could be considered nearly equal to the integral of arterial blood activity shown during the examination. We used a single probe detector to obtain the lung clearance curve as the difference between sequential lung activity and peak lung activity. The absolute value of the sequential change in arterial blood activity was estimated from the differentiated lung clearance curve compared with the arterial blood activity that was estimated by actual blood sampling once during the examination. The rCBF was calculated by the thus estimated arterial blood activity curve and brain activity by SPECT image using the microsphere model. The values of rCBF obtained by this method were similar to those obtained by the continuous arterial sampling method, and this lung monitoring method was thought to be applicable to clinical use.