Measurement of regional cerebral blood flow using one-point venous blood sampling and causality model. Evaluation by comparing with conventional continuous arterial blood sampling method

Optimal setting of the input function is essential for the measurement of regional cerebral blood flow (rCBF) based on the microsphere model using N-isopropyl-4-[123I]iodoamphetamine (123I-IMP), and usually the arterial 123I-IMP concentration (integral value) in the initial 5 min is used for this purpose. We have developed a new convenient method in which 123I-IMP concentration in arterial blood sample is estimated from that in venous blood sample. Brain perfusion single photon emission computed tomography (SPECT) with 123I-IMP was performed in 110 cases of central nervous system disorders. The causality was analyzed between the various parameters of SPECT data and the ratio of octanol-extracted arterial radioactivity concentration during the first 5 min (Caoct) to octanol-extracted venous radioactivity concentration at 27 min after intravenous injection of 123I-IMP (Cvoct). A high correlation was observed between the measured and estimated values of Caoct/Cvoct (r=0.856) when the following five parameters were included in the regression formula: radioactivity concentration in venous blood sampled at 27 min (Cv), Cvoct, Cvoct/Cv, and total brain radioactivity counts that were measured by a four-head gamma camera 5 min and 28 min after 123I-IMP injection. Furthermore, the rCBF values obtained using the input parameters estimated by this method were also highly correlated with the rCBF values measured using the continuous arterial blood sampling method (r=0.912). These results suggest that this method would serve as the new, convenient and less invasive method of rCBF measurement in clinical setting. (author)