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A New Graphic Plot Analysis for Cerebral Blood Flow and Partition Coefficient with Iodine-123-Iodoamphetamine and Dynamic SPECT Validation Studies Using Oxygen-15-Water and PET

Department of Research for Nuclear Medicine, Medical Systems Division, Shimadzu Corporation, Kyoto, Japan
Department of Radiology and Nuclear Medicine, Research Institute for Brain and Blood Vessels, Akita, Japan

Correspondence: For correspondence or reprints contact: Takashi Yokoi, Dept. of Research for Nuclear Medicine, Medical Systems Division, Shimadzu Corporation, 1 Nishinokyo-Kuwabaracho Nakagyo-ku, Kyoto 604, Japan

ABSTRACT

To estimate regional cerebral blood flow (rCBF) and brain blood partition coefficient () using a dynamic measurement, a new graphic plot analysis is proposed. By assuming a two-compartment model for tracer kinetics, we derived the linear relationship as Y(t) = K₁ – k₂ X(t), where Y(t) is the ratio of brain tissue activity-to-time-integrated arterial blood activity and X(t) is the ratio of time-integrated brain tissue activity-to-time-integrated arterial blood activity. A plot of Y(t) against X(t) yields a straight line and the y- and x-intercept of the regression line represent rCBF (K₁) and , respectively. The slope is a washout constant (–k₂). This method was applied to 14 subjects with N-isopropyl-p-iodine-123 iodoamphetamine ([¹²³I]IMP). The mean values of K₁ and for normal subjects were 41.3 ± 6.7 ml/100 g/min and 29.6 ± 6.5 ml/g, respectively, in the gray matter. A comparative study with positron emission tomography (PET) using an H₂¹⁵O autoradiographic method revealed good correlation between IMP K₁ and PET rCBF [r = 0.822; K₁ = 0.842 rCBF + 0.030 (ml/g/min)]. The values of K₁ using the graphical method were in excellent agreement with those using a nonlinear least-squares fitting technique (r = 0.992 for K₁; r = 0.941 for ). The estimated K₁ values in the graphical method were not changed when scanning times were varied. We conclude that a two-compartment model is acceptable for IMP kinetics within a scan time of 60 min. The graphical method gives a reliable and rapid estimation of rCBF when applied to dynamic data.