A method for estimating the integral of the input function for the quantification of cerebral blood flow with ¹²³i-imp using one-point arterial blood sampling

We have developed a new method to replace the conventional method of quantitatively measuring cerebral blood flow (CBF), in which octanol-extracted radioactivity counts are measured in continuous arterial blood samples. With the new method, the whole-brain time-activity curves early after the intravenous injection of N-isopropyl-p-[¹²³I] iodoamphetamine were first obtained by the least-squares curve-fitting method. The equation thus obtained was differentiated and the radioactivity counts were corrected by the 5-min octanol-extracted radioactivity counts of the arterial blood sample obtained at a single time point. In the present study, the value obtained by integrating the equation from 0 to 5 min, which was obtained by curve-fitting, was compared with the octanol-extracted radioactivity counts obtained by 5-min continuous arterial blood sampling in 160 patients with cerebrovascular disorders. The results showed good agreement between the values obtained by the two procedures (y = 1.049 x - 1522.4; r = 0.987). Using the CBF obtained by the 5-min continuous arterial blood sampling as the standard, the errors using the present integral values of the input function were 7.1 ± 4.9%. Measurements of the integral of the input function by the present one-point arterial blood sampling method has the potential for use in the routine measurement of CBF, because it is less invasive and more convenient than the conventional method, and it is unaffected by cardiopulmonary disease or smoking.