[Quantification of cerebral blood flow using 123I-IMP SPECT--a new method of estimating the input function from brain...

In order to avoid continuous arterial blood sampling, we estimated input function by the method in that the whole brain time activity curves were fitted by two-term exponential function and differentiated analytically after the injection of N-isopropyl-p-[123I]iodoamphetamine (123I-IMP). This method was applied to 4 patients with cerebral infarction and 2 patients with brain tumor. Values of regional cerebral blood flow (rCBF) were calculated from the input function calibrated by one-point arterial sampling at 5 minutes after the injection using microsphere method, and then were compared with those obtained from the table-lookup method. In this study, we used the individual input function for the table-lookup method instead of the standard input function. The overall accuracy errors between two-term exponential functions and the whole brain time-activity curves were about 1%. The values of rCBF calculated by this method were well correlated with those by the table-lookup method (r = 0.901, p < 0.001). Optimal calibration time for this method was between 3-minute and 10-minute after 123I-IMP injection and the deviation of the rCBF values obtained by this method from those obtained by the table-lookup method in which the input function was calibrated at 5 minutes remained within 10%. This method is a less invasive and convenient alternative to the conventional methods which require continuous arterial blood sampling.