We developed and evaluated a simplified double-injection method for iodine-123 N-isopropyl-p-iodoamphetamine (IMP) to quantify regional cerebral blood flow (rCBF) twice in a single SPECT session. The method enabled rapid calculations of rCBF with five 10-minute SPECT scans, a fixed distribution volume (Vd), and one-point arterial blood sampling to calibrate a standard input function (SIF).
Methods: Sixty neurological patients were examined to measure rCBF twice in a single session of IMP-SPECT. Patients underwent frequent arterial blood sampling with two injections of IMP and acetazolamide challenge. We generated the SIF and determined the optimal Vd and calibration time (t(cal)) for the SIF in 30 patients. Validities of the fixed t(cal) and Vd were assessed in the remaining 30 patients. Simulation studies were also performed to evaluate the error sensitivity of the method.
Results: The optimal t(cal) and Vd were 34 min and 30 ml/ml, respectively. The method was robust in rCBF calculation with noisy SPECT data and yielded rCBF with negligible bias and acceptable errors compared with those obtained by the double-injection method previously reported.
Conclusion: The method can be applied to measure rCBF twice in a single SPECT session more easily and less invasively.