Quantitative Measurement of Regional Cerebrovascular Reactivity to Acetazolamide Using 123I-N-Isopropyl-p-Iodoamphetamine Autoradiography with SPECT: Validation Study Using H2O with PET

A simplified technique using 123I-N-isopropyl-p-iodoamphetamine (123I-IMP) autoradiography (ARG) with SPECT has been proposed recently for quantifying regional cerebral blood flow (rCBF). To validate the accuracy of 123I-IMP-ARG for quantifying regional cerebrovascular reactivity (rCVR) to acetazolamide, we compared rCVR determined using 123I-IMP-ARG with that determined using H2O PET. Methods: Thirty-nine patients with chronic stenoocclusive disease in a unilateral major cerebral artery underwent SPECT and PET studies before and after intravenous administration of acetazolamide. The rCBF images in the 4 conditions in each patient were calculated according to the ARG method. The same standard input function and the same distribution volume of 35 mL/mL were used in the calculation of rCBF images using the 123I-IMP-ARG method at resting state and with acetazolamide challenge. One large cortical region of interest (ROI) for a unilateral middle cerebral artery territory was bilaterally determined on each standardized summed rCBF image. On the basis of the rCBF values in each ROI, rCVR to acetazolamide was calculated as follows: rCVR (%) ([acetazolamide challenge rCBF resting rCBF]/resting rCBF) 100. Results: Significant correlation was observed between rCVR values obtained using 123I-IMP-ARG and H2O PET methods in the 78 ROIs examined in the 39 patients (r 0.820; P 0.0001). When a rCVR lower than the mean 2 SD of values obtained in healthy volunteers (18.4% for 123I-IMPARG and 18.2% for H2O PET) was defined as reduced, and when the H2O PET method was assumed to represent the true determinant of rCVR, 123I-IMP-ARG was 90% sensitive and 92% specific and displayed an 87% positive predictive value for detecting patients with reduced rCVR. Conclusion: These findings demonstrate that 123I-IMP-ARG methods accurately quantify rCVR and can adequately define subgroups of patients with reduced rCVR.