Qualitative versus quantitative assessment of cerebrovascular reactivity to acetazolamide using iodine-123-N-isopropyl-p-iodoamphetamine SPECT in patients with unilateral major cerebral artery occlusive disease

BACKGROUND AND PURPOSE: Qualitative measurement of regional cerebrovascular reactivity (rCVR) to acetazolamide with single-photon emission CT (SPECT) has been widely used to determine the severity of hemodynamic impairment. We attempted to validate the accuracy of qualitative assessment by using SPECT to detect reduced rCVR compared with rCVR determined quantitatively in patients with unilateral major cerebral artery occlusion. METHODS: Regional cerebral blood flow was assessed with iodine-123-N-isopropyl-p-iodoamphetamine ((123)I-IMP) at rest and after acetazolamide activation in 133 patients with previously symptomatic, unilateral internal carotid or middle cerebral artery occlusion. Quantitative values were calculated by using the (123)I-IMP autoradiographic method and analyzed for each cerebral hemisphere as the percentage change in rCBF between resting and activation studies (%(Hem)). Qualitative rCVR was determined for the target hemisphere distal to the occlusion as the cerebral-interhemispheric asymmetry index (AI(Hem)) and as an index of flow difference between the target cerebral and ipsilateral cerebellar hemispheres (FI(Hem-Cbl)). Values 2 SDs below the mean in healthy volunteers were defined as decreased. RESULTS: Fair agreement was observed between %(Hem) and both AI(Hem) change (resting vs activation, kappa = 0.409) and FI(Hem-Cbl) change (resting vs activation, kappa = 0.440). When %(Hem) was assumed to represent the true determinant of assessing rCVR, AI(Hem) change and FI(Hem-Cbl) change demonstrated sensitivities of 68% and 78%; specificities, 72% and 76%; positive predictive values, 48% and 56%; false-positive incidences, 28% and 24%; and false-negative incidences, 32% and 22% for detecting patients with reduced rCVR, respectively. CONCLUSION: Subgroups of patients with hemodynamic impairment cannot be accurately defined by using rCVR qualitatively measured with SPECT.