Acetazolamide Reactivity on ¹²³I-IMP Single Photon Emission Computed Tomography in Patients with Major Cerebral Artery Occlusive Disease: Correlation with Positron Emission Tomography Parameters

Single photon emission computed tomography (SPECT) with acetazolamide challenge has increasingly been used for evaluating hemodynamic reserve in stroke patients. The accuracy of this test, however, has not been validated with positron emission tomography (PET). In 14 patients who had occlusive disease of the internal carotid artery or the trunk of the middle cerebral artery (MCA) with minimal or no infarction on computed tomography (CT) and magnetic resonance imaging (MRI), we compared acetazolamide reactivity on SPECT with N-isopropyl-p-[123I]-iodoamphetamine to hemodynamic parameters determined with gas inhalation labeled 15O steady-state PET studies. The asymmetry index (AI)--i.e., the percentage of the activity rate of the ischemic MCA territory versus the contralateral one, was determined by SPECT. Acetazolamide reactivity expressed as delta AI, or change in AI after acetazolamide challenge, was significantly lower in seven patients than -8.4%, the lower limit of the 95% confidence interval for the normal reactivity. Values of ipsilateral CBF, cerebral blood volume (CBV)/CBF, and oxygen extraction fraction (OEF) and contralateral OEF were significantly different between patients with normal and reduced acetazolamide reactivity. Values of delta AI were correlated with OEF (r = -0.87; p < 0.001) and CBV/CBF (r = -0.56; p < 0.05). All patients with OEF > 0.52, the mean + 2 SD calculated from five normal volunteers, also had reduced acetazolamide reactivity, while the patients with normal OEF values had normal reactivity. The present study has demonstrated that SPECT studies with an acetazolamide challenge can detect the Stage II hemodynamic failure.