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Constant-Infusion H₂¹⁵O PET and Acetazolamide Challenge in the Assessment of Cerebral Perfusion Status

¹ Division of Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland
² Department of Neurosurgery, University Hospital Zurich, Zurich, Switzerland

Assessing the baseline perfusion and perfusion reserve after acetazolamide (ACZ) challenge is a common method for the evaluation of patients with cerebrovascular disease. Most previous studies using H₂¹⁵O PET applied the bolus injection technique. There is considerable discrepancy regarding the optimal time point of imaging after ACZ injection. The purpose of this study was to continuously monitor cerebral blood flow (CBF) after ACZ using constant-infusion H₂¹⁵O PET. Methods: Four patients with stenoses of an internal carotid artery and 6 with moyamoya disease were studied. H₂¹⁵O was continuously infused, and data were recorded in 1-min frames. After equilibration of H₂¹⁵O, 5 min of baseline data were acquired, and then 1 g of ACZ was administered intravenously and data collection continued for 10–22 min. Arterial blood was continuously drawn for absolute quantification of CBF. Results: The arterial ¹⁵O concentration remained generally stable during scanning, and the cerebellar blood flow fluctuations of the 5 baseline scans were small. The scan-to-scan difference was 6% (difference of 2 successive scans/mean). In the nonpathologic areas, the increase in CBF started 1–2 min after administration of ACZ. The largest fraction of the increase occurred from 0 to 10 min. The ratio of CBF in pathologic areas to CBF in cerebellum showed an initial decrease that stabilized after 5 min. Conclusion: A continuous-infusion protocol is a viable alternative to single bolus injections for the assessment of cerebral perfusion status. Such a protocol is advantageous when the time course of CBF after an intervention is not known. With continuous monitoring, the optimal time point for evaluation of a certain parameter can be chosen post hoc. Furthermore, the time course of CBF itself may allow the definition of new parameters for evaluating perfusion status in cerebrovascular patients, both for assessment before a revascularization procedure and for follow-up. A limitation of the present study is the relatively small number of patients with each type of cerebrovascular disease and the lack of healthy subjects.

Key Words: PET • cerebral blood flow • acetazolamide • carotid stenosis • moyamoya disease

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