Simplified quantitative determination of cerebral perfusion reserve with H2 15O PET and acetazolamide

The measurement of regional cerebral blood flow (rCBF) and perfusion reserve (PR) with H₂¹⁵O positron emission tomography (PET) and acetazolamide challenge is of importance in evaluating patients with cerebrovascular disease and is thought to be useful in selecting patients for possible vascular surgery. Full quantitative assessment of rCBF with PET requires arterial blood sampling, which is inconvenient in a clinical setting. In this work, we present a simple non-invasive method with which to quantitatively evaluate PR in one PET session lasting no more than 30 min. In ten patients with cerebrovascular disease, rCBF was measured with H₂¹⁵O PET under the baseline condition and after administration of 1 g acetazolamide using a standard technique involving arterial blood sampling. The activity accumulated over 60 s was normalized to injected activity per kilogram body weight (nAA) and compared with rCBF in eight different brain regions. A high linear correlation was found for PR based on nAA (PR_nAA) and rCBF (PR_rCBF) (PR_nAA=0.843 PR_rCBF + 0.092, r=0.83, Pearson's correlation coefficient). Bland-Altman analyses further confirmed that PR_nAA reflects PR in a quantitative manner. These results demonstrate that the method based on normalized counts allows the quantitative assessment of PR without blood sampling.