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Myocardial Oxygen Extraction Fraction Measured Using Bolus Inhalation of 15O-Oxygen Gas and Dynamic PET

The aim of this study was to determine the accuracy of oxygen extraction fraction (OEF) measurements using a dynamic scan protocol after bolus inhalation of 15O2. The method of analysis was optimized by investigating potential reuse of myocardial blood flow (MBF), perfusable tissue fraction, and blood and lung spillover factors derived from separate 15O-water and C15O scans. Methods: Simulations were performed to assess the accuracy and precision of OEF for a variety of models in which different parameters from 15O-water and C15O scans were reused. Reproducibility was assessed in 8 patients who underwent one 10-min dynamic scan after bolus injection of 1.1 GBq of 15O-water, two 10-min dynamic scans after bolus inhalation of 1.4 GBq of 15O2, and a 6-min static scan after bolus inhalation of 0.8 GBq of C15O for region-of-interest definition. Results: Simulations showed that accuracy and precision were lowest when all parameters were determined from the 15O2 scan. The optimal accuracy and precision of OEF were obtained when fixing MBF, perfusable tissue fraction, and blood spillover to values derived from a 15O-water scan and estimating spillover from the pulmonary gas volume using an attenuation map. Optimal accuracy and precision were confirmed in the patient study, showing an OEF test–retest variability of 13% for the whole myocardium. Correction of spillover from pulmonary gas volume requires correction of the lung time–activity curve for pulmonary blood volume, which could equally well be obtained from a 15O-water rather than C15O scan. Conclusion: Measurement of OEF is possible using bolus inhalation of 15O2 and a dynamic scan protocol, with optimal accuracy and precision when other relevant parameters, such as MBF, are derived from an additional 15O-water scan.