Measurement of myocardial oxygen extraction fraction using bolus inhalation of 15O-oxygen and dynamic PET

Objectives The aim of this study was to determine accuracy of oxygen extraction fraction (OEF) measurements using either a single scan after bolus inhalation of ¹⁵O₂ to determine OEF, flow (MBF), and perfusable tissue fraction (PTF) or a ¹⁵O₂ scan combined with a separate H₂¹⁵O scan for determination of MBF and PTF.

Methods Simulations were performed to assess accuracy and precision of OEF when determining (A) all parameters from ¹⁵O₂, (B) OEF from ¹⁵O₂ and MBF and PTF from H₂¹⁵O, and (C) all parameters from ¹⁵O₂, but restricting MBF and PTF to within ±10% of values derived from H₂¹⁵O to account for minor changes between the scans. Three patients underwent a 10 min scan on an ECAT Exact HR+ scanner after bolus injection of 1.1 GBq H₂¹⁵O, two 10 min scans after bolus inhalation of ~ 1.4 GBq ¹⁵O₂, and a 6 min static scan after bolus inhalation of ~ 0.8 GBq C¹⁵O for ROI definition.

Results Simulations showed highest correlation between simulated and true OEF for model B (r² 0.96 vs. 0.56 and 0.88 for A and C, respectively), with no bias. If small differences in parameters were present between H₂¹⁵O and ¹⁵O₂ scans, correlation was best for model C (r² 0.88 vs 0.56 and 0.82 for A and B). In patients best fits were obtained for model B. Whole myocardium test-retest accuracy of OEF was 14±7%.

Conclusions Best accuracy and precision for myocardial OEF measurements following bolus inhalation of ¹⁵O₂ are obtained when other necessary parameters, such as MBF, are derived from an additional H₂¹⁵O scan.