Purpose: Although (15)O-O(2) gas inhalation can provide a reliable and accurate myocardial metabolic rate for oxygen by PET, the spillover from gas volume in the lung distorts the images. Recently, we developed an injectable method in which blood takes up (15)O-O(2) from an artificial lung, and this made it possible to estimate oxygen metabolism without the inhalation protocol. In the present study, we evaluated the effectiveness of the injectable (15)O-O(2) system in porcine hearts.
Methods: PET scans were performed after bolus injection and continuous infusion of injectable (15)O-O(2) via a shunt between the femoral artery and the vein in normal pigs. The injection method was compared to the inhalation method. The oxygen extraction fraction (OEF) in the lateral walls of the heart was calculated by a compartmental model in view of the spillover and partial volume effect.
Results: A significant decrease of lung radioactivity in PET images was observed compared to the continuous inhalation of (15)O-O(2) gas. Furthermore, the injectable (15)O-O(2) system provides a measurement of OEF in lateral walls of the heart that is similar to the continuous-inhalation method (0.71 +/- 0.036 and 0.72 +/- 0.020 for the bolus-injection and continuous-infusion methods, respectively).
Conclusion: These results indicate that injectable (15)O-O(2) has the potential to evaluate myocardial oxygen metabolism.