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

Abstract

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 15 O 2 . 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 15 O-water and C 15 O scans. Methods: Simulations were performed to assess the accuracy and precision of OEF for a variety of models in which different parameters from 15 O-water and C 15 O scans were reused. Reproducibility was assessed in 8 patients who underwent one 10-min dynamic scan after bolus injection of 1.1 GBq of 15 O-water, two 10-min dynamic scans after bolus inhalation of 1.4 GBq of 15 O 2 , and a 6-min static scan after bolus inhalation of 0.8 GBq of C 15 O for region-of-interest definition. Results: Simulations showed that accuracy and precision were lowest when all parameters were determined from the 15 O 2 scan. The optimal accuracy and precision of OEF were obtained when fixing MBF, perfusable tissue fraction, and blood spillover to values derived from a 15 O-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 15 O-water rather than C 15 O scan. Conclusion: Measurement of OEF is possible using bolus inhalation of 15 O 2 and a dynamic scan protocol, with optimal accuracy and precision when other relevant parameters, such as MBF, are derived from an additional 15 O-water scan. Oxygen extraction fraction (OEF) is an important parameter in describing myocardial function (1). Oxygen delivery to the healthy myocardium is regulated by varying myocardial blood flow (MBF) in response to changes in oxygen demand. In diseased myocardium, however, this relationship may be disturbed, and measurement of myocardial oxygen consumption could provide additional information, because oxygen supply to the heart may also be moderated by changes in OEF.Measurement of regional myocardial oxygen consumption has previously been described using steady-state or autoradiographic methods and applying continuous inhalation of 15 O 2 oxygen gas (1,2). Apart from the 15 O 2 scan, this protocol requires additional 15 O-water and C 15 O scans to measure MBF and blood volume, respectively. Many current low-energy proton cyclotrons, however, cannot provide a steady-state delivery of 15 O 2 to the patient. The availability of a bolus inhalation protocol would enable more widespread use of 15 O 2 gas measurements. Such a protocol has previously been described for cerebral oxygen consumption (3,4), but its use for myocardial imaging has not been described and presents several additional challenges, mainly because of increased scatter and...

Right Ventricular Failure in Idiopathic Pulmonary Arterial Hypertension Is Associated With Inefficient Myocardial Oxygen Utilization

“…11 We also measured RV perfusion, using H 2 15 O-PET next to OEF to calculate RV MVO 2 . 12 The purposes of this study were to (1) determine the relationship between RV power output and MVO 2 in IPAH patients and (2) relate RV mechanical efficiency to RV function, using both clinical and functional assessments in IPAH patients.…”

Supine-exercise-induced oxygen supply to the right myocardium is attenuated in patients with severe idiopathic pulmonary arterial hypertension

“…MBF was determined from these average time–activity curves using the standard single-tissue compartment model 17. The OEF of the RV myocardium was determined from the [ 15 O]O 2 scan using a novel implementation18 of a model previously described,16 in which RV MBF, perfusable tissue fraction, arterial blood volume and RV spillover were fixed to values determined from the [ 15 O]H 2 O scan and in which a correction for spillover from activity in the pulmonary gas volume was applied as described previously 19. The [ 15 O]O 2 input function was based on the volume of interest drawn in the ascending aorta and was corrected for the amount of recirculated water as measured in the arterial blood samples.…”

“…The calculation of OEF is described elsewhere 18. RV perfusion is the MBF of the free wall of the right ventricle.…”

11C-Acetate Clearance as an Index of Oxygen Consumption of the Right Myocardium in Idiopathic Pulmonary Arterial Hypertension: A Validation Study Using 15O-Labeled Tracers and PET

“…Analysis of 15 O data has been described in detail previously (5,12,14), and a brief description can also be found in the supplemental material. For the present study, the volume of interest was the RV free wall, excluding the septum.…”