Relationship of apparent myocardial T2 and oxygenation: towards quantification of myocardial oxygen extraction fraction.

Abstract

To explore the relationship of myocardial T(2) and oxygenation for the quantification of myocardial oxygen extraction fraction (OEF). A proposed myocardial T(2)-OEF relationship was evaluated by computer simulation and in nine normal dogs in vivo. The relationship was based on a simplified two-compartment T(2) model. In the dogs, dipyridamole was infused intravenously to increase blood flow and change in myocardial oxygen content. The accuracy of the measurement in myocardial OEF in vivo by magnetic resonance imaging (MRI) was determined by arterial and coronary sinus blood sampling. Global myocardial T(2) increased 16.1% from rest to the peak of dipyridamole-induced vasodilation (44.6 +/- 2.1 msec vs. 51.4 +/- 2.1 msec, P < 0.001). Corresponding OEF measured by arterial and venous (AV) sampling decreased from 0.64 +/- 0.15 at rest to 0.18 +/- 0.08 during the dipyridamole vasodilation, whereas OEF calculated by MRI at the peak effect of dipyridamole was 20 +/- 4%. Global myocardial OEF measured dynamically by MRI showed a strong correlation with OEF measured by blood sampling (correlation coefficient (CC) = 0.83) during pharmacologic vasodilation. When combined with vasodilator stress, assessment of OEF may provide a putative measure of myocardial flow reserve, allowing consecutive monitoring of myocardial dose-responses to a variety of interventions and offering a new tool for the detection of coronary artery disease.