Quantification of global myocardial oxygenation in humans: initial experience

To assess the feasibility of our newly developed cardiovascular magnetic resonance (CMR) methods to quantify global and/or regional myocardial oxygen consumption rate (MVO₂) at rest and during pharmacologically-induced vasodilation in normal volunteers.

A breath-hold T₂ quantification method is developed to calculate oxygen extraction fraction (OEF) and MVO₂ rate at rest and/or during hyperemia, using a two-compartment model. A previously reported T₂ quantification method using turbo-spin-echo sequence was also applied for comparison. CMR scans were performed in 6 normal volunteers. Each imaging session consisted of imaging at rest and during adenosine-induced vasodilation. The new T₂ quantification method was applied to calculate T₂ in the coronary sinus (CS), as well as in myocardial tissue. Resting CS OEF, representing resting global myocardial OEF, and myocardial OEF during adenosine vasodilation were then calculated by the model. Myocardial blood flow (MBF) was also obtained to calculate MVO₂, by using a first-pass perfusion imaging approach.

The T₂ quantification method yielded a hyperemic OEF of 0.37 ± 0.05 and a hyperemic MVO₂ of 9.2 ± 2.4 μmol/g/min. The corresponding resting values were 0.73 ± 0.05 and 5.2 ± 1.7 μmol/g/min respectively, which agreed well with published literature values. The MVO₂ rose proportionally with rate-pressure product from the rest condition. The T₂ sensitivity is approximately 95% higher with the new T₂ method than turbo-spin-echo method.

The CMR oxygenation method demonstrates the potential for non-invasive estimation of myocardial oxygenation, and should be explored in patients with altered myocardial oxygenation.