Cardiac 17O MRI: toward direct quantification of myocardial oxygen consumption.

A new (17)O-labeled blood contrast agent was injected intravenously in control dogs. Electrocardiogram (ECG)-triggered myocardial T(1)rho imaging was performed to obtain spin-locking T(1)rho-weighted myocardial signals for the detection of resultant metabolite H(2) (17)O water in the heart. Bolus and slow injection methods of various doses of the (17)O-labeled and (16)O-labeled agents were carried out in order to evaluate the sensitivity of this method and determine the optimal injection method. Bolus injection provided approximately 1% signal reduction, whereas slow injection with larger amount of agent yielded 11.9 +/- 0.6% signal reduction. Myocardial oxygen consumption rate was determined by a technique to quantify cerebral oxygenation consumption rate previously developed in (17)O brain studies. With either injection method, myocardial oxygen consumption rate at rest was 5.0 - 5.6 micromol/g/min. Therefore, it appears feasible to detect metabolically generated H(2) (17)O water in vivo in the heart, using the (17)O-labeled blood tracer. Myocardial oxygen consumption rate can then be quantified in vivo, which may open new doors for the assessment of myocardial metabolism.