Abstract Body (Do not enter title and authors here): Background
Myocardial oxygen consumption (MVO₂) is a central marker in measuring cardiac energetics. Current methods to quantify MVO₂ are inaccessible due to the requirement of invasive procedures or PET agents that require onsite cyclotrons.
Hypothesis
A free-breathing, non-ECG-gated, motion-resolved Cardiac MR blood oximetry technique can noninvasively quantify MVO₂ in standard clinical MRI scanners without using ionizing radiation and contrast agents.
Method
The developed free-breathing CMR imaging technique was prescribed in a 3T clinical scanner to the mid left ventricle (LV) and the cross-section of the coronary sinus(CS) slices of the heart to obtain the corresponding blood oxygenation (SbO₂) and the hematocrit (Hct) in heart chambers. 2D phase contrast CMR was performed in the CS to quantify the myocardial blood flow (MBF). The MVO₂ was quantified with Fick’s law (MVO₂=arterio-venous oxygen difference x MBF). We examined the developed method in healthy pigs (N=7) under rest and adenosine stress and validated it against invasive blood sampling. In addition, we tested the method’s clinical feasibility in healthy human volunteers (N=4).
Results
Comparable blood oxygenation levels (SbO₂) and MVO₂ were measured and compared between the non-invasive CMR and invasive ground truth (Fig. 1). Significantly increased coronary sinus SbO₂ is observed in both methods during adenosine infusion. It is accompanied by decreased MVO₂ and rate pressure product (RPP) (Rest: CMR=10.2±2.7ml/min, Inv.=10.8±6.9 ml/min, RPP=7956.9±620.9 mmHg/min; Stress: CMR=5.3±1.9 ml/min, Inv=6.3±3.6 ml/min, RPP=5338.2±618.3 mmHg/min). In Fig. 2, the healthy human volunteers' MVO₂ estimations(14.1±6.7ml/min) shows no statistical difference compared to the previous invasive measurements(16.5±4.8 ml/min, Ganz, et al. circulation 1971).
Conclusions
The proposed noninvasive CMR technique can quantify MVO₂ in standard MRI scanners without using a needle. It has the potential to provide an accessible, risk-free assessment of myocardial metabolism for patients with potential metabolism impairments.