Simultaneous determination of dynamic cardiac metabolism and function using PET/MRI

Background: Cardiac metabolic changes in heart disease precede overt contractile dysfunction. However, metabolism and function are not typically assessed together in clinical practice. The purpose of this study was to develop a cardiac positron emission tomography/magnetic resonance (PET/MR) stress test to assess the dynamic relationship between contractile function and metabolism in a preclinical model. Methods: Following an overnight fast, healthy pigs (45-50 kg) were anesthetized and mechanically ventilated. ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) solution was administered intravenously at a constant rate of 0.01 mL/s for 60 minutes. A cardiac PET/MR stress test was performed using normoxic gas (F_IO₂ =.209) and hypoxic gas (F_IO₂ =.12). Simultaneous cardiac imaging was performed on an integrated 3T PET/MR scanner. Results: Hypoxic stress induced a significant increase in heart rate, cardiac output, left ventricular (LV) ejection fraction (EF), and peak torsion. There was a significant decline in arterial SpO₂, LV end-diastolic and end-systolic volumes in hypoxia. Increased LV systolic function was coupled with an increase in myocardial FDG uptake (Ki) during hypoxic stress. Conclusion: PET/MR with continuous FDG infusion captures dynamic changes in both cardiac metabolism and contractile function. This technique warrants evaluation in human cardiac disease for assessment of subtle functional and metabolic abnormalities.