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. 18 F-fluorodeoxyglucose (18 F-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 (FI O2  = .209) and hypoxic gas (FI O2  = .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.