In vivo estimate of myocardial work and metabolic rate of FDG as a first step to the estimation of cardiac efficiency using hybrid PET/MRI technology

Objectives Hybrid PET/MRI technology offers the potential to make significant advances in the study of heart function relative to metabolite substrate utilization for patients in heart failure (HF). An imbalance between oxidative metabolism and cardiac function appears to be a key factor of disease progression in HF. Fatty acids (FAs) account for 50-70% of ATP production from FA β-oxidation in the normal adult myocardium as well as in frequently utilized animal models.

Methods Using hybrid PET/MRI technology, cardiac tissue efficiency is measured as the ratio of myocardial oxygen consumption (MVO2) [PET measures 11C-acetate kinetics as a surrogate for energy input] to cardiac tissue work [MRI measures tissue strain (distance) and finite element modeling estimates tissue stress (force)]. To evaluate the feasibility of our methodology, PET imaging data of 18FDG in the hearts of young normal rats were acquired simultaneously with the acquisition of tagged MRI at the University of Tübingen.

Results Comparison of the mid-ventricular estimates of cardiac work and 18FDG metabolic rate for each of the three rats showed negative correlations. The three rats had r2 values of -0.38, -0.54, and -0.50.

Conclusions These initial results showed that glucose metabolism was inversely related to the mechanical work of the heart for the three rats being studied suggesting that as the work increases other metabolic substrates, such as FAs, are preferred since they provide more energy per gram than glucose (9 vs. 4 kcal/gram). Our goal is to use hybrid PET/MRI to simultaneously calculate MVO2 and cardiac work and to relate the ratio (cardiac efficiency) to the metabolism of energetic substrates such as glucose and FAs.