Dual-phase imaging of cardiac metabolism using hyperpolarized pyruvate

Purpose: Previous cardiac imaging studies using hyperpolarized (HP) [1-¹³C]pyruvate were acquired at end-diastole (ED). Little is known about the interaction between cardiac cycle and metabolite content in the myocardium. In this study, we compared images of HP pyruvate and products at end-systole (ES) and ED. Methods: A dual-phase ¹³C MRI sequence was implemented to acquire two sequential HP images within a single cardiac cycle at ES and ED during successive R-R intervals in an interleaved manner. Each healthy volunteer (N = 3) received two injections of HP [1-¹³C]pyruvate for the dual-phase imaging on the short-axis and the vertical long-axis planes. Spatial distribution of HP ¹³C metabolites at each cardiac phase was correlated to multiphase ¹H MRI to confirm the mechanical changes. Ratios of myocardial HP metabolites were compared between ES and ED. Segmental analysis was performed on the midcavity short-axis plane. Results: In addition to mechanical changes, metabolic profiles of the heart detected by HP [1-¹³C]pyruvate differed between ES and ED. The myocardial signal of [¹³C]bicarbonate relative to [1-¹³C]lactate was significantly smaller at ED than the ratio at ES (p <.05), particularly in mid-anterior and mid-inferoseptal segments. The distinct metabolic profiles in the myocardium likely reflect the technical aspects of the imaging approach such as the coronary flow in addition to the cyclical changes in metabolism. Conclusion: The study demonstrates that metabolic profiles of the heart, measured by HP [1-¹³C]pyruvate, are affected by the cardiac cycle in which that the data are acquired.