Continuous Imaging of the Cardiac Cycle Metabolism With Hyperpolarized [1-¹³C]Pyruvate

Hyperpolarized (HP) ¹³C MRI enables noninvasive assessment of myocardial metabolism. Current approaches typically acquire data only during diastole, ignoring phase-dependent metabolic changes. This study aimed to develop an imaging technique to capture HP [¹³C]bicarbonate production across both systole and diastole in healthy porcine hearts under rest and stress conditions. Six Danish domestic pigs underwent conventional cardiac MRI and HP [1-¹³C]pyruvate MRI on an MR750 3 T system (GE HealthCare) before and during pharmacological stress by injecting adenosine (250 μg/min/kg) and dobutamine (5 μg/min/kg). Metabolic imaging was obtained by single-frequency imaging on [¹³C]bicarbonate. Concurrent off-resonance excitation on [1-¹³C]pyruvate was utilized to generate a simultaneous pyruvate input function. Bicarbonate-to-pyruvate ratios (Bic/Pyr ratio) were compared from rest to stress throughout the cardiac cycle. Dynamic metabolic changes were successfully captured with sufficient temporal resolution to resolve both systolic and diastolic phases. From rest to stress, during systole the Bic/Pyr ratio increased by 150% (95% CI 50%-330%, p = 0.0076) and during diastole it increased by 170% (95% CI 50%-380%, p = 0.0083). During rest, the Bic/Pyr ratio decreased by 21% from systole to diastole (95% CI 4%-35%, p = 0.027), and during stress, it decreased by 16% (95% CI 4%-26%, p = 0.019). Simultaneous phase-resolved imaging of [1-¹³C]pyruvate and [¹³C]bicarbonate enables high-temporal-resolution assessment of myocardial metabolism during both systole and diastole compared to conventional single-frequency acquisitions. This simultaneous acquisition strategy removes the need for separate pyruvate and bicarbonate acquisitions, doubling the temporal resolution of the resulting image series, while revealing dynamic increases in Bic/Pyr ratio from rest to stress and between systole and diastole. This approach overcomes the limitations of single-phase imaging and provides a foundation for investigating phase-dependent metabolic alterations in disease.