Mapping of intracellular pH in the in vivo rodent heart using hyperpolarized [1-13C]pyruvate


Purpose: To demonstrate the feasibility of mapping intracellular pH within the in vivo rodent heart. Alterations in cardiac acid-base balance can lead to acute contractile depression and alterations in Ca2+ signaling. The transient reduction in adenosine triphosphate (ATP) consumption and cardiac contractility may be initially beneficial; however, sustained pH changes can be maladaptive, leading to myocardial damage and electrical arrhythmias. Methods: Spectrally selective radiofrequency (RF) pulses were used to excite the math formula and CO2 resonances individually while preserving signal from the injected hyperpolarized [1-13C]pyruvate. The large flip angle pulses were placed within a three-dimensional (3D) imaging acquisition, which exploited CA-mediated label exchange between math formula and CO2. Images at 4.5 × 4.5 × 5 mm3 resolution were obtained in the in vivo rodent heart. The technique was evaluated in healthy rodents scanned at baseline and during high cardiac workload induced by dobutamine infusion. Results: The intracellular pH was measured to be 7.15 ± 0.04 at baseline, and decreased to 6.90 ± 0.06 following 15 min of continuous β-adrenergic stimulation. Conclusions: Volumetric maps of intracellular pH can be obtained following an injection of hyperpolarized [1-13C]pyruvate. The new method is anticipated to enable assessment of stress-inducible ischemia and potential ventricular arrythmogenic substrates within the ischemic heart

In Magnetic Resonance in Medicine