Phosphorus-31 Magnetic Resonance Spectroscopy for Serial Measurements of Cardiac Energetics During...

Reliable organ preservation is critical to increasing donor availability and improving transplant outcomes. While static storage remains the standard for donor hearts, there is a need for precise methods to monitor myocardial energetics throughout preservation. Phosphorus-31 Magnetic Resonance Spectroscopy (³¹P MRS) enables direct, dynamic measurement of key energy metabolites, including Phosphocreatine (PCr), Adenosine TriPhosphate (ATP), inorganic phosphate (Pi), and intracellular pH. This technique allows for longitudinal, quantitative, and precise evaluation of myocardial metabolic status during ex vivo storage. Advantages of MRS include dynamic assessment of energy status and a global assessment of ventricular energy. The protocol begins with swine donor recovery, cardioplegia administration, and cardiectomy. The aortic arch is cut proximal to the brachiocephalic trunk to maximize the length of the ascending aorta. A ribbed cannula is secured into the distal ascending aorta, the left atrium is marked, and the heart is placed in a cylindrical, insulated container pre-filled with temperature-specific cardioplegia. The lid connects to the cannula, suspending the heart inside, and the container is sealed, maintaining a temperature within 1 °C for 1 h. The container is placed in a tailored Styrofoam box with an opening for a phosphorus tuned coil, aligning the coil center with the center of the left ventricle (LV). Scout images confirm LV placement near the ³¹P coil. B0 shimming ensures uniform excitation, followed by acquisition of a non-localized ³¹P MR spectrum. Post-processing identifies spectral peaks for calculating PCr/ATP, PCr/Pi ratios, and intracellular pH. In our protocol, ³¹P MRS is performed at serial timepoints between h 0 to 8. Between timepoints, the heart is stored in a standard storage device at the desired temperature. ³¹P MRS has allowed us to study time-dependent changes to energy depletion and the role of storage temperature in mitigating energy depletion over time.