31P NMR measurements of myocardial pH in vivo.

A 31P NMR magnetization transfer method for measuring myocardial pH in vivo is demonstrated in the lamb, dog and cat. The method involves measuring the difference in chemical shift between the resonances of phosphocreatine and inorganic phosphate in magnetization transfer difference spectra in which the gamma-phosphate resonance of ATP has been saturated. The method has been verified by measuring the chemical shift difference between the resonances of 2-deoxyglucose 6-phosphate and phosphocreatine following infusion of the animals with 2-deoxyglucose. The measured pH values are significantly lower than those obtained in previous studies on the heart in vivo.