Kinetics of the in vivo31P1H nuclear overhauser effect of the human-calf-muscle phosphocreatine resonance

In ³¹P¹H double-resonance experiments in a 1.5 T whole-body MR system, we observed in vivo the truncated driven, transient, and steady-state ³¹P-¹H nuclear Overhauser effect of the phosphocreatine resonance in ³¹P MR spectra of human gastrocnemius muscle. Maximum signal enhancements of 0.52 ± 0.01, 0.20 ± 0.01, and 0.79 ± 0.02 were measured, respectively. Fitting the data with theoretical functions which solve the multispin Solomon equations for N protons (S spins) dipolar coupled to a ³¹P nucleus (I spin) yields cross-relaxation times in the order of 20 s. In vivo experiments are feasible for studying relaxation mechanisms in coupled ³¹P¹H spin systems in intact tissue.