Proton decoupling and nuclear Overhauser effect (NOE) enhancement significantly improve the signal-to-noise ratio and enhance resolution of metabolites in in vivo P-31 MRS, We obtained proton-decoupled, NOE-enhanced, phospholipid-saturated P-31 spectra localized to defined regions within the normal liver using three-dimensional chemical shift imaging, Proton-decoupling resulted in the resolution of two major peaks in the phosphomonoester (PME) region, three peaks in the phosphodiester (PDE) region and a diphosphodiester peak, In order to obtain molar quantitation, we measured the NOE of all hepatic phosphorus resonances, and we corrected for saturation effects by measuring hepatic metabolite T-1 using the variable nutation angle method with phase-cycled, B-1-independent rotation, adiabatic pulses, After corrections for saturation effects, NOE enhancement, B, variations and point spread effects, the following mean concentrations (mmol/l of liver) (+/-SD) were obtained: [PME(1)]=1.2+/-0.4, [PME(2)+2,3-DPG]=1.1+/-0.1, [Pi+2,3-DPG]=2.8+/-0.5, [GPEth]=2.8+/-0.7, [GPChol]=3.5+/-0.6 and [beta-NTP]=3.8+/-0.3. T-1 and NOE enhancement were strongly correlated (r=90), and indicated that the fractional contribution of H-1-P-31 dipolar relaxation to total P-31 relaxation is minimal for NTPs, moderate for PMEs and high for PDEs in liver Proton-decoupling and NOE enhancement permit one to obtain more information about in vivo metabolism of liver than previously available and should enhance the utility of P-31 MRS for the study of hepatic disorders.
