Broadband proton decoupling in human 31p NMR spectroscopy

Abstract

The limited chemical shift dispersion of in vivo 31P NMR spectra obtained at the relatively low field strengths used for human applications is the cause of poor spectral resolution. This makes it difficult to obtain accurate quantitative information from overlapping resonances, and interesting resonances may be obscured. At 1.5 T unresolved 1H-31P couplings contribute significantly to the linewidth of in vivo 31P NMR resonances. Therefore, proton decoupling can improve spectral resolution substantially, resulting in better resolved resonances and more reliable quantitative information. In this work it is shown that well resolved resonances of glycerophosphocholine, glycerophosphoethanolamine and phosphoethanolamine are obtained in 1H decoupled 31P NMR spectra of human muscle, brain, and liver. In spectra of the human heart it has been possible to resolve the myocardial Pi signal from the signals of 2,3-diphosphoglycerate from blood. With surface coils it is difficult to achieve broadband decoupling over the entire sensitive region of the coil by using conventional decoupling sequences. This problem has been overcome by applying a train of frequency modulated inversion pulses to achieve proper decoupling despite B2 inhomogeneity. Broadband 1H decoupling of 31P NMR spectra was possible without exceeding specific absorption rate guidelines.