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 P_i 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.