Absolute quantitative proton NMR spectroscopy based on the amplitude of the local water suppression pulse. Quantification of brain water and metabolites

Quantification in localized proton NMR spectroscopy has been achieved by various methods in recent years. A new method for absolute quantification is described in this paper. The method simultaneously rules out problems with B1 field inhomogeneity and coil loading, utilizing a relation between the locally optimized amplitude of a chemical shift selective water suppression pulse and the acquired signal. Validity and feasibility of quantification using the method of the water suppression pulse is demonstrated. Brain water and cerebral metabolites have been quantified in a study of 12 healthy volunteers. Localized proton NMR spectra were obtained from a region of primarily white matter in the occipital lobe. The observable water content in the NMR spectra was 0.685 +/- 0.025. The absolute metabolite concentrations were: [total choline] = 1.25 +/- 0.21 nM, [total creatine] = 6.71 +/- 0.59 nM and [NAA] = 9.15 +/- 0.74 nM. It is concluded that the quantification method is easily applied in vivo, and that the absolute concentrations obtained are similar to results in other studies except those relying on assumptions of the concentration of an internal reference. The advantage of the quantification method reported here is that it is independent of the assumptions needed for other methods.