Spatially localized 1H NMR spectra of metabolites in the human brain.

Abstract

Using a surface coil, we have obtained 'H NMR spectra from metabolites in the human brain. Localization was achieved by combining depth pulses with imageselected in vivo spectroscopy magnetic field gradient methods.'H spectra in which total creatine (3.03 ppm) has a signal/noise ratio of 95:1 were obtained in 4 min from 14 ml of brain. A resonance at 2.02 ppm consisting predominantly of Nacetylaspartate was measured relative to the creatine peak in gray and white matter, and the ratio was lower in the white matter. The spin-spin relaxation times of N-acetylaspartate and creatine were measured in white and gray matter and while creatine relaxation times were the same in both, the N-acetylaspartate relaxation time was longer in white matter.Lactate was detected in the normoxic brain and the average of three measurements was =0.5 mM from comparison with the creatine plus phosphocreatine peak, which was assumed to be 10.5 mM.The ability of in vivo 1H NMR to measure concentrations of compounds noninvasively has been used to study brain metabolism in animals during hypoxia, hypoglycemia, and ischemia as well as under normal conditions (1-4). The recent development of human-sized magnets with fields up to 2.1 T along with techniques for obtaining spectra from localized volumes has made it possible to obtain 'H NMR brain spectra from humans (5, 6). While human brain spectra have been obtained with coils surrounding the entire head (6), their sensitivity and spectral resolution have been low compared to animal studies. In this communication, we show 'H NMR spectra of the human brain at 2.1 T with spectral resolution and sensitivity comparable to that achieved in animals at 8.5 T. High signal/noise spectra have been obtained in 4 min from 3 x 3 x 1.5 cm volumes. This degree of spatial localization, obtained by using a surface coil with a hybrid three-dimensional image-selected in vivo spectroscopy (ISIS)/depth pulse technique, has allowed us to make regional studies of human brain metabolites. The peak at 2.02 ppm that came from N-acetylaspartate with contributions from overlapping resonances (0. A. C. Petroff, personal communication) was consistently lower in white matter than in gray matter, relative to the total creatine peak (the term total creatine is used in this paper to refer to creatine plus phosphocreatine). This showed the ability of the present technique to measure spatial variations of chemical concentrations. We shall describe the peak at 2.02 ppm as N-acetylaspartate throughout this paper, keeping in mind that there are very probably appreciable contributions to its intensity from other resonances. We have previously shown that the C3 protons of glutamate and y-aminobutyrate overlap this peak. In addition, it has been pointed out to us (E. Berman, personal communication) that the N-acetyl peaks of several compounds, including sialic acid, are observed at 2.02 ppm and might be contributing to the observed intensity. The lactate methyl resonance at 1.33 ppm was resolved and positively identified by ...

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