Observation of metabolites in the human brain by MR spectroscopy.

Measurement of low molecular weight metabolites by hydrogen magnetic resonance (MR) spectroscopy is complicated by the presence of intense signals from water and lipids. A method of spatially resolved spectroscopy (SPARS), combined with techniques to suppress water signal, was used to overcome this problem. By means of SPARS, a signal can be obtained from a particular volume only, with no signal from the rest of the sample. Thus, a volume in the brain can be selected, and intense lipid signals from other tissue are suppressed. The SPARS technique is based on the use of pulsed magnetic field gradients, which makes it possible to select the sensitive volume on the basis of an MR image. Suppression of the intense water signal was achieved by applying a 1331 observation pulse. With these techniques, N-acetyl aspartate was successfully measured in the human brain with a 1.5-T whole-body imager, and lactate was observed in excised brain tissue of a pig. Measurement of low molecular weight metabolites has potential significance in evaluating patients with diseases of the brain; further studies are underway to assess this potential.