In vivo detection of brain glycine with echo-time-averaged 1H magnetic resonance spectroscopy at 4.0 T

Abstract

A single-voxel proton magnetic resonance spectroscopy (1H-MRS) method is described that enables the in vivo measurement of endogenous brain glycine (Gly) levels in human subjects. At 4.0 T, TE-averaging 1H-MRS dramatically attenuates the overlapping myo-inositol (ml) resonances at 3.52 ppm, permitting a more reliable measure of the Gly singlet peak. This methodology initially is described and tested in phantoms. The phantom data infers that the 3.55-ppm peak predominantly is Gly with a smaller contribution from ml. The composite resonance thus is differentiated from pure Gly and ml and is labeled Gly*. The ml contribution was calculated as <2% of the total Gly* signal for a 1:1 ml/Gly mixture. The technique subsequently was used to acquire TE-averaged 1H-MRS data from the occipital cortex of healthy control subjects. The resultant spectra closely resembled experimental phantom data. LC-model analysis provided a means for quantifying TE-averaged 1H-MRS spectra and a mean test-retest variability measure of 15% was established for brain Gly* levels in studies of six healthy subjects. © 2006 Wiley-Liss, Inc.