Measurement of glycine in human brain by triple refocusing ¹H-MRS in vivo at 3.0T

A new ¹H-MRS filtering strategy for selective measurement of glycine (Gly) in human brain in vivo at 3.0T is proposed. Investigation of multiple refocusing following a 90° excitation pulse indicated that triple refocusing is most effective for suppression of the strongly coupled resonances of myo-inositol (ml) at the Gly 3.55-ppm resonance. The echo times of the triple refocusing were optimized, with numerical analysis of the filtering performance, as {TE₁, TE₂, TE₃} = {67, 62, 69} ms. Compared with the 90°-acquired ml signal the ml suppression ratios of the filter were 170 and 1000, in terms of peak amplitude and area, respectively, between 3.51 and 3.59 ppm. From LCModel analyses, using density-matrix calculated spectra as basis functions, the concentration of Gly in parieto-occipital cortex of healthy adults was estimated to be 0.5 ± 0.1 mM (mean ± SD, n = 6), with reference to creatine at 8 mM.