1H MR spectroscopic imaging with short and long echo time to discriminate glycine in glial tumours

To investigate glycine (Gly) concentrations in low- and high-grade gliomas based on H-1 MR spectroscopic imaging (MRSI) with short and long echo time (TE). Myoinositol (MI) and Gly appear at the same resonance frequency of 3.56 ppm, but due to strong coupling the MI signal dephases more rapidly. Therefore, their contribution to the 3.56 ppm signal should be distinguishable comparing MRSI data acquired at short and long TE. H-1 MRSI (TE = 30 and 144 ms) was performed at 3 T in 29 patients with histopathological confirmed World Health Organization (WHO) grade II-IV gliomas and in FIVE healthy subjects. All spectra from the gliomas revealed increase of the 3.56 ppm resonance in the short TE spectra. Signal intensities of Gly and MI were differentiated either by analysing the short to long TE ratio of the resonance or by performing a weighted difference. Gly concentrations were compared between high-grade (WHO III-IV) and low-grade gliomas. High-grade gliomas showed significantly higher Gly concentrations compared to low-grade gliomas. Appropriate data processing of short and long TE H-1 MRSI provides a tool to distinguish and to quantify Gly and MI concentrations in gliomas. As Gly seems to be a marker of malignancy, more dedicated spectroscopic methods to differentiate these metabolites are justified.