Glycine MRS Imaging at 3T

Recent studies indicate abnormal Gly levels in a wide range of brain tumor subtypes including gliomas, as well as a variety of cancer cell lines. Thus Gly may be a biomarker for primary as well as metastatic brain tumors. Given the cellular heterogeneity as well as regional variations in metabolic alterations in brain tumors, imaging of Gly may have important clinical application in the management of patients with brain tumors.

In vivo detection of Gly using 1H MRS in the human brain is challenging primarily due to the presence of the overlapping multiplet of myo-inositol (mIns), whose concentration is much higher (5-fold to 7-fold) than the Gly concentration in normal physiological conditions. Extensive suppression of the mIns multiplet in the proximity of the Gly resonance (3.55 ppm) is essential for reliable detection of Gly. 1H MRS imaging of Gly in the human brain has been developed at 3T based on our previously-reported single-voxel MRS scheme.

1H MRS imaging data from a subject with multi-focal glioblastoma. Spectra from tumors (A and C) and from the corresponding contralateral locations (B and D) are shown with spectral analysis resutls.

Following the validation in a phantom solution, we tested the feasibility of the Gly spectroscopic imaging method in both healthy subjects and subjects with brain tumors. Spectral fitting was used to resolve the Gly signal from the neighboring metabolite signals. Analysis of the MRS data showed that the Gly elevation is significantly higher in grade IV gliomas than in grade II and grade III tumors.

Brain scans
Spectral analysis results from the same subject. Concentrations of Gly and mIns were estimated with reference to the mean tCr estimate within a black box in the T2w-FLAIR iamge and 6.4 mM.