Measurement of glycine in healthy and tumorous brain by triple‐refocusing MRS at 3 T in vivo |
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| Authors: | Vivek Tiwari Zhongxu An Sandeep K. Ganji Jeannie Baxter Toral R. Patel Edward Pan Bruce E. Mickey Elizabeth A. Maher Marco C. Pinho Changho Choi |
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| Affiliation: | 1. Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, USA;2. Department of Neurology and Neurotherapeutics, University of Texas Southwestern Medical Center, Dallas, TX, USA;3. Department of Neurological Surgery, University of Texas Southwestern Medical Center, Dallas, TX, USA;4. Harold C. Simmons Cancer Center, University of Texas Southwestern Medical Center, Dallas, TX, USA;5. Annette Strauss Center for Neuro‐Oncology, University of Texas Southwestern Medical Center, Dallas, TX, USA;6. Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA;7. Department of Radiology, University of Texas Southwestern Medical Center, Dallas, TX, USA |
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| Abstract: | Glycine (Gly) has been implicated in several neurological disorders, including malignant brain tumors. The precise measurement of Gly is challenging largely as a result of the spectral overlap with myo‐inositol (mI). We report a new triple‐refocusing sequence for the reliable co‐detection of Gly and mI at 3 T and for the evaluation of Gly in healthy and tumorous brain. The sequence parameters were optimized with density‐matrix simulations and phantom validation. With a total TE of 134 ms, the sequence gave complete suppression of the mI signal between 3.5 and 3.6 ppm and, consequently, well‐defined Gly (3.55 ppm) and mI (3.64 ppm) peaks. In vivo 1H magnetic resonance spectroscopy (MRS) data were acquired from the gray matter (GM)‐dominant medial occipital and white matter (WM)‐dominant left parietal regions in six healthy subjects, and analyzed with LCModel using in‐house‐calculated basis spectra. Tissue segmentation was performed to obtain the GM and WM contents within the MRS voxels. Metabolites were quantified with reference to GM‐rich medial occipital total creatine at 8 mM. The Gly and mI concentrations were estimated to be 0.63 ± 0.05 and 8.6 ± 0.6 mM for the medial occipital and 0.34 ± 0.05 and 5.3 ± 0.8 mM for the left parietal regions, respectively. From linear regression of the metabolite estimates versus fractional GM content, the concentration ratios between pure GM and pure WM were estimated to be 2.6 and 2.1 for Gly and mI, respectively. Clinical application of the optimized sequence was performed in four subjects with brain tumor. The Gly levels in tumors were higher than those of healthy brain. Gly elevation was more extensive in a post‐contrast enhancing region than in a non‐enhancing region. The data indicate that the optimized triple‐refocusing sequence may provide reliable co‐detection of Gly and mI, and alterations of Gly in brain tumors can be precisely evaluated. |
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| Keywords: | 1H MRS 3 T glioma glycine (Gly) gray matter human brain triple refocusing white matter |
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