Department of Psychological and Brain Sciences, Indiana University, Bloomington, Indiana, USA.
Program of Neuroscience, Indiana University, Bloomington, Indiana, USA.
NMR Biomed. 2021 Feb;34(2):e4453. doi: 10.1002/nbm.4453. Epub 2020 Dec 3.
Glutamate is an important neurotransmitter. Although many studies have measured glutamate concentration in vivo using magnetic resonance spectroscopy (MRS), researchers have not reached a consensus on the accuracy of glutamate quantification at the field strength of 3 T. Besides, there is not an optimal MRS protocol for glutamate measurement. In this work, both simulation and phantom scans indicate that glutamate can be estimated with reasonable accuracy (<10% error on average) using the standard Point-RESolved Spectroscopy (PRESS) technique with TE 30 ms; glutamine, however, is likely underestimated, which is also suggested by results from human scans using the same protocol. The phantom results show an underestimation of glutamate and glutamine for PRESS with long TE and MEGA-PRESS off-resonance spectra. Despite the underestimation, there is a high correlation between the measured values and the true values (r > 0.8). Our results suggest that the quantification of glutamate and glutamine is reliable but can be off by a scaling factor, depending on the imaging technique. The outputs from all three PRESS sequences (TE = 30, 68 and 80 ms) are also highly correlated with each other (r > 0.7) and moderately correlated (r > 0.5) with the results from the MEGA-PRESS difference spectra with moderate to good shimming (linewidth < 16 Hz).
谷氨酸是一种重要的神经递质。尽管许多研究已经使用磁共振波谱（MRS）在体内测量了谷氨酸浓度，但研究人员在 3T 场强下对谷氨酸定量的准确性尚未达成共识。此外，目前还没有用于测量谷氨酸的最佳 MRS 方案。在这项工作中，模拟和体模扫描均表明，使用标准的点分辨波谱（PRESS）技术（TE 为 30ms）可以以合理的精度（平均误差<10%）估计谷氨酸；然而，谷氨酸很可能被低估，这也被相同方案下的人体扫描结果所证实。体模结果显示，长 TE 的 PRESS 和 MEGA-PRESS 离频光谱会低估谷氨酸和谷氨酰胺。尽管存在低估，但测量值与真实值之间存在高度相关性（r>0.8）。我们的结果表明，谷氨酸和谷氨酰胺的定量是可靠的，但可能会因成像技术而存在比例因子误差。三种 PRESS 序列（TE=30、68 和 80ms）的输出彼此之间也高度相关（r>0.7），并且与适度至良好匀场（线宽<16Hz）的 MEGA-PRESS 差谱结果中度相关（r>0.5）。
