GABA+和Glx(谷氨酸和谷氨酰胺)是广泛研究的代谢产物,然而,常用的磁共振波谱(MRS)技术有很大的局限性,包括对B0和B1+不均匀性的敏感性,MEGA脉冲的有限带宽,在7T处突出的高SAR。为了解决这些限制,我们提出了SLOW-EPSI方法,采用大的3DMRSI覆盖和实现高分辨率低至0.26毫升。模拟结果表明,在[-0.3,+0.3]ppm和[40%]的范围内,GABA和Glx的SLOW编辑对B0和B1不均匀性的鲁棒性。250%],分别。两个协议,两者都使用70毫米厚的FOV板,被用来瞄准体内不同的大脑区域,通过它们的方向来区分:横向和倾斜。方案1(n=11)包含5个位置(皮质灰质,白质,额叶,顶叶,和扣带回)。方案2(n=5)涉及9个位置(皮质灰质,白质,额叶,枕叶,扣带回,尾状核,海马体,壳核,和下丘脑)。以逐步方式进行GABA+和Glx的定量分析。首先,使用水参考数据校正B1/B1不均匀性。接下来,采用光谱拟合计算GABA+和Glx值。最后,将每个选定区域的GABA+水平与同一受试者内的全局Glx进行比较,生成GABA+/Glx_global比率。我们从两个方案的发现表明,皮质灰质中的GABA/Glx_global水平比白质高约16%。在特定区域如尾状核(0.118±0.067)观察到方案2获得的GABA+/Glx_global水平升高,壳核(0.108±0.023),丘脑(0.092±0.036),枕骨皮质(0.091±0.010),与皮质灰质相比(0.079±0.012)。总的来说,我们的结果强调了SLOW-EPSI作为一种稳健有效的技术在7T时精确测量GABA+和Glx的有效性.与以前的基于SVS和2D-MRSI的编辑序列相比,只有一个或有限数量的大脑区域可以同时测量,这里介绍的方法从任何大脑区域和任何可以在检查后灵活选择的任意形状的体积测量GABA+和Glx。通过光谱拟合对多个大脑区域的GABA+和Glx的定量可通过9分钟的采集来实现。此外,需要18-27分钟(GABA+)和9-18分钟(Glx)的采集时间来生成3D地图,使用高斯拟合和峰值积分构造。
GABA+ and Glx (glutamate and glutamine) are widely studied metabolites, yet the commonly used magnetic resonance spectroscopy (MRS) techniques have significant limitations, including sensitivity to B0 and B1+-inhomogeneities, limited bandwidth of MEGA-pulses, high SAR which is accentuated at 7T. To address these limitations, we propose
SLOW-EPSI method, employing a large 3D MRSI coverage and achieving a high resolution down to 0.26 ml. Simulation results demonstrate the robustness of
SLOW-editing for both GABA+ and Glx against B0 and B1+-inhomogeneities within the range of [-0.3, +0.3] ppm and [40 %, 250 %], respectively. Two protocols, both utilizing a 70 mm thick FOV slab, were employed to target distinct brain regions in vivo, differentiated by their orientation: transverse and tilted. Protocol 1 (n = 11) encompassed 5 locations (cortical gray matter, white matter, frontal lobe, parietal lobe, and cingulate gyrus). Protocol 2 (n = 5) involved 9 locations (cortical gray matter, white matter, frontal lobe, occipital lobe, cingulate gyrus, caudate nucleus, hippocampus, putamen, and inferior thalamus). Quantitative analysis of GABA+ and Glx was conducted in a stepwise manner. First, B1+/B1--inhomogeneities were corrected using water reference data. Next, GABA+ and Glx values were calculated employing spectral fitting. Finally, the GABA+ level for each selected region was compared to the global Glx within the same subject, generating the GABA+/Glx_global ratio. Our findings from two protocols indicate that the GABA+/Glx_global level in cortical gray matter was approximately 16 % higher than in white matter. Elevated GABA+/Glx_global levels acquired with protocol 2 were observed in specific regions such as the caudate nucleus (0.118±0.067), putamen (0.108±0.023), thalamus (0.092±0.036), and occipital cortex (0.091±0.010), when compared to the cortical gray matter (0.079±0.012). Overall, our results highlight the effectiveness of
SLOW-EPSI as a robust and efficient technique for accurate measurements of GABA+ and Glx at 7T. In contrast to previous SVS and 2D-MRSI based editing sequences with which only one or a limited number of brain regions can be measured simultaneously, the method presented here measures GABA+ and Glx from any brain area and any arbitrarily shaped volume that can be flexibly selected after the examination. Quantification of GABA+ and Glx across multiple brain regions through spectral fitting is achievable with a 9-minute acquisition. Additionally, acquisition times of 18-27 min (GABA+) and 9-18 min (Glx) are required to generate 3D maps, which are constructed using Gaussian fitting and peak integration.