Younis Samaira, Hougaard Anders, Christensen Casper E, Vestergaard Mark B, Petersen Esben T, Boer Vincent O, Paulson Olaf B, Ashina Messoud, Marsman Anouk, Larsson Henrik B W
Danish Headache Center, Department of Neurology, Rigshospitalet Glostrup, Faculty of Health and Medical Sciences, University of Copenhagen, Glostrup, Denmark.
Functional Imaging Unit, Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet Glostrup, Faculty of Health and Medical Sciences, University of Copenhagen, Glostrup, Denmark.
Front Neurosci. 2020 Oct 23;14:559314. doi: 10.3389/fnins.2020.559314. eCollection 2020.
Glutamate detection in pons and thalamus using proton magnetic resonance spectroscopy (H-MRS) after an intervention is of interest for studying various brain disorders. However, H-MRS in these brain regions is challenging and time-consuming, especially in longitudinal study designs. H-MRS of more cortical structures at the ultrahigh magnetic field strength of 7T yields an improved spectral output, including separation of the glutamate signal from the glutamine signal, in a shorter and more feasible scan time, as compared to conventional clinical field strengths. For this purpose, we compared the feasibility of H-MRS at 3T and 7T in pons and thalamus by applying a longitudinal study design of repeated measures on same day and three separate days at both field strength in five healthy participants. Total H-MRS acquisition time was reduced by a factor 3.75 for pons and by a factor 3 for thalamus at 7T as compared to 3T. We found higher spectral signal-to-noise ratio (SNR) ( < 0.001), lower linewidth ( = 0.001) and lower Cramér-Rao lower bounds (CRLB) ( < 0.001) for the combined glutamate and glutamine signal (Glx) in thalamus at 7T as compared to 3T. In pons, CRLB of Glx and SNR were lower at 7T ( = 0.002 and = 0.006), with no differences in linewidth compared to 3T. Mean within-subject variability of Glx concentration estimates was lower at 7T compared to 3T for both pons and thalamus. At 7T, it was possible to assess glutamate and γ-aminobutyric acid (GABA) simultaneously in pons and thalamus. In conclusion, H-MRS at 7T resulted in improved spectral quality while allowing shorter scan times than at 3T as well as estimation of the pure glutamate signal in pons and thalamus. This opens up the opportunity for multimodal study designs and multiregional subcortical H-MRS research. Glutamate and GABA measurement at 7T in pons and thalamus is advantageous for future investigations of excitatory-inhibitory mechanisms in brain disorders.
干预后使用质子磁共振波谱（H-MRS）检测脑桥和丘脑的谷氨酸，对于研究各种脑部疾病具有重要意义。然而，在这些脑区进行H-MRS具有挑战性且耗时，尤其是在纵向研究设计中。与传统临床场强相比，在7T超高磁场强度下对更多皮质结构进行H-MRS，可在更短且更可行的扫描时间内获得改进的光谱输出，包括将谷氨酸信号与谷氨酰胺信号分离。为此，我们通过对五名健康参与者在3T和7T场强下同一天和三个不同日期进行重复测量的纵向研究设计，比较了脑桥和丘脑在3T和7T时H-MRS的可行性。与3T相比，7T时脑桥的总H-MRS采集时间减少了3.75倍，丘脑减少了3倍。我们发现，与3T相比，7T时丘脑谷氨酸和谷氨酰胺联合信号（Glx）的光谱信噪比（SNR）更高（<0.001）、线宽更低（=0.001）以及克莱姆-拉奥下界（CRLB）更低（<0.001）。在脑桥中，7T时Glx的CRLB和SNR更低（=0.002和=0.006），与3T相比线宽无差异。脑桥和丘脑的Glx浓度估计的平均受试者内变异性在7T时比3T更低。在7T时，可以同时评估脑桥和丘脑中的谷氨酸和γ-氨基丁酸（GABA）。总之，7T时的H-MRS提高了光谱质量，同时允许比3T更短的扫描时间，并能估计脑桥和丘脑中的纯谷氨酸信号。这为多模态研究设计和多区域皮质下H-MRS研究提供了机会。在7T时测量脑桥和丘脑中的谷氨酸和GABA，有利于未来对脑部疾病中兴奋-抑制机制的研究。
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