Bogner Wolfgang, Gagoski Borjan, Hess Aaron T, Bhat Himanshu, Tisdall M Dylan, van der Kouwe Andre J W, Strasser Bernhard, Marjańska Małgorzata, Trattnig Siegfried, Grant Ellen, Rosen Bruce, Andronesi Ovidiu C
Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA; MRCE, Department of Biomedical Imaging and Image-guided Therapy, Medical University Vienna, Vienna, Austria.
Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA.
Neuroimage. 2014 Dec;103:290-302. doi: 10.1016/j.neuroimage.2014.09.032. Epub 2014 Sep 26.
Gamma-aminobutyric acid (GABA) and glutamate (Glu) are the major neurotransmitters in the brain. They are crucial for the functioning of healthy brain and their alteration is a major mechanism in the pathophysiology of many neuro-psychiatric disorders. Magnetic resonance spectroscopy (MRS) is the only way to measure GABA and Glu non-invasively in vivo. GABA detection is particularly challenging and requires special MRS techniques. The most popular is MEscher-GArwood (MEGA) difference editing with single-voxel Point RESolved Spectroscopy (PRESS) localization. This technique has three major limitations: a) MEGA editing is a subtraction technique, hence is very sensitive to scanner instabilities and motion artifacts. b) PRESS is prone to localization errors at high fields (≥3T) that compromise accurate quantification. c) Single-voxel spectroscopy can (similar to a biopsy) only probe steady GABA and Glu levels in a single location at a time. To mitigate these problems, we implemented a 3D MEGA-editing MRS imaging sequence with the following three features: a) Real-time motion correction, dynamic shim updates, and selective reacquisition to eliminate subtraction artifacts due to scanner instabilities and subject motion. b) Localization by Adiabatic SElective Refocusing (LASER) to improve the localization accuracy and signal-to-noise ratio. c) K-space encoding via a weighted stack of spirals provides 3D metabolic mapping with flexible scan times. Simulations, phantom and in vivo experiments prove that our MEGA-LASER sequence enables 3D mapping of GABA+ and Glx (Glutamate+Gluatmine), by providing 1.66 times larger signal for the 3.02ppm multiplet of GABA+ compared to MEGA-PRESS, leading to clinically feasible scan times for 3D brain imaging. Hence, our sequence allows accurate and robust 3D-mapping of brain GABA+ and Glx levels to be performed at clinical 3T MR scanners for use in neuroscience and clinical applications.
γ-氨基丁酸（GABA）和谷氨酸（Glu）是大脑中的主要神经递质。它们对健康大脑的功能至关重要，其改变是许多神经精神疾病病理生理学的主要机制。磁共振波谱（MRS）是体内无创测量GABA和Glu的唯一方法。GABA检测特别具有挑战性，需要特殊的MRS技术。最常用的是采用单体素点分辨波谱（PRESS）定位的Mescher-Garwood（MEGA）差异编辑技术。该技术有三个主要局限性：a）MEGA编辑是一种减法技术，因此对扫描仪不稳定性和运动伪影非常敏感。b）PRESS在高场（≥3T）时容易出现定位误差，这会影响准确量化。c）单体素波谱（类似于活检）一次只能探测单个位置的稳定GABA和Glu水平。为了缓解这些问题，我们实施了一种具有以下三个特点的3D MEGA编辑MRS成像序列：a）实时运动校正、动态匀场更新和选择性重新采集，以消除由于扫描仪不稳定性和受试者运动引起的减法伪影。b）通过绝热选择性重聚焦（LASER）进行定位，以提高定位准确性和信噪比。c）通过加权螺旋堆栈进行K空间编码，提供具有灵活扫描时间的3D代谢图谱。模拟、体模和体内实验证明，我们的MEGA-LASER序列能够实现GABA+和Glx（谷氨酸+谷氨酰胺）的3D映射，与MEGA-PRESS相比，为GABA+的3.02ppm多重峰提供了1.66倍更大的信号，从而实现了临床可行的3D脑成像扫描时间。因此，我们的序列允许在临床3T MR扫描仪上准确且稳健地进行脑GABA+和Glx水平的3D映射，用于神经科学和临床应用。
