在功能性磁共振波谱实验中,使用MEGA-PRESS研究视觉刺激背后的NAA和NAAG动力学。

Investigation of NAA and NAAG dynamics underlying visual stimulation using MEGA-PRESS in a functional MRS experiment.

作者信息

Landim Ricardo C G, Edden Richard A E, Foerster Bernd, Li Li Min, Covolan Roberto J M, Castellano Gabriela

机构信息

Neurophysics Group, Cosmic Rays and Chronology Department, Institute of Physics Gleb Wataghin, University of Campinas - UNICAMP, Brazil; CInAPCe Program (Cooperação Interinstitucional de Apoio a Pesquisas sobre o Cérebro), São Paulo State, Brazil.

Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, United States; F. M. Kirby Center for Functional MRI, Kennedy Krieger Institute, Baltimore, MD, UK.

出版信息

Magn Reson Imaging. 2016 Apr;34(3):239-45. doi: 10.1016/j.mri.2015.10.038. Epub 2015 Dec 2.

Abstract

N-acetyl-aspartate (NAA) is responsible for the majority of the most prominent peak in (1)H-MR spectra, and has been used as diagnostic marker for several pathologies. However, ~10% of this peak can be attributed to N-acetyl-aspartyl-glutamate (NAAG), a neuropeptide whose release may be triggered by intense neuronal activation. Separate measurement of NAA and NAAG using MRS is difficult due to large superposition of their spectra. Specifically, in functional MRS (fMRS) experiments, most work has evaluated the sum NAA+NAAG, which does not appear to change during experiments. The aim of this work was to design and perform an fMRS experiment using visual stimulation and a spectral editing sequence, MEGA-PRESS, to further evaluate the individual dynamics of NAA and NAAG during brain activation. The functional paradigm used consisted of three blocks, starting with a rest (baseline) block of 320 s, followed by a stimulus block (640 s) and a rest block (640 s). Twenty healthy subjects participated in this study. On average, subjects followed a pattern of NAA decrease and NAAG increase during stimulation, with a tendency to return to basal levels at the end of the paradigm, with a peak NAA decrease of -(21±19)% and a peak NAAG increase of (64±62)% (Wilcoxon test, p<0.05). These results may relate to: 1) the only known NAAG synthesis pathway is from NAA and glutamate; 2) a relationship between NAAG and the BOLD response.

摘要

N-乙酰天门冬氨酸(NAA)是氢质子磁共振波谱(¹H-MR spectra)中最显著峰的主要成分,已被用作多种疾病的诊断标志物。然而,该峰的约10%可归因于N-乙酰天门冬氨酰谷氨酸(NAAG),这是一种神经肽,其释放可能由强烈的神经元激活触发。由于NAA和NAAG的波谱大量重叠,使用磁共振波谱法(MRS)单独测量它们很困难。具体而言,在功能磁共振波谱(fMRS)实验中,大多数研究评估的是NAA + NAAG的总和,而这在实验过程中似乎没有变化。本研究的目的是设计并进行一项fMRS实验,利用视觉刺激和一种频谱编辑序列MEGA-PRESS,进一步评估大脑激活过程中NAA和NAAG的个体动态变化。所使用的功能范式包括三个阶段,首先是320秒的静息(基线)阶段,接着是640秒的刺激阶段和640秒的静息阶段。20名健康受试者参与了本研究。平均而言,受试者在刺激过程中呈现出NAA减少和NAAG增加的模式,在范式结束时倾向于恢复到基础水平,NAA的最大减少幅度为-(21±19)%,NAAG的最大增加幅度为(64±62)%(Wilcoxon检验,p<0.05)。这些结果可能与以下因素有关:1)唯一已知的NAAG合成途径是由NAA和谷氨酸合成;2)NAAG与血氧水平依赖性功能磁共振成像(BOLD)反应之间的关系。

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