Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, Baltimore, MD, United States; F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States.
Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, Baltimore, MD, United States; F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States.
Neuroimage. 2019 Jan 15;185:181-190. doi: 10.1016/j.neuroimage.2018.10.002. Epub 2018 Oct 6.
To demonstrate the framework of a novel Hadamard-encoded spectral editing approach for simultaneously detecting multiple low-concentration brain metabolites in vivo at 3T.
HERCULES (Hadamard Editing Resolves Chemicals Using Linear-combination Estimation of Spectra) is a four-step Hadamard-encoded editing scheme. 20-ms editing pulses are applied at: (A) 4.58 and 1.9 ppm; (B) 4.18 and 1.9 ppm; (C) 4.58 ppm; and (D) 4.18 ppm. Edited signals from γ-aminobutyric acid (GABA), glutathione (GSH), ascorbate (Asc), N-acetylaspartate (NAA), N-acetylaspartylglutamate (NAAG), aspartate (Asp), lactate (Lac), and likely 2-hydroxyglutarate (2-HG) are separated with reduced signal overlap into distinct Hadamard combinations: (A+B+C+D); (A+B-C-D); and (A-B+C-D). HERCULES uses a novel multiplexed linear-combination modeling approach, fitting all three Hadamard combinations at the same time, maximizing the amount of information used for model parameter estimation, in order to quantify the levels of these compounds. Fitting also allows estimation of the levels of total choline (tCho), myo-inositol (Ins), glutamate (Glu), and glutamine (Gln). Quantitative HERCULES results were compared between two grey- and white-matter-rich brain regions (11 min acquisition time each) in 10 healthy volunteers. Coefficients of variation (CV) of quantified measurements from the HERCULES fitting approach were compared against those from a single-spectrum fitting approach, and against estimates from short-TE PRESS data.
HERCULES successfully segregates overlapping resonances into separate Hadamard combinations, allowing for the estimation of levels of seven coupled metabolites that would usually require a single 11-min editing experiment each. Metabolite levels and CVs agree well with published values. CVs of quantified measurements from the multiplexed HERCULES fitting approach outperform single-spectrum fitting and short-TE PRESS for most of the edited metabolites, performing only slightly to moderately worse than the fitting method that gives the lowest CVs for tCho, NAA, NAAG, and Asp.
HERCULES is a new experimental approach with the potential for simultaneous editing and multiplexed fitting of up to seven coupled low-concentration and six high-concentration metabolites within a single 11-min acquisition at 3T.
展示一种新的基于 Hadamard 编码的谱编辑方法的框架，用于在 3T 下同时检测体内多个低浓度脑代谢物。
HERCULES（Hadamard 编辑通过对谱线的线性组合估计来分辨化学物质）是一个四步 Hadamard 编码编辑方案。20 毫秒的编辑脉冲施加于：（A）4.58ppm 和 1.9ppm；（B）4.18ppm 和 1.9ppm；（C）4.58ppm；和（D）4.18ppm。γ-氨基丁酸（GABA）、谷胱甘肽（GSH）、抗坏血酸（Asc）、N-乙酰天冬氨酸（NAA）、N-乙酰天门冬氨酸谷氨酸（NAAG）、天冬氨酸（Asp）、乳酸（Lac）和可能的 2-羟戊二酸（2-HG）的编辑信号通过减少信号重叠成独特的 Hadamard 组合进行分离：（A+B+C+D）；（A+B-C-D）；和（A-B+C-D）。HERCULES 使用一种新的多路复用线性组合建模方法，同时拟合所有三个 Hadamard 组合，最大限度地利用模型参数估计的信息量，以量化这些化合物的水平。拟合还允许估计总胆碱（tCho）、肌醇（Ins）、谷氨酸（Glu）和谷氨酰胺（Gln）的水平。在 10 名健康志愿者的两个灰质和白质丰富的脑区（每个采集时间 11 分钟）之间比较了 HERCULES 定量结果。比较了 HERCULES 拟合方法与单谱拟合方法以及短 TE PRESS 数据的定量测量的变异系数（CV）。
HERCULES 成功地将重叠共振分离到单独的 Hadamard 组合中，允许估计通常需要单独进行 11 分钟编辑实验的七种偶联代谢物的水平。代谢物水平和 CV 与已发表的值吻合良好。对于大多数编辑代谢物，来自多路复用 HERCULES 拟合方法的定量测量的 CV 优于单谱拟合和短 TE PRESS，仅略差或中等程度差于为 tCho、NAA、NAAG 和 Asp 提供最低 CV 的拟合方法。
HERCULES 是一种新的实验方法，具有在 3T 下单个 11 分钟采集内同时编辑和多路复用多达七种偶联低浓度和六种高浓度代谢物的潜力。
