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Non-negative least squares computation for in vivo myelin mapping using simulated multi-echo spin-echo T2 decay data.
NMR in Biomedicine ( IF 2.7 ) Pub Date : 2020-03-02 , DOI: 10.1002/nbm.4277 V Wiggermann 1, 2, 3 , I M Vavasour 3, 4 , S H Kolind 1, 3, 4, 5 , A L MacKay 1, 3, 4 , G Helms 6 , A Rauscher 1, 2, 3, 4
NMR in Biomedicine ( IF 2.7 ) Pub Date : 2020-03-02 , DOI: 10.1002/nbm.4277 V Wiggermann 1, 2, 3 , I M Vavasour 3, 4 , S H Kolind 1, 3, 4, 5 , A L MacKay 1, 3, 4 , G Helms 6 , A Rauscher 1, 2, 3, 4
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Multi‐compartment T2 mapping has gained particular relevance for the study of myelin water in the brain. As a facilitator of rapid saltatory axonal signal transmission, myelin is a cornerstone indicator of white matter development and function. Regularized non‐negative least squares fitting of multi‐echo T2 data has been widely employed for the computation of the myelin water fraction (MWF), and the obtained MWF maps have been histopathologically validated. MWF measurements depend upon the quality of the data acquisition, B1+ homogeneity and a range of fitting parameters. In this special issue article, we discuss the relevance of these factors for the accurate computation of multi‐compartment T2 and MWF maps. We generated multi‐echo spin‐echo T2 decay curves following the Carr‐Purcell‐Meiboom‐Gill approach for various myelin concentrations and myelin T2 scenarios by simulating the evolution of the magnetization vector between echoes based on the Bloch equations. We demonstrated that noise and imperfect refocusing flip angles yield systematic underestimations in MWF and intra−/extracellular water geometric mean T2 (gmT2). MWF estimates were more stable than myelin water gmT2 time across different settings of the T2 analysis. We observed that the lower limit of the T2 distribution grid should be slightly shorter than TE1. Both TE1 and the acquisition echo spacing also have to be sufficiently short to capture the rapidly decaying myelin water T2 signal. Among all parameters of interest, the estimated MWF and intra−/extracellular water gmT2 differed by approximately 0.13–4 percentage points and 3–4 ms, respectively, from the true values, with larger deviations observed in the presence of greater B1+ inhomogeneities and at lower signal‐to‐noise ratio. Tailoring acquisition strategies may allow us to better characterize the T2 distribution, including the myelin water, in vivo.
中文翻译：
使用模拟多回波自旋回波 T2 衰减数据进行体内髓鞘映射的非负最小二乘计算。
多室T 2映射与大脑中髓鞘水的研究特别相关。作为快速跳跃轴突信号传输的促进者，髓鞘是白质发育和功能的基石指标。多回波T 2数据的正则化非负最小二乘拟合已被广泛用于计算髓鞘水分数（MWF），并且获得的 MWF 图已经过组织病理学验证。MWF 测量取决于数据采集的质量、B 1 +均匀性和一系列拟合参数。在这篇特刊文章中，我们讨论了这些因素与准确计算多室T 的相关性2和 MWF 贴图。我们根据 Carr-Purcell-Meiboom-Gill 方法，通过基于 Bloch 方程模拟回波之间磁化矢量的演变，针对各种髓磷脂浓度和髓磷脂T 2场景生成了多回波自旋回波T 2衰减曲线。我们证明了噪声和不完美的重新聚焦翻转角在 MWF 和细胞内/细胞外水几何平均T 2 (gmT 2 ) 中产生系统性低估。在T 2分析的不同设置中，MWF 估计值比髓鞘水 gmT 2时间更稳定。我们观察到T 2 的下限配电网应略短于TE 1 . 两个TE 1和采集回波间隔也必须足够短以捕获迅速衰减的髓鞘水Ť 2信号。在所有感兴趣的参数中，估计的 MWF 和细胞内/细胞外水 gmT 2分别与真实值相差约 0.13-4 个百分点和 3-4 ms，在存在较大B 1 +的情况下观察到更大的偏差不均匀性和较低的信噪比。定制获取策略可以让我们更好地表征T 2 分布，包括髓鞘水，在体内。
更新日期：2020-03-02
中文翻译：
使用模拟多回波自旋回波 T2 衰减数据进行体内髓鞘映射的非负最小二乘计算。
多室T 2映射与大脑中髓鞘水的研究特别相关。作为快速跳跃轴突信号传输的促进者，髓鞘是白质发育和功能的基石指标。多回波T 2数据的正则化非负最小二乘拟合已被广泛用于计算髓鞘水分数（MWF），并且获得的 MWF 图已经过组织病理学验证。MWF 测量取决于数据采集的质量、B 1 +均匀性和一系列拟合参数。在这篇特刊文章中，我们讨论了这些因素与准确计算多室T 的相关性2和 MWF 贴图。我们根据 Carr-Purcell-Meiboom-Gill 方法，通过基于 Bloch 方程模拟回波之间磁化矢量的演变，针对各种髓磷脂浓度和髓磷脂T 2场景生成了多回波自旋回波T 2衰减曲线。我们证明了噪声和不完美的重新聚焦翻转角在 MWF 和细胞内/细胞外水几何平均T 2 (gmT 2 ) 中产生系统性低估。在T 2分析的不同设置中，MWF 估计值比髓鞘水 gmT 2时间更稳定。我们观察到T 2 的下限配电网应略短于TE 1 . 两个TE 1和采集回波间隔也必须足够短以捕获迅速衰减的髓鞘水Ť 2信号。在所有感兴趣的参数中，估计的 MWF 和细胞内/细胞外水 gmT 2分别与真实值相差约 0.13-4 个百分点和 3-4 ms，在存在较大B 1 +的情况下观察到更大的偏差不均匀性和较低的信噪比。定制获取策略可以让我们更好地表征T 2 分布，包括髓鞘水，在体内。
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