PGSE, OGSE, and sensitivity to axon diameter in diffusion MRI: Insight from a simulation study.
PGSE, OGSE, and sensitivity to axon diameter in diffusion MRI: Insight from a simulation study.
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DOI：
10.1002/mrm.25631
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发表时间：
2016-02
影响因子：
3.3
通讯作者：
Alexander DC
中科院分区：
文献类型：
--
作者：
Drobnjak I;Zhang H;Ianuş A;Kaden E;Alexander DC
确定最佳脉冲梯度自旋回波（PGSE）和振荡梯度自旋回波（OGSE）序列设置，以在理想和实际条件下最大限度地提高对轴突直径的灵敏度。对简单的双室白质模型（具有非渗透性圆柱体）的模拟用于研究具有梯形扩散梯度波形的临床上合理的 PGSE 和 OGSE 序列参数。信号灵敏度作为信号相对于轴突直径的导数来测量。分别研究平行和分散纤维模型以代表理想和实际条件。模拟表明，对于梯度完全垂直于直平行纤维的简单情况，PGSE 始终给出最大灵敏度。然而，在纤维具有未知且分散方向的现实场景中，低频 OGSE 提供了更高的灵敏度。最大灵敏度结果表明，在当前的临床扫描仪（G max = 60 mT/m，信噪比（SNR） = 20）上，轴突直径低于 6 µm 与零无法区分。具有更强梯度系统的扫描仪，例如麻省总医院 (MGH) Connectom 扫描仪 (G max = 300 mT/m) 可以将此灵敏度限制扩展到 2–3 µm，探测更大比例的底层轴突直径分布。在实际情况下，低频 OGSE 为 PGSE 提供了额外的灵敏度。 OGSE 对于具有高性能梯度的系统特别有利。 Magn Reson Med 75:688–700, 2016。© 2015 The Authors Magnetic Resonance in Medicine 由 Wiley periodicals, Inc. 代表国际医学磁共振学会出版。这是一篇根据知识共享署名许可条款的开放获取文章，允许在任何媒体上使用、分发和复制，前提是正确引用了原始作品。
To identify optimal pulsed gradient spin‐echo (PGSE) and oscillating gradient spin‐echo (OGSE) sequence settings for maximizing sensitivity to axon diameter in idealized and practical conditions. Simulations on a simple two‐compartment white matter model (with nonpermeable cylinders) are used to investigate a wide space of clinically plausible PGSE and OGSE sequence parameters with trapezoidal diffusion gradient waveforms. Signal sensitivity is measured as a derivative of the signal with respect to axon diameter. Models of parallel and dispersed fibers are investigated separately to represent idealized and practical conditions. Simulations show that, for the simple case of gradients perfectly perpendicular to straight parallel fibers, PGSE always gives maximum sensitivity. However, in real‐world scenarios where fibers have unknown and dispersed orientation, low‐frequency OGSE provides higher sensitivity. Maximum sensitivity results show that on current clinical scanners (G max = 60 mT/m, signal to noise ratio (SNR) = 20) axon diameters below 6 µm are indistinguishable from zero. Scanners with stronger gradient systems such as the Massachusetts General Hospital (MGH) Connectom scanner (G max = 300 mT/m) can extend this sensitivity limit down to 2–3 µm, probing a much greater proportion of the underlying axon diameter distribution. Low‐frequency OGSE provides additional sensitivity to PGSE in practical situations. OGSE is particularly advantageous for systems with high performance gradients. Magn Reson Med 75:688–700, 2016. © 2015 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.