The effect of concomitant gradient fields on diffusion tensor imaging
The effect of concomitant gradient fields on diffusion tensor imaging
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DOI：
10.1002/mrm.24120
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发表时间：
2012-10-01
影响因子：
3.3
通讯作者：
Beaulieu, C.
中科院分区：
文献类型：
--
作者：
Baron, C. A.;Lebel, R. M.;Beaulieu, C.
伴随梯度场是当在磁共振成像中利用磁场梯度时必须存在以满足麦克斯韦方程的横向磁场分量。它们可能具有在较低静态场和/或较高梯度强度下更突出的有害影响。在采用关于重聚焦射频脉冲不对称的大梯度的扩散张量成像方案中（与对称的StejskalTanner不同），伴随场可能导致相位累积，这可能破坏扩散测量。理论预测从这个移相的错误描述和实验验证里斯两次重聚焦和分裂梯度单自旋回波扩散梯度计划。通过实验发现，表观扩散系数值的偏差随着离等中心点的距离以及随着体模和大脑中梯度不对称持续时间的增加而恶化。伴随梯度场的误差量取决于许多变量，包括扩散梯度模式、脉冲序列定时、最大有效梯度幅度、静磁场强度、体素大小、距等中心的切片距离和部分傅立叶分数。提出了一种前瞻性的校正方案，可以减少伴随的梯度误差，并验证了扩散成像。Magn Reson Med，2012年。(c)2011 Wiley Periodicals，Inc.
Concomitant gradient fields are transverse magnetic field components that are necessarily present to satisfy Maxwell's equations when magnetic field gradients are utilized in magnetic resonance imaging. They can have deleterious effects that are more prominent at lower static fields and/or higher gradient strengths. In diffusion tensor imaging schemes that employ large gradients that are not symmetric about a refocusing radiofrequency pulse (unlike StejskalTanner, which is symmetric), concomitant fields may cause phase accrual that could corrupt the diffusion measurement. Theory predicting the error from this dephasing is described and experimentally validated for both Reese twice-refocused and split gradient single spin-echo diffusion gradient schemes. Bias in apparent diffusion coefficient values was experimentally found to worsen with distance from isocenter and with increasing duration of gradient asymmetry in both a phantom and in the brain. The amount of error from concomitant gradient fields depends on many variables, including the diffusion gradient pattern, pulse sequence timing, maximum effective gradient amplitude, static magnetic field strength, voxel size, slice distance from isocenter, and partial Fourier fraction. A prospective correction scheme that can reduce concomitant gradient errors is proposed and verified for diffusion imaging. Magn Reson Med, 2012. (c) 2011 Wiley Periodicals, Inc.