Robert Steiner MR Unit, Imaging Sciences Department, MRC Clinical Sciences Centre, Hammersmith Hospital, Imperial College London, London, UK.
Magn Reson Imaging. 2011 Jun;29(5):659-67. doi: 10.1016/j.mri.2011.02.015. Epub 2011 Apr 29.
Echo-planar diffusion-weighted images can display significant geometric distortions due to eddy current fields. Several preparation schemes have been proposed, which can null eddy currents with a single time constant. The aim of this work was to compare the performance of three such pulse sequences in the presence of multiple components and investigate whether affine registration is capable of correcting for the resulting distortions. A magnetic resonance imaging simulator was used to eliminate potential confounding factors. The doubly refocused sequences showed substantially reduced effects. Applying affine registration to the single spin-echo images leads to reduced residuals, but not to the level observed for the doubly refocused sequences. Modified versions of the standard single spin-echo and doubly refocused sequences performed better than their original counterparts. Affine registration is not sufficient to correct for strong eddy current effects, which should therefore be minimized at source. When the use of a doubly refocused sequence is not possible, a modified single spin-echo sequence should be considered.
基于平面回波的弥散加权成像由于涡流场的存在会产生明显的几何变形。已经提出了几种预备方案，可以用单一时间常数来抵消涡流。本研究的目的是比较三种这样的脉冲序列在多分量存在下的性能，并研究仿射配准是否能够纠正由此产生的变形。磁共振成像模拟器被用来消除潜在的混杂因素。双反转聚焦序列显示出明显降低的效果。对单自旋回波图像应用仿射配准会导致残差减少，但不会达到双反转聚焦序列的水平。标准单自旋回波和双反转聚焦序列的修正版本比它们的原始版本表现更好。仿射配准不足以纠正强涡流效应，因此应在源头上尽量减少涡流效应。当无法使用双反转聚焦序列时，应考虑使用修正的单自旋回波序列。
