Slice-direction geometric distortion evaluation and correction with reversed slice-select gradient acquisitions.
Slice-direction geometric distortion evaluation and correction with reversed slice-select gradient acquisitions.
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DOI：
10.1016/j.neuroimage.2022.119701
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发表时间：
2022-12-01
期刊：
影响因子：
5.7
通讯作者：
Polimeni, Jonathan R.
中科院分区：
文献类型：
--
作者：
Blazejewska, Anna, I;Witzel, Thomas;Andersson, Jesper L. R.;Wald, Lawrence L.;Polimeni, Jonathan R.
在同一受试者的多个对比度上采集的MRI数据的准确空间对齐对于数据分析和解释通常是至关重要的，但是在采集之间存在不同的几何失真的情况下可能具有挑战性。众所周知，单次激发回波平面成像（EPI）采集由于由组织磁化率差异和其他源引起的B0场不均匀性而遭受相位编码方向上的失真，然而，在存在强场不均匀性的情况下，在其他编码方向上也可能存在失真。高分辨率超高场MRI通常在切片编码方向上使用低带宽来采集薄切片，并且当与明显的B0不均匀性相结合时，也容易在切片方向上产生额外的几何失真。在这里，我们证明了这种切片失真的存在下，在高分辨率的7T EPI收购一种新的脉冲序列，允许反转的切片编码梯度极性，使收购的图像对在切片方向上的失真幅度相等，但极性相反。我们还表明，切片方向失真可以使用基于梯度反转的方法进行校正，应用相同的软件用于相位编码方向失真的常规校正。
Accurate spatial alignment of MRI data acquired across multiple contrasts in the same subject is often crucial for data analysis and interpretation, but can be challenging in the presence of geometric distortions that differ between acquisitions. It is well known that single-shot echo-planar imaging (EPI) acquisitions suffer from distortion in the phase-encoding direction due to B0 field inhomogeneities arising from tissue magnetic susceptibility differences and other sources, however there can be distortion in other encoding directions as well in the presence of strong field inhomogeneities. High-resolution ultrahigh-field MRI typically uses low bandwidth in the slice-encoding direction to acquire thin slices and, when combined with the pronounced B0 inhomogeneities, is prone to an additional geometric distortion in the slice direction as well. Here we demonstrate the presence of this slice distortion in high-resolution 7T EPI acquired with a novel pulse sequence allowing for the reversal of the slice-encoding gradient polarity that enables the acquisition of pairs of images with equal magnitudes of distortion in the slice direction but with opposing polarities. We also show that the slice-direction distortion can be corrected using gradient reversal-based method applying the same software used for conventional corrections of phase-encoding direction distortion.
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