DTU Compute, Technical University of Denmark, Lyngby, Denmark.
Department of Clinical Physiology, Nuclear Medicine & PET, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark.
Magn Reson Med. 2022 Feb;87(2):629-645. doi: 10.1002/mrm.28991. Epub 2021 Sep 7.
To compare prospective motion correction (PMC) and retrospective motion correction (RMC) in Cartesian 3D-encoded MPRAGE scans and to investigate the effects of correction frequency and parallel imaging on the performance of RMC.
Head motion was estimated using a markerless tracking system and sent to a modified MPRAGE sequence, which can continuously update the imaging FOV to perform PMC. The prospective correction was applied either before each echo train (before-ET) or at every sixth readout within the ET (within-ET). RMC was applied during image reconstruction by adjusting k-space trajectories according to the measured motion. The motion correction frequency was retrospectively increased with RMC or decreased with reverse RMC. Phantom and in vivo experiments were used to compare PMC and RMC, as well as to compare within-ET and before-ET correction frequency during continuous motion. The correction quality was quantitatively evaluated using the structural similarity index measure with a reference image without motion correction and without intentional motion.
PMC resulted in superior image quality compared to RMC both visually and quantitatively. Increasing the correction frequency from before-ET to within-ET reduced the motion artifacts in RMC. A hybrid PMC and RMC correction, that is, retrospectively increasing the correction frequency of before-ET PMC to within-ET, also reduced motion artifacts. Inferior performance of RMC compared to PMC was shown with GRAPPA calibration data without intentional motion and without any GRAPPA acceleration.
Reductions in local Nyquist violations with PMC resulted in superior image quality compared to RMC. Increasing the motion correction frequency to within-ET reduced the motion artifacts in both RMC and PMC.
比较笛卡尔三维编码 MPRAGE 扫描中的前瞻性运动校正（PMC）和回顾性运动校正（RMC），并研究校正频率和平行成像对 RMC 性能的影响。
使用无标记跟踪系统估计头部运动，并将其发送到经过修改的 MPRAGE 序列，该序列可以连续更新成像视野以进行 PMC。前瞻性校正可以在每个回波链之前（前 ET）或在回波链内的每第六次读出时（内 ET）应用。通过根据测量的运动调整 k 空间轨迹，在图像重建期间应用 RMC。通过反向 RMC 可以减少 RMC 的运动校正频率，或者通过 RMC 增加运动校正频率。使用幻影和体内实验来比较 PMC 和 RMC，以及在连续运动期间比较内 ET 和前 ET 的校正频率。使用结构相似性指数测量来定量评估校正质量，参考图像没有运动校正且没有故意运动。
与 RMC 相比，PMC 在视觉和定量方面都能获得更好的图像质量。将校正频率从前 ET 增加到内 ET 会减少 RMC 中的运动伪影。通过将前 ET PMC 的校正频率回溯性地增加到内 ET，实现了 PMC 和 RMC 的混合校正，也减少了运动伪影。与 PMC 相比，在没有故意运动和没有任何 GRAPPA 加速的情况下，使用 GRAPPA 校准数据的 RMC 表现不佳。
与 RMC 相比，PMC 减少局部奈奎斯特违规导致的图像质量更好。将运动校正频率增加到内 ET 可以减少 RMC 和 PMC 中的运动伪影。
