High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University Vienna, Vienna, Austria.
Neuroscience Center, University of Helsinki, Helsinki, Finland.
Magn Reson Med. 2021 Apr;85(4):1909-1923. doi: 10.1002/mrm.28555. Epub 2020 Nov 9.
To explore the impact of temporal motion-induced coil sensitivity changes on CEST-MRI at 7T and its correction using interleaved volumetric EPI navigators, which are applied for real-time motion correction.
Five healthy volunteers were scanned via CEST. A 4-fold correction pipeline allowed the mitigation of (1) motion, (2) motion-induced coil sensitivity variations, , (3) motion-induced static magnetic field inhomogeneities, ΔB , and (4) spatially varying transmit RF field fluctuations, . Four CEST measurements were performed per session. For the first 2, motion correction was turned OFF and then ON in absence of voluntary motion, whereas in the other 2 controlled head rotations were performed. During post-processing was removed additionally for the motion-corrected cases, resulting in a total of 6 scenarios to be compared. In all cases, retrospective ∆B and - corrections were performed to compute artifact-free magnetization transfer ratio maps with asymmetric analysis (MTR ).
Dynamic correction successfully mitigated signal deviations caused by head motion. In 2 frontal lobe regions of volunteer 4, induced relative signal errors of 10.9% and 3.9% were reduced to 1.1% and 1.0% after correction. In the right frontal lobe, the motion-corrected MTR contrast deviated 0.92%, 1.21%, and 2.97% relative to the static case for Δω = 1, 2, 3 ± 0.25 ppm. The additional application of correction reduced these deviations to 0.10%, 0.14%, and 0.42%. The fully corrected MTR values were highly consistent between measurements with and without intended head rotations.
Temporal cause significant CEST quantification bias. The presented correction pipeline including the proposed retrospective correction significantly reduced motion-related artifacts on CEST-MRI.
探索在 7T 下，时间运动引起的线圈灵敏度变化对 CEST-MRI 的影响，并使用交错容积 EPI 导航仪进行校正，该导航仪用于实时运动校正。
5 名健康志愿者进行了 CEST 扫描。采用 4 倍校正流水线，可以减轻（1）运动，（2）运动引起的线圈灵敏度变化，（3）运动引起的静态磁场不均匀性，ΔB，和（4）空间变化的发射 RF 场波动，。每次扫描进行 4 次 CEST 测量。在前 2 次测量中，在没有自愿运动的情况下关闭和打开运动校正，而在后 2 次测量中则进行受控的头部旋转。在后期处理中，还去除了运动校正的情况，总共比较了 6 种情况。在所有情况下，都进行了回顾性ΔB 和-校正，以计算具有非对称分析（MTR）的无伪影磁化转移率图。
动态校正成功地减轻了头部运动引起的信号偏差。在志愿者 4 的 2 个额区，校正后相对信号误差从 10.9%和 3.9%分别降低到 1.1%和 1.0%。在右额叶，与静态情况相比，在Δω=1、2、3±0.25 ppm 时，运动校正的 MTR 对比度分别偏离 0.92%、1.21%和 2.97%。应用额外的校正后，这些偏差分别降低到 0.10%、0.14%和 0.42%。有和没有预期头部旋转的测量之间的完全校正的 MTR 值高度一致。
时间运动引起的线圈灵敏度变化会导致 CEST 定量分析出现显著偏差。所提出的包括拟议的回顾性校正的校正流水线显著降低了 CEST-MRI 上的运动相关伪影。
