C. J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.
Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland.
NMR Biomed. 2023 Jan;36(1):e4822. doi: 10.1002/nbm.4822. Epub 2022 Sep 13.
The purpose of this study was to develop a self-navigation strategy to improve scan efficiency and image quality of water/fat-separated, diffusion-weighted multishot echo-planar imaging (ms-EPI). This is accomplished by acquiring chemical shift-encoded diffusion-weighted data and using an appropriate water-fat and diffusion-encoded signal model to enable reconstruction directly from k-space data. Multishot EPI provides reduced geometric distortion and improved signal-to-noise ratio in diffusion-weighted imaging compared with single-shot approaches. Multishot acquisitions require corrections for physiological motion-induced shot-to-shot phase errors using either extra navigators or self-navigation principles. In addition, proper fat suppression is important, especially in regions with large B inhomogeneity. This makes the use of chemical shift encoding attractive. However, when combined with ms-EPI, shot-to-shot phase navigation can be challenging because of the spatial displacement of fat signals along the phase-encoding direction. In this work, a new model-based, self-navigated water/fat separation reconstruction algorithm is proposed. Experiments in legs and in the head-neck region of 10 subjects were performed to validate the algorithm. The results are compared with an image-based, two-dimensional (2D) navigated water/fat separation approach for ms-EPI and with a conventional fat saturation approach. Compared with the 2D navigated method, the use of self-navigation reduced the shot duration time by 30%-35%. The proposed algorithm provided improved diffusion-weighted water images in both leg and head-neck regions compared with the 2D navigator-based approach. The proposed algorithm also produced better fat suppression compared with the conventional fat saturation technique in the B inhomogeneous regions. In conclusion, the proposed self-navigated reconstruction algorithm can produce superior water-only diffusion-weighted EPI images with less artefacts compared with the existing methods.
本研究旨在开发一种自导航策略，以提高水脂分离、扩散加权多 shot 回波平面成像（ms-EPI）的扫描效率和图像质量。这是通过采集化学位移编码扩散加权数据并使用适当的水脂和扩散编码信号模型来实现的，从而能够直接从 k 空间数据进行重建。与单 shot 方法相比，多 shot EPI 可在扩散加权成像中提供更小的几何变形和更高的信噪比。多 shot 采集需要使用额外的导航器或自导航原理校正生理运动引起的 shot-to-shot 相位误差。此外，适当的脂肪抑制非常重要，尤其是在大 B 不均匀性区域。这使得化学位移编码的使用具有吸引力。然而，当与 ms-EPI 结合使用时，由于脂肪信号沿相位编码方向的空间位移，shot-to-shot 相位导航可能具有挑战性。在这项工作中，提出了一种新的基于模型的自导航水脂分离重建算法。在 10 名受试者的腿部和头颈部进行了实验，以验证该算法。结果与基于图像的二维（2D）导航水脂分离方法和常规脂肪饱和方法进行了比较。与二维导航方法相比，自导航的使用将拍摄时间减少了 30%-35%。与基于二维导航器的方法相比，所提出的算法在腿部和头颈部区域提供了改进的扩散加权水图像。与传统的脂肪饱和技术相比，所提出的算法在 B 不均匀性区域还提供了更好的脂肪抑制效果。总之，与现有的方法相比，所提出的自导航重建算法可以产生具有更少伪影的优越的仅水扩散加权 EPI 图像。
