Department of Biomedical Magnetic Resonance, Institute for Experimental Physics, Otto-von-Guericke University Magdeburg, Germany; Department of Neurologic Surgery, Mayo Clinic, Rochester, MN, USA.
Department of Biomedical Magnetic Resonance, Institute for Experimental Physics, Otto-von-Guericke University Magdeburg, Germany.
Neuroimage. 2017 Mar 1;148:20-30. doi: 10.1016/j.neuroimage.2017.01.008. Epub 2017 Jan 5.
High-resolution diffusion-weighted imaging (DWI) has great potential to provide unique information about tissue microstructure in-vivo. Although single-shot echo-planar imaging (EPI) is a most popular tool for DWI, its application for high-resolution DWI is limited due to T2* blurring and susceptibility- and eddy-current-induced geometric distortions, especially at ultra-high field (UHF) such as 7T. In this study, we adapt a hybrid spin-warp and echo-planar encoding strategy inspired by point spread function (PSF) mapping and optimize it for high-resolution and distortion-free diffusion imaging applications. More specifically, a 2D navigator echo is added into the original sequence for shot-to-shot motion-induced phase error estimation and correction. The spatial encoding is shared between the PSF and the EPI phase encoding dimension allowing short echo trains to preserve the diffusion and navigator signals efficiently at UHF, where T2 decay is relatively fast. In addition, variable k-space spacing was applied in the PSF dimension and combined with parallel imaging in the EPI-PE dimension to further accelerate the PSF acquisition. The results demonstrate that this method can yield isotropic submillimeter resolution without T2* blurring and geometric distortions at 7T and enables a clear and detailed delineation of human brain structures in-vivo with the diffusion contrasts. In addition, results of the proposed approach for high-resolution diffusion imaging at 3T are presented.
高分辨率弥散加权成像（DWI）具有提供组织微观结构体内独特信息的巨大潜力。虽然单次激发回波平面成像（EPI）是 DWI 最常用的工具，但由于 T2* 弥散和磁敏感性及涡流引起的几何变形，特别是在超高场（UHF）如 7T，其在高分辨率 DWI 中的应用受到限制。在这项研究中，我们受到点扩散函数（PSF）映射的启发，采用了一种混合自旋缠绕和 EPI 编码策略，并对其进行了优化，以实现高分辨率和无失真的扩散成像应用。更具体地说，在原始序列中添加了一个 2D 导航回波，用于估计和校正每个激发之间的运动引起的相位误差。PSF 和 EPI 相位编码维度之间共享空间编码，允许短回波链在 UHF 下高效地保留扩散和导航信号，因为 T2 衰减在 UHF 下相对较快。此外，在 PSF 维度上应用了可变的 K 空间间距，并在 EPI-PE 维度上结合并行成像，进一步加速 PSF 采集。结果表明，该方法可以在 7T 下获得各向同性亚毫米分辨率，无 T2* 弥散和几何变形，并能够在体内用弥散对比清晰、详细地描绘出人脑结构。此外，还展示了在 3T 下进行高分辨率扩散成像的建议方法的结果。
