Highly Accelerated Distortion-Free Diffusion-WeightedMR Imaging at Ultra High Field (7T): Gray Matter Characterization

超高场（UHF）单次回波平面成像（EPI）实现了高空间分辨率的快速脑成像。这对于功能磁共振成像（fMRI）和弥散加权成像（DWI）研究脑功能的测量和脑组织微观结构信息的表征非常有利，并可作为一种标准方法。然而，EPI中一个众所周知的问题是强磁化率引起的几何畸变，特别是在UHF如7T下。此外，在DWI中，EPI中的畸变由于涡流的影响而随扩散编码梯度的方向而变化，成为一个主要的挑战。在本项目的第一个资助期内（2012-2015），我们成功实现了fMRI的在线畸变校正包，并将该方法扩展到DWI。由于EPI的空间分辨率有限，在皮质区域出现强烈的失真和信号丢失。因此，到目前为止，DWI几乎只用于白质（WM）的结构和病理研究。作为标准EPI的替代方案，我们开发了一种新的无失真技术，可以实现前所未有的高空间分辨率和保真度的活体人脑DWI。虽然延长了测量时间，但我们的新方法可以无创地获取灰质微观结构。在这个项目的延续,我们的目标覆盖我)全面发展全面的(即易感性,eddy-current-induced)失真校正方案及其实现标准醉酒驾车,ii)进一步研究高分辨率酒后驾驶我们的新技术来减少扫描时间,提高图像保真度通过抑制流motion-induced工件,和iii)详细的灰质体内表征扩散使用扩散图像的高分辨率。这将首次在体内全面表征整个人类大脑的灰质扩散，并为未来的科学和临床应用提供参考。

Single-shot echo-planar imaging (EPI) at ultra-high field (UHF) enables fast brain imaging with high spatial resolution. It is very beneficial for functional magnetic resonance imaging (fMRI) and diffusion weighted imaging (DWI) studies to measure brain function and to characterize information about brain tissue microstructure and used as a standard method. However, a well-known problem in EPI is strong susceptibility-induced geometric distortion, especially at UHF such as 7T. In DWI, in addition, distortions in EPI vary due to eddy-currents depending on the direction of diffusion encoding gradients and become a major challenge. During the first funding period of this project (2012-2015) we have successfully implemented an online distortion correction package for fMRI and extended the method to DWI. Due to limited spatial resolution of EPI, strong distortions, and signal loss appear in cortical regions. Therefore, DWI has been applied almost exclusively to the investigation of structure and pathology in white matter (WM) up to now. As an alternative to standard EPI, we developed a novel distortion-free technique that allows unprecedented high spatial resolution and fidelity of in vivo human brain DWI. With our new method, gray matter microstructure becomes accessible non-invasively although measurement times are prolonged. In the continuation of this project, our goal covers i) full development of a comprehensive (i.e. susceptibility- and eddy-current-induced) distortion correction package and its implementation for standard DWI, ii) further research on our new technique for very high-resolution DWI to reduce scan time and improve the image fidelity by suppressing flow- and motion-induced artifacts, and iii) detailed in vivo characterization of gray matter diffusion using very high-resolution diffusion images. This will allow comprehensive characterization of gray matter diffusion in the entire human brain in vivo for the first time and serve as a reference for future scientific and clinical applications.