Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, UT, United States of America; Department of Biomedical Engineering, University of Utah, Salt Lake City, UT, United States of America.
Department of Biomedical Engineering, University of Utah, Salt Lake City, UT, United States of America.
Magn Reson Imaging. 2019 Sep;61:273-284. doi: 10.1016/j.mri.2019.04.008. Epub 2019 Apr 19.
The main objective of this study is to develop a 2D single-shot radial-DWI (2D ss-rDWI) technique to reduce motion artifacts and geometric distortion in DW images.
A diffusion-preparation module is developed and applied prior to the data acquisition. Because the diffusion-prepared longitudinal magnetization is measured over multiple RF excitations in each shot, 2D ss-rDWI is subject to low signal-to-noise ratio (SNR). We used variable-flip angle (VFA), random view ordering (RVO), and sliding spokes, and compared the performances to constant flip angle (CFA), smooth view ordering (SVO), and identical spoke averaging, respectively. For each technique, we performed numerical simulation and MRI experiments on a fluid phantom as well as in-vivo human brain studies with a 3 T MRI system.
Using VFA, optimal SNR was acquired for 2D ss-rDWI. Using SVO, the high signal is clustered at specific quadrant in 2D k-space: the first quadrant using high initial flip angle or the last quadrant using the low flip angle. This clustered signal in k-space led to geometric distortion in image space. 2D ss-rDWI using RVO spreads the high signaled spokes over all angular directions and removes the view-order-related distortion. The in-vivo images using 2D ss-rDWI with VFA and RVO show no geometric distortion at the skull base brain, but greatly reduced SNR compared with those using 2D ss-DWEPI.
2D ss-rDWI is optimized by using VFA with RVO. The resultant DWI using 2D ss-rDWI is insensitive to motion-induced artifacts and geometric distortion. Even with low SNR, it may be useful for DWI of organs limited by severe susceptibility-induced geometric distortion.
本研究的主要目的是开发一种二维单次激发径向弥散加权成像（2D ss-rDWI）技术，以减少 DW 图像中的运动伪影和几何变形。
开发了一个扩散准备模块，并在数据采集之前应用。由于在每个激发中，扩散准备的纵向磁化强度是在多个 RF 激发上测量的，因此 2D ss-rDWI 的信噪比（SNR）较低。我们使用了可变翻转角（VFA）、随机视图排序（RVO）和滑动 spokes，并分别与恒定翻转角（CFA）、平滑视图排序（SVO）和相同的 spoke 平均进行了比较。对于每种技术，我们在流体体模上进行了数值模拟和 MRI 实验，以及在 3T MRI 系统上进行了活体人脑研究。
使用 VFA，可获得 2D ss-rDWI 的最佳 SNR。使用 SVO，在 2D k 空间中，高信号聚集在特定象限：使用高初始翻转角的第一象限或使用低翻转角的最后象限。这种在 k 空间中聚集的信号导致图像空间中的几何变形。使用 RVO 的 2D ss-rDWI 将高信号 spokes散布在所有角度方向上，并消除了与视图顺序相关的失真。使用 VFA 和 RVO 的 2D ss-rDWI 进行的活体图像在颅底大脑处没有几何变形，但与使用 2D ss-DWEPI 的图像相比，SNR 大大降低。
通过使用 RVO 与 VFA 相结合，优化了 2D ss-rDWI。使用 2D ss-rDWI 的结果 DWI 对运动引起的伪影和几何变形不敏感。即使 SNR 较低，它也可能对受严重磁化率诱导几何变形限制的器官的 DWI 有用。
