Maier S E
Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
Magn Reson Med. 2001 Dec;46(6):1136-43. doi: 10.1002/mrm.1310.
For maximum robustness of a diffusion-weighted MR imaging sequence, it is desirable to use a single-shot imaging method. This article introduces a new single-shot imaging approach that combines the advantages of multiple spin-echoes with the technique of line scan diffusion imaging. A slab volume, which can be spatially encoded with fewer phase encodes than a regular field of view, is selected with 2D selective pulses. With the shorter echo train, the sensitivity to field inhomogeneities and chemical shift is thus greatly diminished. Further reduction is achieved by interleaving short gradient echo trains with refocusing spin-echo pulses. Optimized slice-selective RF pulses that produce flip angles close to 180 degrees are used to minimize the stimulated echo component. Motion-related phase shifts, which change polarity with each spin-echo excitation, will give rise to artifacts that are avoidable by processing even and odd spin-echoes separately. As with line scan diffusion imaging, the complete field of view is acquired by sequential scanning. Since with each shot several lines of data are collected, a considerable improvement over line scan diffusion imaging in terms of scanning speed is achieved. Diffusion data obtained in phantoms and normal subjects demonstrate the feasibility of this novel approach.
为使扩散加权磁共振成像序列具有最大的稳健性，采用单次成像方法是可取的。本文介绍了一种新的单次成像方法，该方法结合了多个自旋回波的优点和线扫描扩散成像技术。使用二维选择性脉冲选择一个板层体积，与常规视野相比，该板层体积可以用更少的相位编码进行空间编码。由于回波链较短，因此对场不均匀性和化学位移的敏感性大大降低。通过将短梯度回波链与重聚焦自旋回波脉冲交错排列可进一步降低敏感性。使用产生接近180度翻转角的优化切片选择性射频脉冲，以尽量减少受激回波分量。与每个自旋回波激发极性相反的运动相关相移会产生伪影，通过分别处理偶数和奇数自旋回波可以避免这些伪影。与线扫描扩散成像一样，通过顺序扫描获取完整的视野。由于每次扫描采集几行数据，因此在扫描速度方面比线扫描扩散成像有了显著提高。在体模和正常受试者中获得的扩散数据证明了这种新方法的可行性。
