Josef Lissner Laboratory for Biomedical Imaging, Department of Clinical Radiology - Grosshadern, LMU Ludwig Maximilian University of Munich, Marchioninistr. 15, 81377 Munich, Germany.
Eur J Radiol. 2010 Dec;76(3):314-22. doi: 10.1016/j.ejrad.2010.02.018. Epub 2010 Mar 29.
In diffusion-weighted magnetic resonance imaging (DWI), the intensity of the acquired magnetic resonance signal depends on the self-diffusion of the excited spins, i.e., on the microscopic stochastic Brownian molecular motion. Since the extent and orientation of molecular motion is influenced by the microscopic structure and organization of biological tissues, DWI can depict various pathological changes of organs or tissues. While DWI of the brain can be considered an established technique since the mid-1990s, significantly fewer studies have been published about DWI in body imaging, mainly because of the relatively low robustness of conventional DWI methods in non-neurological applications. Consequently, the image quality in such applications was rather limited. This situation, however, improved considerably in recent years due to better hardware as well as new pulse sequences, and several new applications of DWI (e.g., in the abdominal organs, in musculoskeletal applications, or in whole-body protocols) have been described. Unfortunately, DWI of the body is complicated by frequently low signal-to-noise ratios due to shorter transversal (T2) relaxation times and by strong variations of susceptibility. The latter result in severe distortion artifacts when standard echo-planar DWI techniques are applied. Hence, several alternative (non-echo-planar) diffusion-weighting pulse sequence types were proposed and evaluated for DWI applications in the body. In this review article, first the basics of molecular diffusion and of diffusion-weighted MRI are introduced and then several specific MRI techniques, which have been used for DWI of the body, are described. Finally, protocol recommendations for different DWI applications in the body are provided.
在弥散加权磁共振成像（DWI）中，所采集的磁共振信号的强度取决于激发自旋的自扩散，即微观随机布朗分子运动。由于分子运动的程度和方向受到生物组织的微观结构和组织的影响，DWI 可以描绘器官或组织的各种病理变化。虽然脑 DWI 可以被认为是自 20 世纪 90 年代中期以来的一项成熟技术，但在体部成像中发表的 DWI 研究要少得多，主要是因为常规 DWI 方法在非神经应用中的稳健性相对较低。因此，在这些应用中的图像质量受到限制。然而，近年来由于硬件的改进以及新的脉冲序列，这种情况得到了很大改善，并且已经描述了 DWI 的一些新应用（例如在腹部器官、肌肉骨骼应用或全身协议中）。不幸的是，由于较短的横向（T2）弛豫时间和较强的磁化率变化，体部 DWI 经常受到低信噪比的困扰。当应用标准的回波平面 DWI 技术时，这会导致严重的失真伪影。因此，已经提出并评估了几种替代（非回波平面）弥散加权脉冲序列类型，用于体部 DWI 应用。在这篇综述文章中，首先介绍了分子扩散和扩散加权 MRI 的基础知识，然后描述了几种用于体部 DWI 的特定 MRI 技术。最后，提供了不同体部 DWI 应用的协议建议。
