Hajnal J V, Doran M, Hall A S, Collins A G, Oatridge A, Pennock J M, Young I R, Bydder G M
GEC Hirst Research Centre, Wembley, Middlesex.
J Comput Assist Tomogr. 1991 Jan-Feb;15(1):1-18. doi: 10.1097/00004728-199101000-00001.
The use of MR imaging to image anisotropically restricted diffusion (ARD) of water in the nervous system is described. The theoretical basis for the use of the pulsed gradient spin echo sequences is outlined, including an estimate of the range of cell dimensions that can be studied with this technique. The importance of restricted diffusion across myelinated white matter fibre tracts is emphasised and the capacity of MR imaging to demonstrate fibre pathways as a function of their direction is illustrated. Technical developments that have been implemented include 256 x 256 spatial resolution, a wider range of diffusion times Td, and an increased range of diffusion sensitivity parameters b. Effects of these are illustrated together with the use of gradient moment nulling methods, oblique sensitisation, and a smaller set of gradient coils that enable shorter values of echo time to be used with the same value of b. The anatomical basis for ARD imaging is analysed, and association, commissural, and projection fibre tracts are demonstrated in different planes. The published literature on variations of the apparent diffusion coefficient from normal is reviewed and examples where diffusion weighted images revealed information that was not necessarily apparent with conventional sequences are illustrated. These include cases of multiple sclerosis, chronic head injury, progressive multifocal leucoencephalopathy, cerebrovascular disease, astrocytoma, and probable metastases to the brain. Imaging of ARD affords a fascinating conjunction between the microscopic movement of water, the properties of myelinated white matter fibres, gross anatomy of the brain, and changes of the diffusion of water in disease.
本文描述了利用磁共振成像（MR成像）对神经系统中水分子各向异性受限扩散（ARD）进行成像的方法。概述了使用脉冲梯度自旋回波序列的理论基础，包括对该技术可研究的细胞尺寸范围的估计。强调了髓鞘化白质纤维束中受限扩散的重要性，并展示了MR成像根据纤维方向显示纤维通路的能力。已实施的技术改进包括256×256的空间分辨率、更广泛的扩散时间Td范围以及更大的扩散敏感参数b范围。阐述了这些改进的效果，以及梯度矩归零方法、倾斜敏感化的应用，还有一组较小的梯度线圈，使得在相同的b值下能够使用更短的回波时间。分析了ARD成像的解剖学基础，并在不同平面上展示了联合纤维束、连合纤维束和投射纤维束。回顾了关于表观扩散系数与正常情况差异的已发表文献，并举例说明了扩散加权成像揭示的信息在传统序列中不一定明显的情况。这些例子包括多发性硬化症、慢性头部损伤、进行性多灶性白质脑病、脑血管疾病、星形细胞瘤以及可能的脑转移瘤。ARD成像实现了水分子微观运动、髓鞘化白质纤维特性、大脑大体解剖结构以及疾病中水分子扩散变化之间引人入胜的结合。
