Maier Stephan E
Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
Neurotherapeutics. 2007 Jul;4(3):453-9. doi: 10.1016/j.nurt.2007.05.003.
Magnetic resonance diffusion tensor imaging yields images with detailed information about tissue water diffusion. Diffusion-weighted imaging of the human spinal cord requires dedicated magnetic resonance pulse sequences that minimize the effects of subject motion, distortions, and artifacts from lipids and CSF flow. These problems are accentuated by the anatomic properties of the spinal cord (i.e., a small cross-sectional dimension and a location deep inside the body). The diffusion tensor (a simplified model for complex diffusion in structured tissues) can be estimated for each image pixel by measuring diffusion along a minimum of six independent directions. It can then be used to derive mean diffusivity, diffusion anisotropy, and the dominant orientation of the diffusion process. The observation that diffusion along nerve fibers is much higher than across fibers, allows a noninvasive reconstruction of the spinal cord nerve fiber architecture. This includes not only the primary cranio-caudad running connections, but also secondary, transverse running collateral fibers. With fiber tracking, the pixel-based diffusion information can be integrated to obtain a three-dimensional view of axonal fiber connectivity between the spinal cord and different brain regions. The development and myelination during infancy and early childhood is reflected in a gradual decrease of mean diffusivity and increase in anisotropy. There are several diseases that lead to either local or general changes in spinal cord water diffusion. For therapy research, such changes can be studied noninvasively and repeatedly in animal models.
磁共振扩散张量成像可生成包含组织水扩散详细信息的图像。对人类脊髓进行扩散加权成像需要专门的磁共振脉冲序列，以尽量减少受试者运动、畸变以及来自脂质和脑脊液流动的伪影的影响。脊髓的解剖特性（即横截面尺寸小且位于身体深部）会加剧这些问题。通过沿至少六个独立方向测量扩散，可为每个图像像素估计扩散张量（结构化组织中复杂扩散的简化模型）。然后可用于推导平均扩散率、扩散各向异性以及扩散过程的主要方向。沿神经纤维的扩散远高于跨纤维的扩散这一观察结果，使得能够对脊髓神经纤维结构进行无创重建。这不仅包括主要的头尾向运行连接，还包括次要的横向运行侧支纤维。通过纤维追踪，基于像素的扩散信息可被整合，以获得脊髓与不同脑区之间轴突纤维连接性的三维视图。婴儿期和幼儿期的发育和髓鞘形成表现为平均扩散率逐渐降低和各向异性增加。有几种疾病会导致脊髓水扩散的局部或总体变化。对于治疗研究，可在动物模型中对这些变化进行无创且重复的研究。
