Department of Nuclear Medicine and Molecular Imaging, University of Groningen, University Medical Center Groningen, 9713 GZ Groningen, The Netherlands.
Department of Neuroscience, Imaging, and Clinical Sciences, Institute for Advanced Biomedical Technologies, 'G. d'Annunzio' University of Chieti-Pescara, 66100 Chieti, Italy.
Brain. 2023 Apr 19;146(4):1243-1266. doi: 10.1093/brain/awac436.
Myelin is the protective sheath wrapped around axons, consisting of a phospholipid bilayer with water between the wraps. The measurement of damage to the myelin sheaths, the evaluation of the efficacy of therapies aiming to promote remyelination and monitoring the degree of brain maturation in children all require non-invasive quantitative myelin imaging methods. To date, various myelin imaging techniques have been developed. Five different MRI approaches can be distinguished based on their biophysical principles: (i) imaging of the water between the lipid bilayers directly (e.g. myelin water imaging); (ii) imaging the non-aqueous protons of the phospholipid bilayer directly with ultra-short echo-time techniques; (iii) indirect imaging of the macromolecular content (e.g. magnetization transfer; inhomogeneous magnetization transfer); (iv) mapping of the effects of the myelin sheath's magnetic susceptibility on the MRI signal (e.g. quantitative susceptibility mapping); and (v) mapping of the effects of the myelin sheath on water diffusion. Myelin imaging with PET uses radioactive molecules with high affinity to specific myelin components, in particular myelin basic protein. This review aims to give an overview of the various myelin imaging techniques, their biophysical principles, image acquisition, data analysis and their validation status.
髓鞘是包裹在轴突周围的保护鞘，由一个磷脂双层组成，双层之间有水。测量髓鞘的损伤程度、评估旨在促进髓鞘再生的治疗效果以及监测儿童大脑成熟程度都需要非侵入性的定量髓鞘成像方法。迄今为止，已经开发出了各种髓鞘成像技术。根据其生物物理原理，可以将五种不同的 MRI 方法区分开来：（i）直接成像脂质双层之间的水（例如，髓鞘水成像）；（ii）直接使用超短回波时间技术成像磷脂双层的非水质子；（iii）间接成像大分子含量（例如，磁化转移；不均匀磁化转移）；（iv）绘制髓鞘的磁导率对 MRI 信号的影响图（例如，定量磁化率映射）；和（v）绘制髓鞘对水扩散的影响图。使用对特定髓鞘成分（特别是髓鞘碱性蛋白）具有高亲和力的放射性分子进行 PET 髓鞘成像。这篇综述旨在概述各种髓鞘成像技术、它们的生物物理原理、图像采集、数据分析及其验证状态。
