Thompson Garth John, Wang Ziyi, Kim Jae-Yoon, Li Hui, Kim Dong-Hyun, Ye Qiong, Su Min-Ying
Human Institute, ShanghaiTech University, Shanghai, China.
School of Life Science and Technology, ShanghaiTech University, Shanghai, China.
NMR Biomed. 2025 Jan;38(1):e5303. doi: 10.1002/nbm.5303.
Myelin is essential in the nervous system of mammals. As the location and degree of myelin loss can reflect varied pathophysiological status, noninvasive measurement of myelin is of high importance. The magnetic resonance imaging (MRI) technique of myelin water fraction (MWF) derived from multi-echo gradient echo (MGRE) sequence is a promising tool for the quantification of myelin content due to the low specific absorption rate (SAR) compared with the spin-echo sequence, time efficiency, and wide availability. Yet to our knowledge, MGRE-derived MWF has never been quantitatively validated with histology. The main objective of this study was to quantitatively validate the MRI findings by referencing the myelin histology using a rat model. As a second objective, we investigated how the orientation of white matter fibers with respect to the static B field impacted both the apparent transverse relaxation rate (R* = 1/T*) and the derived MWF. Moreover, MWF is known to change with age; thus, we compared rat brains of different ages. The orientation effect of MWF in a clinical setting was studied using 3 T human data. Twenty ex vivo rat brains with different ages and three healthy volunteers were scanned on a 9.4 T Bruker and 3.0 T Siemens systems, respectively. The 3D MGRE and diffusion tensor imaging (DTI) data were acquired. Our results showed a highly significant correlation between MGRE-derived MWF and histological stain of myelin, and susceptibility and diffusivity also demonstrated a significant association with myelin. Both MWF and R* (R* = 1/T*) values changed as a function of orientation, and the function varied with age. Furthermore, MWF and R* were more sensitive to age than DTI. In vivo 3 T human MWF also changed substantially with the orientation as well. Our results support that MGRE-derived MWF can be used to assess the myelin content quantitatively.
髓磷脂在哺乳动物的神经系统中至关重要。由于髓磷脂损失的位置和程度能够反映不同的病理生理状态，因此对髓磷脂进行无创测量具有高度重要性。源自多回波梯度回波（MGRE）序列的髓磷脂水含量（MWF）磁共振成像（MRI）技术，因其与自旋回波序列相比具有低比吸收率（SAR）、时间效率高以及广泛可用性等特点，是一种用于量化髓磷脂含量的有前景的工具。然而据我们所知，源自MGRE的MWF从未通过组织学进行过定量验证。本研究的主要目的是通过使用大鼠模型参考髓磷脂组织学来定量验证MRI结果。作为第二个目的，我们研究了白质纤维相对于静态B场的方向如何影响表观横向弛豫率（R* = 1/T*）以及衍生的MWF。此外，已知MWF会随年龄变化；因此，我们比较了不同年龄的大鼠脑。使用3T人体数据研究了临床环境中MWF的方向效应。分别在9.4T布鲁克和3.0T西门子系统上扫描了20个不同年龄的离体大鼠脑和3名健康志愿者。获取了3D MGRE和扩散张量成像（DTI）数据。我们的结果表明，源自MGRE的MWF与髓磷脂的组织学染色之间存在高度显著的相关性，并且磁化率和扩散率也与髓磷脂表现出显著关联。MWF和R*（R* = 1/T*）值均随方向而变化，且该函数随年龄而异。此外，MWF和R*对年龄的敏感性高于DTI。体内3T人体MWF也随方向发生了显著变化。我们的结果支持源自MGRE的MWF可用于定量评估髓磷脂含量。
