Department of Applied Physics, University of Eastern Finland, POB 1627, FI-70211, Kuopio, Finland.
Research Unit of Medical Imaging, Physics and Technology, University of Oulu, POB 5000, FI-90014, Oulu, Finland.
Sci Rep. 2017 Aug 29;7(1):9606. doi: 10.1038/s41598-017-10053-2.
In highly organized tissues, such as cartilage, tendons and white matter, several quantitative MRI parameters exhibit dependence on the orientation of the tissue constituents with respect to the main imaging magnetic field (B). In this study, we investigated the dependence of multiple relaxation parameters on the orientation of articular cartilage specimens in the B. Bovine patellar cartilage-bone samples (n = 4) were investigated ex vivo at 9.4 Tesla at seven different orientations, and the MRI results were compared with polarized light microscopy findings on specimen structure. Dependences of T and continuous wave (CW)-T relaxation times on cartilage orientation were confirmed. T (and T*) had the highest sensitivity to orientation, followed by T and adiabatic T. The highest dependence was seen in the highly organized deep cartilage and the smallest in the least organized transitional layer. Increasing spin-lock amplitude decreased the orientation dependence of CW-T. T was found practically orientation-independent and was closely followed by adiabatic T. The results suggest that T and adiabatic T should be preferred for orientation-independent quantitative assessment of organized tissues such as articular cartilage. On the other hand, based on the literature, parameters with higher orientation anisotropy appear to be more sensitive to degenerative changes in cartilage.
在高度有序的组织中,如软骨、肌腱和白质,几个定量 MRI 参数表现出对组织成分相对于主成像磁场 (B) 方向的依赖性。在这项研究中,我们研究了多个弛豫参数对关节软骨标本在 B 中的方向的依赖性。在 9.4T 下对 4 个牛髌软骨-骨样本进行了离体研究,在七个不同的方向上进行了研究,并且将 MRI 结果与样本结构的偏光显微镜发现进行了比较。证实了 T 和连续波 (CW)-T 弛豫时间对软骨方向的依赖性。T(和 T*)对方向的敏感性最高,其次是 T 和绝热 T。在高度有序的深层软骨中观察到最高的依赖性,在最不有序的过渡层中观察到最小的依赖性。增加自旋锁定幅度会降低 CW-T 的方向依赖性。发现 T 实际上是与方向无关的,并且与绝热 T 密切相关。结果表明,T 和绝热 T 应该优先用于关节软骨等组织的与方向无关的定量评估。另一方面,根据文献,具有更高各向异性的参数似乎对软骨的退行性变化更敏感。