Xia Y, Farquhar T, Burton-Wurster N, Lust G
Department of Physics, Oakland University, Rochester, MI 48309, USA.
J Magn Reson Imaging. 1997 Sep-Oct;7(5):887-94. doi: 10.1002/jmri.1880070518.
To understand the origin of the laminated appearance of cartilage in MRI (the magic angle effect), microscopic MRI (mu MRI) experiments were performed at 14-microns pixel resolution on normal canine articular cartilage from the shoulder joints. Two-dimensional images of the spin-spin relaxation time (T2) of the cartilage-bone plug at two angles (0 degree and 55 degrees) were calculated quantitatively. A distinct T2 anisotropy was observed as a function of the cartilage tissue depth. The surface and the deep regions exhibit strong orientational dependence of T2, whereas the upper-middle region exhibits little orientational dependence of T2. These three mu MRI regions correspond approximately to the three histologic zones in cartilage tissue. The results from the bulk T2 measurements agreed with these mu MRI results. Our studies show that the laminated appearance of cartilage in MRI is caused by T2 anisotropy of the tissue. We further suggest that the molecular origin of the T2 anisotropy is the nuclear dipolar interaction. The structure of the cartilage tissue indicates that the collagen meshwork defines this T2 anisotropy. The results show that the T2 anisotropy provides an indirect but sensitive indicator for the orientation of macromolecular structures in cartilage. The clinical implications of this anisotropy are discussed.
为了解磁共振成像（MRI）中软骨分层外观的起源（魔角效应），我们以14微米像素分辨率对来自肩关节的正常犬关节软骨进行了显微MRI（μMRI）实验。定量计算了软骨-骨栓在两个角度（0度和55度）下的自旋-自旋弛豫时间（T2）的二维图像。观察到T2随软骨组织深度呈现明显的各向异性。表面和深部区域表现出强烈的T2取向依赖性，而中上部区域表现出较弱的T2取向依赖性。这三个μMRI区域大致对应于软骨组织中的三个组织学区域。整体T2测量结果与这些μMRI结果一致。我们的研究表明，MRI中软骨的分层外观是由组织的T2各向异性引起的。我们进一步认为，T2各向异性的分子起源是核偶极相互作用。软骨组织的结构表明，胶原网络决定了这种T2各向异性。结果表明，T2各向异性为软骨中大分子结构的取向提供了一个间接但敏感的指标。讨论了这种各向异性的临床意义。
