Fachgebiet Technische Physik II/Polymerphysik, Institute of Physics, Technische Universität Ilmenau, PO Box 100 565, 98684 Ilmenau, Germany.
J Magn Reson. 2011 Dec;213(1):112-8. doi: 10.1016/j.jmr.2011.09.014. Epub 2011 Sep 10.
The structure of articular cartilage is separated into three layers of differently oriented collagen fibers, which is accompanied by a gradient of increasing glycosaminoglycan (GAG) and decreasing water concentration from the top layer towards the bone interface. The combined effect of these structural variations results in a change of the longitudinal and transverse relaxation times as a function of the distance from the cartilage surface. In this paper, this dependence is investigated at a magnetic field strength of 0.27 T with a one-dimensional depth resolution of 50 μm on bovine hip and stifle joint articular cartilage. By employing this method, advantage is taken of the increasing contrast of the longitudinal relaxation rate found at lower magnetic field strengths. Furthermore, evidence for an orientational dependence of relaxation times with respect to an axis normal to the surface plane is given, an observation that has recently been reported using high-field MRI and that was explained by preferential orientations of collagen bundles in each of the three cartilage zones. In order to quantify the extent of a further contrast mechanism and to estimate spatially dependent glycosaminoglycan concentrations, the data are supplemented by proton relaxation times that were acquired in bovine articular cartilage that was soaked in a 0.8 mM aqueous Gd++ solution.
关节软骨的结构分为三层不同取向的胶原纤维，这伴随着糖胺聚糖（GAG）的梯度增加和水浓度从顶层向骨界面逐渐降低。这些结构变化的综合作用导致了纵向和横向弛豫时间随距离软骨表面的变化。在本文中，在磁场强度为 0.27 T 的情况下，对牛髋关节和膝关节关节软骨进行了一维深度分辨率为 50 μm 的研究。通过采用这种方法，可以利用在较低磁场强度下发现的纵向弛豫率增加的对比度。此外，还给出了关于垂直于表面平面的轴的弛豫时间的取向依赖性的证据，这一观察结果最近使用高磁场 MRI 进行了报道，并通过三个软骨区中每个区的胶原束的优先取向进行了解释。为了量化进一步对比机制的程度并估计空间相关的糖胺聚糖浓度，通过在含有 0.8 mM 水溶液 Gd++溶液中浸泡的牛关节软骨中获取的质子弛豫时间来补充数据。
