Evaluation of Internal Structure of the Articular Cartilage in Terms of ^1H-NMR Relaxation Behavior

用快速反转恢复和多自旋回波磁共振成像（MRI）测量关节软骨的^1H-纵向（T_1）和横向（T_2）弛豫时间，分析关节软骨的结构特征。从15个股骨内侧髁上解剖出来自承重和非承重区域的成对软骨-骨栓，并在有和没有静态载荷（0.15-1.0 MPa）的情况下进行NMR测量。无负荷时软骨的T_1值在关节面正下方最大，向深层逐渐减小。同一软骨的T_2在关节面或关节面正下方有一最大值，向中间区迅速下降，向最深区又上升。负重区最深区T_2的增加比非负重区显著。这些T_1和T_2的层间差异可以解释关节软骨在MR图像上的层状表现。在静态载荷下，过渡区（从关节面正下方到中间区）T_1明显降低。由于T_1与含水量呈正相关，T_1的降低可能意味着最大的水分损失发生在过渡区。这些结果表明，过渡区可能会减弱关节中的机械应力，并且从软骨中挤出的水可以显著地有助于关节的润滑。

The structural characteristics of articular cartilage were analyzed usnig ^1H-longitudinal (T_1) and transverse (T_2) relaxation times as measured by fast-inversion-recovery and multi-spin-echo magnetic resonance imaging(MRI). Pairs of cartilage-bone plugs from weight bearing and non-weight bearing regions were dissected from 15 medial femoral condyles and were subjected to NMR measurements with and without static loads (0.15-1.0 MPa). The T_1 of the cartilage with no load showed a maximum value just beneath the articular surface and this value decreased gradually towards the deeper zones. The T_2 of the same cartilage showed a maximum value at or just beneath the articular surface which decreased rapidly towards the intermediate zone yet increased again in the deepest zone. The increase of T_2 in the deepest zone was more greatly pronounced in the weight bearing region than in the non-weight bearing region. These layer-dependent differences in the T_1 and T_2 could account for the laminar appearance of the articular cartilage in the MR images. Under static loads, the decrease of T_1 in the transitional zone (from just beneath the articular surface to the intermidiate zone) was significant. Because the T_1 has a positive correlation with the water content, this decrease of T_1 might signify that the largest water loss occurs in the transitional zone. These results suggest that the transitional zone might be attenuating the mechanical stress in the joint, and the expressed water from the cartilage could substantially contribute to the lubrication of the joint.