eScience Center, University of Copenhagen, Copenhagen, Denmark.
IEEE Trans Med Imaging. 2012 Jul;31(7):1404-12. doi: 10.1109/TMI.2012.2191813. Epub 2012 Mar 23.
We present methods to quantify the medial tibio- femoral (MTF) joint contact area (CA) and congruity index (CI) from low-field magnetic resonance imaging (MRI). Firstly, based on the segmented MTF cartilage compartments, we computed the contact area using the Euclidian distance transformation. The CA was defined as the area of the tibial superior surface and the femoral inferior surface that are less than a voxel width apart. Furthermore, the CI is computed point-by-point by assessing the first- and second-order general surface features over the contact area. Mathematically, it is the inverse distance between the local normal vectors (first-order features) scaled by the local normal curvatures (second-order features) along the local direction of principal knee motion in a local reference coordinate system formed by the directions of principal curvature and the surface normal vector. The abilities of the CA and the CI for diagnosing osteoarthritis (OA) at different levels (disease severity was assessed using the Kellgren and Lawrence Index, KL) were cross-validated on 288 knees at baseline. Longitudinal analysis was performed on 245 knees. The precision quantified on 31 scan-rescan pairs (RMS CV) for CA was 13.7% and for CI 7.5%. The CA increased with onset of the disease and then decreased with OA progression. The CI was highest in healthy and decreased with the onset of OA and further with disease progression. The CI showed an AUC of 0.69 (p < 0.0001) for separating KL = 0 and KL > 0. For separating KL < 1 or KL = 1 and KL > 1 knees, the AUC for CI was 0.73 (p < 0.0001). The CA demonstrated longitudinal responsiveness (SRM) at all stages of OA, whereas the CI did for advanced OA only. Eventually, the quantified CA and the CI might be suitable to help explaining OA onset, diagnosis of (early) OA, and measuring the efficacy of DMOADs in clinical trials.
我们提出了从低场磁共振成像（MRI）量化内侧胫股（MTF）关节接触面积（CA）和一致性指数（CI）的方法。首先，基于分割的 MTF 软骨隔室，我们使用欧几里得距离变换计算接触面积。CA 定义为胫骨上表面和股骨下表面之间的面积，它们之间的距离小于一个体素宽度。此外，CI 是通过评估接触区域上的一阶和二阶一般表面特征逐点计算的。从数学上讲，它是沿主膝关节运动的局部方向的局部法向量（一阶特征）的倒数，该方向由主曲率的方向和表面法向量形成局部参考坐标系。在基线处对 288 个膝关节进行交叉验证，以评估 CA 和 CI 在不同水平（使用 Kellgren 和 Lawrence 指数，KL 评估疾病严重程度）诊断骨关节炎（OA）的能力。对 245 个膝关节进行了纵向分析。在 31 个扫描-重扫对（RMS CV）上，CA 的精度为 13.7%，CI 的精度为 7.5%。CA 随着疾病的发生而增加，然后随着 OA 的进展而减少。CI 在健康膝关节中最高，随着 OA 的发生而降低，随着疾病的进展进一步降低。CI 对区分 KL = 0 和 KL > 0 的曲线下面积（AUC）为 0.69（p < 0.0001）。对于区分 KL < 1 或 KL = 1 和 KL > 1 的膝关节，CI 的 AUC 为 0.73（p < 0.0001）。CA 在 OA 的所有阶段均表现出纵向反应性（SRM），而 CI 仅在晚期 OA 时表现出这种反应性。最终，量化的 CA 和 CI 可能适合于帮助解释 OA 的发生、（早期）OA 的诊断以及在临床试验中测量 DMOAD 的疗效。
