Qazi A A, Folkesson J, Pettersen P C, Karsdal M A, Christiansen C, Dam E B
Image Group, University of Copenhagen, Denmark.
Osteoarthritis Cartilage. 2007 Oct;15(10):1199-206. doi: 10.1016/j.joca.2007.03.016. Epub 2007 May 10.
Cartilage loss as determined either by magnetic resonance imaging (MRI) or by joint space narrowing in X-rays is the result of cartilage erosion. However, metabolic processes within the cartilage that later result in cartilage loss may be a more accurate assessment method for early changes. Early biological processes of cartilage destruction are among other things, a combination of proteoglycan turnover, as a result of altered charge distributions, and local alterations in water content (edema). As water distribution is detectable by MRI, the aim of this study was to investigate cartilage homogeneity visualized by MRI related to water distribution, as a potential very early marker for early detection of knee osteoarthritis (OA).
One hundred and fourteen right and left knees from 71 subjects aged 22-79 years were scanned using a Turbo 3D T(1) sequence on a 0.18T MRI Esaote scanner. The medial compartment of the tibial cartilage sheet was segmented using a fully automatic voxel classification scheme based on supervised learning. From the segmented cartilage sheet, homogeneity was quantified by measuring entropy from the distribution of signal intensities inside the compartment. For each knee an X-ray was acquired and the knees were categorized by the Kellgren and Lawrence (KL) index and the joint space width (JSW) was measured. The P-values for separating the groups by each of JSW, cartilage volume, cartilage mean intensity, and cartilage homogeneity were calculated using the unpaired t-test.
The P-value for separating the group diagnosed as KL 0 from the group being KL 1 based on JSW, volume and mean signal intensity the values were P=0.9, P=0.4 and P=0.0009, respectively. In contrast, the P-value for homogeneity was P=0.0004. The precision of the measures assessed, as a test-retest root mean square coefficient of variation (RMS-CV%) was 3.9% for JSW, 7.4% for volume, 3.9% for mean signal intensity and 3.0% for homogeneity quantification.
These data demonstrate that the distribution of components of the articular matrix precedes erosion, as measured by cartilage homogeneity related to water concentration. We show that homogeneity was able to separate early OA from healthy individuals in contrast to traditional volume and JSW quantifications. These data suggest that cartilage homogeneity quantification may be able to quantify early biochemical changes in articular cartilage prior to cartilage loss and thereby provide better identification of patients for OA trials who may respond better to medicinal intervention of some treatments. In addition, this study supports the feasibility of using low-field MRI in clinical studies.
通过磁共振成像（MRI）或X线关节间隙变窄所确定的软骨损伤是软骨侵蚀的结果。然而，软骨内随后导致软骨损伤的代谢过程可能是早期变化的更准确评估方法。软骨破坏的早期生物学过程包括蛋白聚糖周转率的变化（由于电荷分布改变）以及局部含水量变化（水肿）等。由于MRI可检测到水分分布，本研究旨在探讨与水分分布相关的MRI显示的软骨同质性，作为早期检测膝关节骨关节炎（OA）的潜在非常早期的标志物。
对71名年龄在22 - 79岁的受试者的114个左右膝关节，使用0.18T MRI Esaote扫描仪上的Turbo 3D T(1)序列进行扫描。基于监督学习，使用全自动体素分类方案对胫骨软骨板的内侧部分进行分割。从分割的软骨板中，通过测量区域内信号强度分布的熵来量化同质性。对每个膝关节进行X线检查，并根据Kellgren和Lawrence（KL）指数对膝关节进行分类，测量关节间隙宽度（JSW）。使用不成对t检验计算通过JSW、软骨体积、软骨平均强度和软骨同质性对各组进行区分的P值。
基于JSW、体积和平均信号强度将诊断为KL 0的组与KL 1的组区分开的P值分别为P = 0.9、P = 0.4和P = 0.0009。相比之下，同质性的P值为P = 0.0004。所评估测量的精度，作为重测均方根变异系数（RMS - CV%），JSW为3.9%，体积为7.4%，平均信号强度为3.9%，同质性量化为3.0%。
这些数据表明，与水浓度相关的软骨同质性所测量的关节基质成分分布先于侵蚀。我们表明，与传统的体积和JSW量化相比，同质性能够将早期OA与健康个体区分开来。这些数据表明，软骨同质性量化可能能够在软骨损伤之前量化关节软骨的早期生化变化，从而更好地识别可能对某些治疗的药物干预反应更好的OA试验患者。此外，本研究支持在临床研究中使用低场MRI的可行性。
