Quantitative assessment of cartilage status in osteoarthritis by quantitative magnetic resonance imaging: Technical validation for use in analysis of cartilage volume and further morphologic parameters

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Abstract
Objective Quantitative diagnostic tools for osteoarthritis (OA) are important for evaluating the treatment response to structure‐modifying drugs. This study was undertaken to test the technical validity (accuracy) of quantitative magnetic resonance imaging (qMRI) for reliable determination of the total bone interface area, percentage of cartilaginous (denuded) joint surface area, and cartilage thickness in OA. Methods High‐resolution MRIs of femorotibial and patellar cartilage were acquired in 21 patients prior to total knee arthroplasty, using a T1‐weighted gradient‐echo sequence with water excitation. After segmentation of original bone interface areas (before disease onset) and the actual cartilage layer, the percentages of cartilaginous joint surface area, cartilage thickness, and cartilage volume were determined using proprietary software. During surgery, the patella and the medial and lateral tibia were resected. Results obtained with qMRI were compared with those obtained by direct image analysis of surface area, cartilage thickness, and cartilage volume of the surgically removed tissue. Results Pairwise differences between results obtained with qMRI and morphologic analysis were ±4.6% for percentage of cartilaginous surface area, ±8.9% for cartilage thickness, and ±9.1% for cartilage volume. Correlation coefficients ranged from 0.92 (thickness) to 0.98 (volume). Conclusion Quantitative MRI permits technically accurate and differential assessment of increases in eroded joint surface area and reductions in cartilage thickness in OA. The surrogate validity of these parameters requires testing in longitudinal studies. These parameters may be advantageous over determination of cartilage volume alone when diagnosing OA, exploring its progression, or testing responsiveness to new therapies.