Knee Cartilage Quantification: Performance of Low-Field MR in Detecting Low Grades of Chondropathy

This study aimed to evaluate the diagnostic accuracy of T2 mapping on low-field (0.31 T) MRI for detecting low-grade knee chondropathy, using arthroscopy as the reference standard. Fifty-two patients (mean age 48.1 ± 17.2 years) undergoing arthroscopy for anterior cruciate ligament or meniscal tears were prospectively enrolled, excluding those with previous surgery, infection, or high-grade chondropathy (Outerbridge III-IV). MRI was performed with a 0.31 T scanner using a 3D SHARC sequence, and T2 relaxometric maps were generated for 14 cartilage regions per knee according to the WORMS classification. Arthroscopy, performed within one month by two blinded surgeons, served as the gold standard. A total of 728 regions were analyzed. T2 mapping differentiated healthy cartilage (grade 0) from early chondropathy (grades I-II) with an optimal cut-off of 45 ms and moderate discriminative accuracy (AUC = 0.714 for Reader 1 and 0.709 for Reader 2). Agreement with arthroscopy was good (κ = 0.731), with excellent intra-reader (ICC = 0.998) and good inter-reader reproducibility (ICC = 0.753). Most degenerative changes were located at the femoral condyles (59%). Low-field T2 mapping showed good diagnostic performance and reproducibility in detecting early cartilage degeneration, supporting its potential as a cost-effective and accessible quantitative biomarker for the assessment of cartilage integrity in clinical practice.