Intrarater and Interrater Reliability of the Quantification of Knee Cartilage MR Relaxation Metrics

Background Magnetic resonance (MR) imaging is often used to study osteoarthritis (OA), as advanced MR imaging methods can provide a quantitative assessment of tissue biochemistry or composition. For example, the magnetic relaxation times T _1ρ (i.e., 1/R _1ρ ) and T ₂ (i.e., 1/R ₂ ) of water molecules within articular cartilage have been demonstrated to be imaging biomarkers sensitive to the compositional changes associated with early OA. However, the outcome of MR imaging data analysis depends on relaxation data acquisition methods as well as assessor variability if manual segmentation is performed. Therefore, the goal of the current study was to evaluate the intra- and interrater reliability of established imaging protocols for performing quantitative cartilage MR relaxation metrics of the knee joint. Methods Right knee MR images were obtained from five healthy individuals (average age, 24.4 years; 3 females) via a 3.0T MRI scanner equipped with a 16-channel knee T/R coil. A double echo steady state (DESS) sequence was used for anatomical imaging, and the established MAPSS sequences were used for R _1ρ and R ₂ mapping. One assessor performed manual segmentations of the knee cartilage on two separate occasions, whereas a second assessor performed segmentations once. Both the R _1ρ and R ₂ mean values were then calculated for the tibial, patellar, femoral trochlear, central femoral condylar, and posterior femoral condylar cartilages. Intraclass correlation coefficients [ICC (3,1)] and ICCs (2,1) were used to evaluate intra- and interrater reliability, respectively. The standard error of measurement (SEM) was used to assess absolute reliability. Results The intrarater knee cartilage relaxation metrics demonstrated good to excellent reliability, ranging between 0.88 and 0.99, with SEMs ranging between 0.16 and 0.80. The interrater reliability similarly ranged from 0.79–0.97, with SEMs ranging between 0.27 and 1.10. Conclusions Manual segmentation of specific MR slices and known subregions is highly reliable and repeatable for the quantification of cartilage MR relaxation metrics. This validation paves the way for the large-scale application of this method in prospective trials that longitudinally monitor OA development and progression in the knee joint.