Assessment of Low-Grade Focal Cartilage Lesions in the Knee With Sodium MRI at 7 T

Objectives Several articles have investigated potential of sodium ( 23 Na) magnetic resonance imaging (MRI) for the in vivo evaluation of cartilage health, but so far no study tested its feasibility for the evaluation of focal cartilage lesions of grade 1 or 2 as defined by the International Cartilage Repair Society. The aims of this study were to evaluate the ability of 23 Na-MRI to differentiate between early focal lesions and normal-appearing cartilage, to evaluate within-subject reproducibility of 23 Na-MRI, and to monitor longitudinal changes in participants with low-grade, focal chondral lesions. Materials and Methods Thirteen participants (mean age, 50.1 ± 10.9 years; 7 women, 6 men) with low-grade, focal cartilage lesions in the weight-bearing region of femoral cartilage were included in this prospective cohort study. Participants were assessed at baseline, 1 week, 3 months, and 6 months using morphological MRI at 3 T and 7 T, compositional 23 Na-MRI at 7 T, and the Knee Injury and Osteoarthritis Outcome Score (KOOS) questionnaire. 23 Na signal intensities corrected for coil sensitivity and partial volume effect ( 23 Na-cSI) were calculated in the lesion, and in weight-bearing and non–weight-bearing regions of healthy femoral cartilage. Coefficients of variation, repeated measures analysis of covariance models, and Pearson correlation coefficients were calculated to evaluate within-subject reproducibility as well as cross-sectional and longitudinal changes in 23 Na-cSI values. Results The mean coefficients of variation of 23 Na-cSI values between the baseline and 1-week follow-up were 5.1% or less in all cartilage regions. Significantly lower 23 Na-cSI values were observed in lesion than in weight-bearing and non–weight-bearing regions at all time points (all P values ≤ 0.002). Although a significant decrease from baseline 23 Na-cSI values in lesion was found at 3-month visit ( P = 0.015), no substantial change was observed at 6 months. KOOS scores have improved in all subscales at 3 months and 6 months visit, with a significant increase observed only in the quality of life subscale ( P = 0.004). Conclusions In vivo 23 Na-MRI is a robust and reproducible method that allows to differentiate between low-grade, focal cartilage lesions and normal-appearing articular cartilage, which supports the concept that compositional cartilage changes can be found early, before the development of advanced morphological changes visible at clinical 3-T MRI.