Dynamic contrast-enhanced magnetic resonance imaging of the synovium and synovial subregions in knee osteoarthritis: test-retest repeatability.

Background: Quantitative dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) can potentially be used to assess synovial inflammation in patients with knee osteoarthritis (OA). Precise methods are needed for adequate identification of changes in clinical trials. In this study, we aimed to evaluate test-retest repeatability of DCE-MRI within the synovium of patients with knee OA, and develop a semi-automatic method for synovial subregion assessment. Methods: In this secondary explorative analysis, we included 31 adults with radiographically confirmed mild to moderate knee OA receiving sham treatment as participants of a randomized controlled trial evaluating genicular artery embolization. DCE-MRI of the knee was performed at baseline and at 1-month follow-up. The synovium was semi-automatically segmented and subdivided in 8 subregions based on blood vessel mapping. Quantitative DCE-MRI parameters were extracted from the synovium and its subregions by voxel-wise pharmacokinetic modeling. A two-way random effects model was used to estimate within-subject variance and between-subject variance, and intraclass correlation (ICC), within-subject standard deviation or coefficient of variation, and the repeatability coefficient (RC) were calculated. Results: DCE-MRI parameter Ktrans showed good repeatability with an ICC of 0.84 and a RC of 0.039. Semi-quantitative parameter IAUC60 showed a similar ICC of 0.85 and a slightly higher RC of 0.090. For subregional assessment, ICCs for Ktrans ranged between 0.70 and 0.89 while RCs ranged between 0.028 and 0.099. Conclusions: Quantitative DCE-MRI biomarkers have good test-retest repeatability on both the whole synovium and synovial subregions, with Ktrans showing the best performance.