Comparison of 3D Quantitative Osteoarthritis Imaging Biomarkers from Paired CT and MR Images: data from the IMI-APPROACH study

Introduction: MRI bone surface area and femoral bone shape (B-score) measures have been employed as quantitative endpoints in DMOAD clinical trials. Computerized Tomography (CT) imaging is more commonly used for 3D visualization of bony anatomy due to its high bone-soft tissue contrast. We aimed to compare CT and MRI assessments of 3D imaging biomarkers. Methods: : We used baseline and 24-month image data from the IMI-APPROACH 2-year prospective cohort study. Femur and tibia were automatically segmented using active appearance models to measure 3D bone shape, area and 3D joint space width (3DJSW). Linear regression was used to test for correlation between measures. Limits of agreement and bias were tested using Bland-Altman analysis. Results: : CT-MR pairs of the same knee were available from 434 participants (78% female). B-scores from CT and MR were strongly correlated (R 2 = 0.938) with minimal bias of 0.1. Area measures were also correlated but showed a consistent bias (MR smaller). 3DJSW showed different bias (MR larger) in lateral and medial sides. Discussion: The strong correlation and small B-score bias suggests that B-score may be measured reliably using either modality. It is likely that the bone surface identified using MR and CT will be at slightly different positions within the bone/cartilage boundary. The negative bone area bias suggests the MR bone boundary is inside the CT boundary producing smaller areas for MR, consistent with the positive 3DJSW bias. The lateral-medial 3DJSW difference is possibly due to a difference in knee pose during acquisition (fully extended for CT, flexed for MR). Trial registration number: NCT03883568