Three-Dimensional Surface-Based Analysis of Cartilage MRI Data in Knee Osteoarthritis: Validation and Initial Clinical Application.

Background: Traditional quantitative analysis of cartilage with MRI averages measurements (eg, thickness) across regions-of-interest (ROIs) which may reduce responsiveness.

Purpose: To validate and describe clinical application of a semiautomated surface-based method for analyzing cartilage relaxation times ("composition") and morphology on MRI, 3D cartilage surface mapping (3D-CaSM).

Study Type: Validation study in cadaveric knees and prospective observational (cohort) study in human participants.

Population: Four cadaveric knees and 14 participants aged 40-60 with mild-moderate knee osteoarthritis (OA) and 6 age-matched healthy volunteers, imaged at baseline, 1, and 6 months.

Field Strength/sequence: 3D spoiled gradient echo, T rho/T magnetization-prepared 3D fast spin echo for mapping of T rho/T relaxation times and delayed gadolinium enhanced MRI of cartilage (dGEMRIC) using variable flip angle T relaxation time mapping at 3T.

Assessment: 3D-CaSM was validated against high-resolution peripheral quantitative computed tomography (HRpQCT) in cadaveric knees, with comparison to expert manual segmentation. The clinical study assessed test-retest repeatability and sensitivity to change over 6 months for cartilage thickness and relaxation times.

Statistical Tests: Bland-Altman analysis was performed for the validation study and evaluation of test-retest repeatability. Six-month changes were assessed via calculation of the percentage of each cartilage surface affected by areas of significant change (%SC), defined using thresholds based on area and smallest detectable difference (SDD).

Results: Bias and precision (0.06 ± 0.25 mm) of 3D-CaSM against reference HRpQCT data were comparable to expert manual segmentation (-0.13 ± 0.26 mm). 3D-CaSM demonstrated significant (>SDD) 6-month changes in cartilage thickness and relaxation times in both OA participants and healthy controls. The parameter demonstrating the greatest 6-month change was T relaxation time (OA median %SC [IQR] = 8.8% [5.5 to 12.6]).

Data Conclusion: This study demonstrates the construct validity and potential clinical utility of 3D-CaSM, which may offer advantages to conventional ROI-based methods.

Level Of Evidence: 2.

Technical Efficacy Stage: 2. J. Magn. Reson. Imaging 2020;52:1139-1151.