T mapping of healthy knee cartilage: multicenter multivendor reproducibility.

Background: T mapping is increasingly used to quantify cartilage degeneration in knee osteoarthritis (OA), yet reproducibility studies in a multicenter setting are limited. The purpose of this study was to determine the longitudinal reproducibility and multicenter variation of cartilage T mapping, using various MRI equipment and acquisition protocols.

Methods: In this prospective multicenter study, four traveling, healthy human subjects underwent T mapping twice at five different centers with a 6-month-interval. Centers had various MRI scanners, field strengths, and T mapping acquisition protocols. Mean T values were calculated in six cartilage regions of interest (ROIs) as well as an average value per patient. A phantom was scanned once at each center. To evaluate longitudinal reproducibility, intraclass correlation coefficients (ICC), root-mean-square coefficient of variation (RMS-CV), and a Bland-Altman plot were used. To assess the variation of and phantom T values across centers, ANOVA was performed.

Results: ICCs of the T mapping measurements per ROI and the ROI's combined ranged from 0.73 to 0.91, indicating good to excellent longitudinal reproducibility. RMS-CVs ranged from 1.1% to 1.5% (per ROI) and 0.6% to 1.6% (ROIs combined) across the centers. A Bland-Altman plot did not reveal a systematic error. Evident, but consistent, discrepancies in T values were observed across centers, both and in the phantom.

Conclusions: The results of this study suggest that T mapping can be used to longitudinal assess cartilage degeneration in multicenter studies. Given the differences in absolute cartilage T values across centers, absolute T values derived from various centers in multicenter multivendor trials should not be pooled.