T2 mapping of healthy knee cartilage: multicenter multivendor reproducibility

Abstract

Background: T₂ 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 T₂ mapping, using various MRI equipment and acquisition protocols.

Methods: In this prospective multicenter study, four traveling, healthy human subjects underwent T₂ mapping twice at five different centers with a 6-month-interval. Centers had various MRI scanners, field strengths, and T₂ mapping acquisition protocols. Mean T₂ 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 in vivo and phantom T₂ values across centers, ANOVA was performed.

Results: ICCs of the T₂ 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 T₂ values were observed across centers, both in vivo and in the phantom.

Conclusions: The results of this study suggest that T₂ mapping can be used to longitudinal assess cartilage degeneration in multicenter studies. Given the differences in absolute cartilage T₂ values across centers, absolute T₂ values derived from various centers in multicenter multivendor trials should not be pooled.

Keywords: Knee; T2 mapping; cartilage; magnetic resonance imaging (MRI); reproducibility.

Figure 1

Cartilage segmentation on sagittal high-resolution FSPGR image, lateral compartment. Blue dotted lines surround the segmented mask; white boxes represent the ROIs. Fem_post, posterior femoral condyle; Fem_wb, weight-bearing femoral condyle; Plat_wb, weight-bearing tibial plateau.

Figure 2

Bland-Altman plot showing the differences in in vivo T₂ values between baseline and follow-up against the mean T₂ values plotted per cartilage ROI for each subject. Each colored shape represents the four subjects with each six ROIs. The bold line represents the mean difference, dotted lines represent the limits of agreement.

Figure 3

Average T₂ values of subjects and phantom vials per center. (A) Baseline average T₂ values per subject in each center; (B) Phantom T₂ values plotted per vial in each center. The concentration of manganese chloride for each vial was: vial 1 =0%, vial 2 =5%, vial 3 =10%, vial 4 =15%, vial 5 =20%, vial 6 =30%, vial 7 =50%, and vial 8 =80%.