• Dimitri A Kessler, James W MacKay, Scott McDonald, Stephen McDonnell, Andrew J Grainger, Alexandra R Roberts, Robert L Janiczek, Martin J Graves, Joshua D Kaggie, and Fiona J Gilbert.
• Department of Radiology, University of Cambridge, UK.
• J Magn Reson Imaging. 2020 Dec 1; 52 (6): 1753-1764.

BackgroundDetermining the compositional response of articular cartilage to dynamic joint-loading using MRI may be a more sensitive assessment of cartilage status than conventional static imaging. However, distinguishing the effects of joint-loading vs. inherent measurement variability remains difficult, as the repeatability of these quantitative methods is often not assessed or reported.PurposeTo assess exercise-induced changes in femoral, tibial, and patellar articular cartilage composition and compare these against measurement repeatability.Study TypeProspective observational study.PopulationPhantom and 19 healthy participants.Field Strength/Sequence3T; 3D fat-saturated spoiled gradient recalled-echo; T1ρ - and T2 -prepared pseudosteady-state 3D fast spin echo.AssessmentThe intrasessional repeatability of T1ρ and T2 relaxation mapping, with and without knee repositioning between two successive measurements, was determined in 10 knees. T1ρ and T2 relaxation mapping of nine knees was performed before and at multiple timepoints after a 5-minute repeated, joint-loading stepping activity. 3D surface models were created from patellar, femoral, and tibial articular cartilage.Statistical TestsRepeatability was assessed using root-mean-squared-CV (RMS-CV). Using Bland-Altman analysis, thresholds defined as the smallest detectable difference (SDD) were determined from the repeatability data with knee repositioning.ResultsWithout knee repositioning, both surface-averaged T1ρ and T2 were very repeatable on all cartilage surfaces, with RMS-CV <1.1%. Repositioning of the knee had the greatest effect on T1ρ of patellar cartilage with the surface-averaged RMS-CV = 4.8%. While T1ρ showed the greatest response to exercise at the patellofemoral cartilage region, the largest changes in T2 were determined in the lateral femorotibial region. Following thresholding, significant (>SDD) average exercise-induced in T1ρ and T2 of femoral (-8.0% and -5.3%), lateral tibial (-6.9% and -5.9%), medial tibial (+5.8% and +2.9%), and patellar (-7.9% and +2.8%) cartilage were observed.Data ConclusionJoint-loading with a stepping activity resulted in T1ρ and T2 changes above background measurement error.Evidence Level2 TECHNICAL EFFICACY STAGE: 1 J. MAGN. RESON. IMAGING 2020;52:1753-1764.© 2020 The Authors. Journal of Magnetic Resonance Imaging published by Wiley Periodicals LLC. on behalf of International Society for Magnetic Resonance in Medicine.

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