Effectively Measuring Exercise‐Related Variations in T1ρ and <scp>T2</scp> Relaxation Times of Healthy Articular Cartilage
Dimitri A. Kessler, James Mackay, Scott D. McDonald, Stephen McDonnell, Andrew J. Grainger, Alexandra R. Roberts, Robert L. Janiczek, Martin J. Graves, Joshua Kaggie, Fiona J. Gilbert
Abstract
Background Determining 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. Purpose To assess exercise‐induced changes in femoral, tibial, and patellar articular cartilage composition and compare these against measurement repeatability. Study Type Prospective observational study. Population Phantom and 19 healthy participants. Field Strength/Sequence 3T; 3D fat‐saturated spoiled gradient recalled‐echo; T 1ρ ‐ and T 2 ‐prepared pseudosteady‐state 3D fast spin echo. Assessment The intrasessional repeatability of T 1ρ and T 2 relaxation mapping, with and without knee repositioning between two successive measurements, was determined in 10 knees. T 1ρ and T 2 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 Tests Repeatability 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. Results Without knee repositioning, both surface‐averaged T 1ρ and T 2 were very repeatable on all cartilage surfaces, with RMS‐CV <1.1%. Repositioning of the knee had the greatest effect on T 1ρ of patellar cartilage with the surface‐averaged RMS‐CV = 4.8%. While T 1ρ showed the greatest response to exercise at the patellofemoral cartilage region, the largest changes in T 2 were determined in the lateral femorotibial region. Following thresholding, significant (>SDD) average exercise‐induced in T 1ρ and T 2 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 Conclusion Joint‐loading with a stepping activity resulted in T 1ρ and T 2 changes above background measurement error. Evidence Level 2 Technical Efficacy Stage 1 J. MAGN. RESON. IMAGING 2020;52:1753–1764.