Their article, ‘Effectively Measuring Exercise–related Variations in T1ρ and T2 Relaxation Times of Healthy Articular Cartilage’ is currently in press and assesses exercise-induced changes in femoral, tibial and patellar articular cartilage composition and compares these against measurement repeatability.
Background: Determining the compositional response of articular cartilage to dynamic joint loading using magnetic resonance imaging may be a more sensitive assessment of cartilage status than conventional static imaging. However, distinguishing the effects of joint loading versus 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; T1ρ- and T2-prepared pseudo-steady-state 3D fast spin echo. Assessment: The intra-sessional 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 time points after a 5-minute repeated, joint-loading stepping activity. Three-dimensional 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 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 Conclusion: Joint loading with a stepping activity resulted in T1ρ and T2 changes above background measurement error.
Key Words: Articular Cartilage; MRI; Quantitative Imaging; Repeatability; Exercise; Relaxation Time
The Journal of Magnetic Resonance Imaging is an international journal devoted to the timely publication of basic and clinical research, educational and review articles, and other information related to the diagnostic applications of magnetic resonance.