T1ρ relaxation can assess longitudinal proteoglycan loss from articular cartilage in vitro

Objective: To assess the correlation between changes in spin-lattice relaxation in the rotating frame (TIP) and proteoglycan (PG) loss from bovine articular cartilage and to demonstrate the feasibility of performing T-1P MR imaging on a 1.5T clinical scanner. Design: MR relaxation times (T-1rho, T-2 and T-1) were measured from excised cartilage plugs (N=3) before and after two sequential digestions with trypsin on a 2T whole-body magnet. Proteoglycan and collagen loss induced by the trypsin digestion was measured using standard biochemical techniques. The correlation between changes in relaxation times and PG loss were tested with regression analysis. T-1rho MRI was also performed on a clinical 1.5T MRI system to determine whether the spatial distribution of PG loss could be detected. The MRI results were compared with histology sections of native and PG-depleted tissue. Results: Increase in T-1rho relaxation times correlated with PG loss (R-2=0.81). T-1rho measurements alone were indicative of PG loss (R-2=0.8), the addition of T1 and T2 data into the statistical model did not improve the correlation substantially (R-2= 0.83). T-1rho-weighted imaging demonstrated a hyperintense lamina at the articular surface of the digested tissue, which was subjected to trypsin digestion that correlated with a superficial zone of PG loss observed on histological sections. Conclusion: The results of this study demonstrate that T-1rho relaxation changes are correlated with PG loss in vitro. Furthermore, T-1rho measurements alone can be used to indicate PG loss data. T-1rho MRI may thus be developed into a useful adjunct to existing techniques for the evaluation of cartilage disease. (C) 2002 OsteoArthritis Research Society International. Published by Elsevier Science Ltd. All rights reserved.