Characterization of proteoglycan depletion in articular cartilage using two-dimensional time domain nuclear magnetic resonance.

In vitro proteoglycan (PG) depletion in the 20-40% range (enzymatic PG depletion of normal cartilage in the early osteoarthritis (OA) PG depletion range) was investigated in articular cartilage using 2D time domain NMR relaxation techniques. Spin-lattice relaxation times were measured at low fields (T(1rho)) and at high fields (T(1)) using nonselective and selective excitation pulse sequences. The short relaxation time magnetization components in T(1rho) ( approximately 8% signal) and nonselective T(1) ( approximately 5% signal) experiments were significantly altered with PG degradation. In addition, a magnetization component ( approximately 5% signal) with a "fast " T(1) approximately 7 ms was observed in the T(1) experiment involving selective excitation. This fast T(1) was at least 10 times shorter than the short T(1) in the nonselective experiment and was associated with a strong magnetization exchange mechanism between collagen and PG. The results suggest that T(1rho) and T(1) (nonselective and selective) relaxation based MRI techniques, which focus on the short relaxation time magnetization components, have the potential of detecting molecular abnormalities associated with early OA earlier than single, long relaxation time component approaches.