Changes in Proton Dynamics in Articular Cartilage Caused by Phosphate Salts and Fixation Solutions

The objective was to study the effect of phosphate salts and fixation solutions on the proton dynamics in articular cartilage in vitro. Microscopic magnetic resonance imaging (µMRI) T(2) anisotropy and nuclear magnetic resonance (NMR) double quantum–filtered (DQF) spectroscopy were used to study the full-thickness articular cartilage from several canine humeral heads. The in-plane pixel size across the depth of the cartilage tissue was 13 µm. The acid phosphate salt was an effective exchange catalyst for proton exchange in the cartilage with an organized structure of collagen fibrils, while the alkaline phosphate salt was not. For cartilage tissue containing less organized collagen fibrils, both acid and alkaline phosphate salts have no significant effect on the T(2) value at low concentration but decrease the T(2) value at high concentration. The solutions of NaCl, KCl, CaCl(2), and D-PBS were found to have no significant effect on T(2) and DQF in cartilage. This study demonstrates the ability to modify the proton exchange in articular cartilage using the solutions of phosphate salts. The ability to modify the proton exchange in articular cartilage can be used to modulate the laminar appearance of articular cartilage in MRI.