Sodium and proton MR properties of cartilage during compression

Proton and sodium MR relaxation times of bovine articular cartilage specime ns were measured as a function of proteoglycan (PG) depletion and as a func tion of mechanical compression. Proton and sodium relaxation times of norma l cartilage were compared with relaxation times of PG-depleted cartilage to evaluate the significance of PG depletion-induced changes In MR relaxation parameters. These comparisons were conducted for both uncompressed and mec hanically compressed states. The mechanical compressions were performed wit h an MR-compatible pressure cell and evaluated dynamically via interleaved one-dimensional proton and sodium MR projection imaging. The comparisons in dicate that sodium relaxation parameters are sensitive to PG depletion when cartilage is in a mechanically compressed state or an uncompressed state. In contrast, proton relaxation parameters do not change significantly with PG depletion when cartilage is in an uncompressed state. However, during me chanical compression, proton T2 becomes sensitive to PG depletion. These re sults support the potential of sodium magnetic resonance imaging (MRI) as a possible modality for obtaining imaging contrast related to PG depletion. The results also indicate the potential of proton MRI to provide such contr ast if the image acquisition is conducted in conjunction with a mechanical compression via physical exercise. (C) 1999 Wiley-Liss, Inc.