Magnetic resonance studies of cartilage osmotic and mechanical properties

Articular cartilage, the tissue that coats the ends of bones in synovial joints, is remarkable in that it is solid while being primarily composed of water. The progressive deterioration of articular cartilage debilitates over 20% of the human population. Most major pharmaceutical companies actively pursue cartilage regenerative therapies; however, it is difficult to test the effectiveness of novel treatments since cartilage condition cannot be monitored non-invasively. Here, we present several new ways to assess cartilage softening via magnetic resonance imaging (MRI). Cartilage softening is one of the earliest manifestations of cartilage degeneration. First, a new quantitative osmotic model of cartilage rheology is developed. Then, the equilibrium of a charged MR contrast agent is used to confirm the osmotic properties that are hypothesized to give cartilage its strong compressive resistance. A novel method for mechanically compressing cartilage specimens in an imaging environment is then demonstrated. Conventional MRI parameters of articular cartilage are presented as a function of compression. One major advantage that this new technique has over purely mechanical studies is that, during compression, positional cartilage water content can be dynamically mapped. Additional techniques are presented: one for dynamically measuring cartilage fluid permeability, and a second for spatially mapping cartilage rheological properties. The osmotic model is then further confirmed by interleaved sodium and proton imaging during compression