Measures of molecular composition and structure in osteoarthritis.

Osteoarthritis involves ongoing degradative and healing processes that occur at the molecular level in multiple tissues in the joint in response to a number of biochemical and mechanical factors. Understanding these dynamic processes before they affect the structural aspects of the joint motivates the need for metrics to better visualize the compositional and structural molecular aspects of the tissues in vivo. As reviewed here, most of the work to date in this regard has been focused on magnetic resonance imaging approaches for interrogating molecular features of cartilage, including T2 mapping, T1rho mapping, delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC), and sodium imaging. Specific examples illustrate new opportunities and insights emerging from these methods.