Molecular (and functional) imaging of articular cartilage.

Abstract

Considerable progress has been made over the past decade in developing imaging methods for quantifying cartilage morphology. Over the coming decades, these methods will likely be supplemented by non-destructive or imaging by MRI to provide an adjunct or surrogate for the destructive histological and biochemical assays used today. In this talk, we will provide a brief overview of emerging strategies for assessing cartilage molecular state – i.e., its biochemical composition and architecture. Importantly, the macromolecular status of cartilage is inextricably linked to the functional integrity of the tissue. In particular, studies suggest that solid/fluid volume fraction, collagen composition, molecular structure and organization, and GAG composition are key macromolecular features that they have interdependent effects on functional integrity of cartilage. Accordingly, these macromolecular features have been the focus of efforts to develop non-destructive imaging methods. Techniques under development range from those specific to a given biochemical species (water, collagen ultrastructure, and GAG) to those that appear through correlative studies to have image contrast that is modulated by a particular combination of macromolecules. Our talk will briefly comment on many of the methods that have been used, and then look in some depth at several. Water content can be measured directly and specifically using proton density imaging. The practical challenge lies in the sensitivity, because the variation of water content across disease states is less than 5%. As noted below, there are some MR contrast mechanisms that can overemphasize this significant but small change in proton density – albeit at the