New MRI techniques for imaging cartilage.

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Because of its ability to image all of the tissues in a diarthrodial joint, magnetic resonance imaging (MRI) has an ever-increasing role in the evaluation, diagnosis, and monitoring of joint disorders. Standard MRI techniques can delineate morphologic abnormalities. Techniques on the horizon offer improved morphologic analysis as well as previously unavailable information about the biochemical composition and functional properties of joint tissues. While research and development efforts are rapidly growing, the current review focuses on techniques that are most advanced and that have demonstrated feasibility in basic science and clinical studies. As such, we report mainly on cartilage imaging but hasten to add that ongoing research efforts offer promise for the imaging of all joint structures. These techniques should improve our ability to understand the healthy joint and the disease process, to provide earlier diagnoses, and to evaluate the effects of therapeutic procedures. With these capabilities, we can more effectively establish strategies to maintain joint health and to identify indications for intervention at an early stage of degeneration. We begin with an overview of the basics of MRI to provide the reader with a sense of what is measured and how an MR measurement is made. MRI is possible because nuclei with an odd number of protons and/or an odd number of neutrons have net magnetic moments. The most abundant nucleus in biological systems is the hydrogen nucleus (which, in MR vernacular, is referred to as a proton because hydrogen contains a single proton), making water and fat both observable with MRI. In all of the methods that we will discuss here (and virtually all of the MR imaging done clinically), it is the hydrogen (proton) nucleus that is being measured; indeed, the term MRI has come to be synonymous with the term proton-MRI (while MR of another nucleus x …