USE OF NITROXIDES AS NMR CONTRAST ENHANCING AGENTS FOR JOINTS

NMR imaging is a well-established technology for obtaining cross-secti onal anatomic pictures of organs and tissues. In addition, NMR can pro vide valuable information about the physiologic state of organs and ti ssues, especially, as a consequence of cellular injury. With this in m ind, NMR in combination with gadolinium-based contrast enhancing agent s has been used to assist in the detection of abnormalities to joints as well as to evaluate the status of damage resulting from an injury t o this site. We describe the synthesis of a new nitroxide, which is bi oresistant to the one-electron reduction mediated by superoxide in the presence of cysteine. This model mimics the reduction of nitroxides b y extracellular secretion of superoxide by PMA-stimulated neutrophils. With this nitroxide, we found, in the range from 15 to 17.5 mu moles, enhancement of an NMR image in the knee joint of rabbits. Of interest is the finding that the contrast image remained for at least 90 minut es. These results demonstrate the utility of nitroxides as contrast en hancing agents for NMR imaging of joints.