HIGH-RESOLUTION MAGNETIC-RESONANCE-IMAGING OF ARTHRITIC PATHOLOGY IN THE RAT KNEE

High-resolution magnetic resonance imaging (MRI) has been used to visu alise the changes that occur in both soft tissue and bone during antig en-induced, monoarticular arthritis (AIMA) of the rat knee. Extensive optimisation studies were performed in order to minimise the time of t he experiments and to maximise both the signal-to-noise ratio and the contrast in the MR images. The study was cross-sectional rather than l ongitudinal and at each of the 13 time points studied during the progr ession of the disease, corresponding X-radiographs and histological se ctions were obtained. Interpretation of the spin echo MR images was ai ded by the use of chemical shift-selective imaging, magnetisation tran sfer contrast and relaxation time experiments, as well as by correlati on with the histology and X-radiography data. The MR images clearly sh ow invasion of the synovium by an inflammatory pannus which spreads ov er the articular cartilage and invades the bone, leading to erosion an d later remodelling. Two distinct types of bony erosion were observed: focal erosions, especially at the margins of the joint, and subchondr al erosions. It is concluded that MRI provides a sensitive, non-invasi ve method for investigating both early-stage inflammatory changes and late-stage bony changes in the knee joints of the arthritic rat.