MRI AND ARTICULAR-CARTILAGE

Although plain films are fundamental for routine imaging of degenerati ve chondral lesions, MRI is a promising tool of investigation for the articular cartilage. Its modalities are still imprecise and debated, b ut, because of its noninvasiveness, it is destined to be preferred ove r arthroCT. The small size of the cartilage requires thin slices of le ss than 3-mm thick. The various features of normal cartilage images mu st be well known. They depend on acquisition parameters, zonal structu re of the cartilage and numerous artifacts (partial volume average, ch emical shift, magnetic susceptibility, truncation, '' magic angle ''). Fast SE images provide a good compromise between contrast and the sig nal-to-noise ratio. T2-weighted images take advantage of an arthrograp hic effect in case of joint effusion. 3D GE images allow a more accura te evaluation with I-mm thick slices. In all sequences, adding of a fa t-suppression presaturation increases contrast between the cartilage a nd the surrounding structures. The diagnostic accuracies of the differ ent sequences and of MR arthrography are discussed. Quantitative measu rements of cartilage thickness and volume remain the topic of clinical research.