[MRI and articular cartilage]

Although plain films are fundamental for routine imaging of degenerative chondral lesions, MRI is a promising tool of investigation for the articular cartilage. Its modalities are still imprecise and debated, but, because of its noninvasiveness, it is destined to be preferred over arthroCT. The small size of the cartilage requires thin slices of less than 3-mm thick. The various features of normal cartilage images must be well known. They depend on acquisition parameters, zonal structure of the cartilage and numerous artifacts (partial volume average, chemical shift, magnetic susceptibility, truncation, "magic angle"). Fast SE images provide a good compromise between contrast and the signal-to-noise ratio. T2-weighted images take advantage of an arthrographic effect in case of joint effusion. 3D GE images allow a more accurate evaluation with 1-mm thick slices. In all sequences, adding of a fat-suppression presaturation increases contrast between the cartilage and the surrounding structures. The diagnostic accuracies of the different sequences and of MR arthrography are discussed. Quantitative measurements of cartilage thickness and volume remain the topic of clinical research.