Magnetic resonance (MR) imaging has proven to be an accurate noninvasive method for the evaluation of articular cartilage [1–13], demonstrating morphologic changes as well as biochemical and structural changes. This chapter will concentrate on the morphologic imaging of articular cartilage and articular cartilage repair procedures using MR. Multiple MR pulse sequences have been used to evaluate the morphology of articular cartilage, but the most widely used clinically are proton density or T2- weighted fast spin-echo (FSE, TSE) sequences with or without fat suppression.

Fast spin-echo sequences employ multiple refocusing pulses that allow high-resolution images to be acquired in a relatively short time period. In addition, the multiple refocusing pulses produce a magnetization transfer effect within articular cartilage, which decreases its signal intensity. There is no corresponding effect within joint fluid, and therefore the magnetization transfer effect increases the contrast between articular cartilage and joint fluid, and improves the conspicuity of chondral defects. Studies have shown both proton density and T2-weighted fast spin-echo images with and without fat suppression to be accurate in the detection of chondral abnormalities. On fast spin echo images, cartilage has intermediate signal intensity tissue and is outlined by high signal intensity joint fluid providing excellent depiction of surface morphology as well as intrinsic signal changes potentially reflective of intrasubstance pathology. Chondral lesions appear as focal areas of increased signal intensity compared with normal surrounding cartilage. Although images without fat suppression have been shown to be accurate, the addition of fat suppression improves the ability to detect underlying subchondral bone marrow signal changes, which have been shown to be an important indicator of overlying articular cartilage defects. Studies have demonstrated a sensitivity of 86–94%, specificity of 94–99%, and accuracy of 81–98% for the detection of cartilage abnormalities on fast spin-echo techniques.

Over the past several years, three-dimensional (3D) fast spin-echo sequences have been developed, and these offer the promise of isotropic resolution and multiplanar reconstructions without loss of resolution while maintaining the excellent contrast of two-dimensional (2D) fast spin-echo sequences with reasonable times of acquisition (6–8 min) [14–16]. Initial studies have demonstrated equivalent diagnostic performance with 2D fast spin-echo sequences. 3T MR imaging and multichannel coils have also been utilized in cartilage imaging to take advantage of the potential advantages of imaging with relative increased image signal-to-noise or higher spatial resolution at similar imaging acquisition times, compared with 1T or 1.5T imaging (albeit with somewhat increased sensitivity to postoperative metal-related artifacts) [17, 18].