Update on imaging in rheumatic diseases: cartilage.

In recent years, the role of articular cartilage for understanding pathogenesis as well as for clinical research has become increasingly important. Whereas previously cartilage could only be assessed invasively, various imaging procedures are available for its evaluation now. Although still widely used, conventional radiography bears significant limitations since it assesses cartilage indirectly by joint space width. Today, the cartilage thickness and structure can be reliably evaluated using ultrasound, although the molecular structure cannot be determined, yet. Besides ultrasound, MRI offers the possibility to image morphological changes with a very high resolution. In addition, the quality and composition of joint cartilage can already be measured due to a constant technical improvement and new MRI sequences such as dGEMRIC even in small joints (e.g. MCP or MTP joints). Despite the advantages of contrast agents for the detection of inflammation, its use is reevaluated today. Regarding that contrast agent-free imaging techniques for the assessment of joint cartilage are developed with great effort to depict its quality and changes over time. These novel MRI methods such as T2/T2*- and T1ρ-mapping, gagCEST, and sodium imaging provide promising quantitative imaging biomarkers that can detect early cartilage changes before morphological alterations occur. Hence, US and MRI will likely be of paramount importance in future clinical trials and clinical assessment of inflammatory and degenerative joint diseases not only for understanding pathogenesis but also for using its possible value in daily practice.