Update on magnetic resonance imaging and ultrasound in rheumatoid arthritis.

Rheumatoid arthritis (RA) disease activity often remains difficult to assess and quantify accurately. As a result, numerous measures using various techniques to estimate clinical activity have been developed for clinical research and care. More objective imaging biomarkers for early detection and accurate, quantitative measurement of the disease burden are therefore of interest both for clinical use and for investigational studies. Two widely studied imaging biomarkers are magnetic resonance imaging (MRI) and ultrasound (US), imaging tests that are increasingly available to clinicians. While substantial and increasing evidence has been reported that these tools are valid and provide advantages in both clinical trials and clinical assessments, more information is needed to inform their appropriate use in routine clinical care. The goals of this review are to outline the current literature regarding each of these objective imaging tools, assess their strengths and limitations, and to clarify knowledge gaps to be filled before these techniques may be more optimally utilised.