MR imaging is able to demonstrate both the structural changes that occur in rheumatoid arthritis and the inflammatory changes, including synovial proliferation and joint effusion. MR imaging can demonstrate erosion before it is visible on radiographs. Although MR imaging appears to be very helpful in assessing the severity of rheumatoid arthritis and its response to therapy, the optimal technique for this assessment and the ultimate clinical value of MR imaging have yet to be determined.