What are the advantages and disadvantages of the common imaging modalities used to evaluate arthritis?
Conventional radiography is the mainstay for the initial workup of patients with various arthritides. It is a relatively inexpensive imaging technique that allows the radiologist to detect the presence of and characterize the type of arthritis based upon the pattern of observed changes that involve the bones, joints, and soft tissues. However, the pathologic changes that occur early in the disease process may be occult on radiographs, particularly when involving the soft tissue structures. For this reason, magnetic resonance imaging (MRI) is useful to evaluate early changes such as joint effusions, synovitis, cartilage abnormalities, bone marrow edema, osseous erosions, and tendon and ligament abnormalities. Ultrasonography (US) is an imaging technique that may be used to evaluate patients with arthritis. While it is less expensive than MRI, it is operator dependent. Bony erosions that may be occult on radiographs can be visible on gray scale US. US is also useful to evaluate for presence of associated tendon and ligament abnormalities, intraarticular bodies, joint effusions, and extraarticular fluid collections. Color Doppler US is useful to demonstrate synovial hyperemia, which is common in the inflammatory arthropathies. 18 F-fluorodeoxyglucose (FDG) positron emission tomography (PET) is also useful to reveal increased metabolic activity in sites of active arthritis, but it is only currently utilized for research purposes.