X-ray is the most important method for determining the scope and severity of osteoarthritis. Any chronic joint pain should be evaluated with X-rays, which can help rule out nonarthritic conditions such as tumors or infection. Magnetic resonance imaging (MRI) is best used in the evaluation of soft tissues, such as ligaments. Torn ligaments are frequent causes of joint pain. MRI also can show the thickness of articular cartilage-the elastic tissue that covers the ends of joint bones-thus obtaining a clearer picture of the severity of the arthritis. Computed tomography (CT) scans or ultrasound are useful for special circumstances, such as viewing internal organs and assessing blood flow, but are not routine for the evaulation of arthritis.