Magnetic resonance imaging (MRI) uses radiofrequency waves and a strong magnetic field rather than X-rays to provide remarkably clear and detailed pictures of internal organs and tissues. The technique has proven valuable for the diagnosis of a broad range of pathologic conditions in all parts of the body, including stroke, cancer, heart and vascular disease, joint and musculoskeletal disorders. MRI requires specialized equipment and expertise and allows evaluation of some body structures that may not be as visible with other imaging methods.