General Radiology X-ray is the original field from which radiology developed, and is probably still the most commonly employed form of radiology. X-rays can be taken either as still images or moving pictures, and often take little time to complete. They are frequently used to complement other kinds of radiology, such as MRIs, Ultrasounds, and CT Scans. The films created by X-rays show different features of the body in various shades of gray. The gray is darkest in those areas that do not absorb X-rays well; the grays are lighter in dense areas (like bones) that absorb more of the X-rays. Some X-ray exams improve visibility by using contrast, a range of substances which may be introduced into the patient by swallowing, injection, or enema.