Since Röntgen's discovery that X-rays can identify bony structures, X-rays have been developed for their use in medical imaging.
X-rays are useful in the detection of pathology of the skeletal system as well as for detecting some disease processes in soft tissue. Some notable examples are the very common chest X-ray, which can be used to identify lung diseases such as pneumonia, lung cancer or pulmonary edema, and the abdominal X-ray, which can detect intestinal obstruction, free air (from visceral perforations) and free fluid (in ascites). X-rays may also be used to detect pathology such as gallstones (which are rarely radiopaque) or kidney stones which are often (but not always) visible. Traditional plain X-rays are less useful in the imaging of soft tissues such as the brain or muscle. X-rays are also commonly used in dentistry, as X-ray imaging is useful in the diagnoses of common oral problems, such as cavities.