X-rays are the most frequently used form of medical imaging. Conventional X-rays are performed for a variety of reasons, but are most commonly done to detect problems in the bones and chest.
An X-ray image is produced when a small amount of radiation is passed through a body part to expose a sensitive surface (historically a film) that is positioned on the other side. The image is produced as a result of the ways in which different internal structures absorb the radiation. For example, bones tend to stop the X-rays and cause a definite shadow. The lungs, which are filled with air, allow nearly all the X-rays to pass through, causing very little shadow.