A chest X-ray is a radiology test that involves exposing the chest briefly to radiation to produce an image of the chest and the internal organs of the chest. An X-ray film is positioned against the body opposite the camera, which sends out a very small dose of a radiation beam. As the radiation penetrates the body, it is absorbed in varying amounts by different body tissues depending on the tissue’s composition of air, water, blood, bone, or muscle. Bones, for example, absorb much of the X-ray radiation while lung tissue absorbs very little, allowing most of the X-ray beam to pass through the lung.