Chest X-Ray
Medical Author: Siamak Nabili, MD, MPH
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR
What is a chest X-ray?
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 (which is filled with
mostly air) absorbs very little, allowing most of the X-ray beam to pass through
the lung.
What is a shadow on a chest X-ray?
Due to the differences in their composition (and, therefore, varying degrees
of penetration of the X-ray beam), the lungs, heart, aorta, and bones of the
chest each can be distinctly visualized on the chest X-ray. The X-ray film
records these differences to produce an image of body tissue structures and
these are shadows seen on the X-ray. The white shadows on chest X-ray represent
more dense or solid tissues, such as bone or heart, and the darker shadows on
the chest X-ray represent air filled tissues, such as lungs.
Next: How is the chest X-ray procedure performed? »
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