X-rays are a form of radiation, like light or radio waves, that can be focused in a beam, much like a flashlight beam. Unlike a beam of light, however, X-rays can pass through most objects, including the human body. When X-rays strike a piece of photographic film, they can produce a picture. Dense tissues in the body, such as bones, block many of the X-rays and appear white on an X-ray picture. Less dense tissues, such as muscles and organs, block fewer of the X-rays and appear in shades of gray. X-rays that pass only through air appear black.

Before the X-ray test, tell your doctor if you are or might be pregnant. Pregnancy and risk of radiation exposure to the fetus must be considered. The risk of damage from the X-rays is usually very low compared with the potential benefits of the test. Also, tell your doctor if you have undergone an X-ray test using a barium contrast material (such as a barium enema) within the past 4 days. Barium shows up on X-ray films and can interfere with the results of an X-ray.

An X-ray is taken by a radiology technologist. The X-ray pictures are usually interpreted by a doctor who specializes in evaluating X-rays (radiologist). You will need to remove any jewelry that might interfere with the X-ray picture. You may need to take off some or all of your clothes, depending on which area is examined. You will be given a cloth or paper covering to use during the test. During the X-ray test, you will lie on an X-ray table. You will be placed in different positions to obtain the needed views. If the X-ray is being taken because of a possibly serious injury to part of your body, a radiologist will review the first pictures to prevent further injury before taking others. Usually 3 to 5
X-ray pictures are taken. You need to lie very still to avoid blurring the pictures. You will feel no discomfort from the X-rays. However, the X-ray table may feel hard and the room may be chilly because air-conditioning is used to keep the X-ray equipment at a constant temperature. You may find that the positions you need to hold are uncomfortable or painful, especially if you have an injury.

There is always a slight risk of damage to cells or tissue from being exposed to any radiation, including the low levels of X-rays used for this test. However, if this test is really needed, the risk of damage from the X-rays is usually very low compared with the potential benefits of the test. There are precautions you can take to reduce your risk of radiation exposure from X-rays. In an emergency, the results of an X-ray can be available within a few minutes. Otherwise, the results are usually ready within a day.