This page was reviewed under our medical and editorial policy by

Maurie Markman, MD, President, Medicine & Science

This page was updated on May 2, 2022.

An X-ray is a common imaging test that takes pictures of the inside of the body. X-rays use a small amount of radiation that passes through the body and creates a digital image of bones, organs and tissues. They help doctors diagnose, monitor and plan treatments for many conditions, including some cancers. 

What is the reason for getting an X-ray?

You might have an X-ray for a number of reasons: They are used to help doctors look for cancer in the bones, lungs, stomach, kidneys or breasts, for example. A mammogram is a type of X-ray. 

They are also used to see how some treatments are working and to help plan for surgery, and they can help doctors place catheters and stents that are used to treat some cancers.

Contrast studies are special kinds of X-ray tests that use iodine or barium to get organs to show up better and in more detail. You will need to take the “contrast medium” before the test, and you may be asked to swallow a liquid, get an injection or have an enema, depending on the kind of test. For example:

  • A lower GI series or barium enema uses an enema to fill the lower intestine before an X-ray of the colon and rectum.
  • An upper GI series or barium swallow is a test that requires you swallow a barium mixture and then undergo a series of X-rays as the mixture coats your esophagus and stomach.
  • An intravenous pyelogram (IVP) uses an injection of a special dye before an X-ray of the kidneys and bladder.

How do X-rays work?

An X-ray machine sends out a beam of electromagnetic radiation that passes through the body. As it travels, different parts of the body absorb different amounts of the energy.

Dense areas, like bone, block more of the radiation, giving them a white appearance on an X-ray. Fat and muscle absorb less, so they show up in different shades of gray. The lungs look black because they are filled with air. Tumors often show up as lighter gray than the surrounding tissue. After it passes through the body, the X-ray hits a special detector that creates the image on a computer (digital image). A radiologist, a doctor trained in evaluating imaging scans, will examine the X-ray and interpret the findings.

What to expect during an X-ray

For a standard X-ray, you usually don’t have to do anything special to prepare. Be sure to tell the technologist if you are pregnant or might be pregnant.

You’ll take off clothes that are on the part of your body that will be X-rayed. You may need to remove jewelry, eyeglasses and metal items as well, so they don’t show up in the X-ray. Depending on what part of your body will be X-rayed, you may wear a hospital gown.

An X-ray technologist will help position your body next to a plate that creates the image. You may be asked to stand, sit or lie down. The technologist may put a special shield on other parts of your body that are close to the area being X-rayed, so they are not exposed to radiation.

The technologist may move the X-ray camera to focus on the specific area of your body. He or she may leave the room to turn the machine on, avoiding exposure to radiation. It’s important to hold still while the X-ray is being taken. You may hear a click or a buzzing sound. It usually takes less than a second to take the X-ray, and the procedure is painless.

Sometimes, the technologist will ask you to reposition your body and take another image from a different angle. For example, if you are having a chest X-ray, you may have one image taken from the front and one from the side.

If you are having an X-ray with contrast medium, your doctor may give you special instructions to follow before and after the procedure.  

What are the risks of an X-ray?

An X-ray exposes parts of the body to a low dose of radiation. Because the amount is low, research suggests that the benefits outweigh the risks.

Some people may have side effects from the injection of a contrast medium, such as feeling warm, lightheaded or nauseous, itching or a metallic taste in the mouth. Rarely, some people may have a more serious allergic reaction.

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