x-ray

An X-ray is a quick, painless test that produces images of the structures inside your body — particularly your bones.

X-ray beams pass through your body, and they are absorbed in different amounts depending on the density of the material they pass through. Dense materials, such as bone and metal, show up as white on X-rays. The air in your lungs shows up as black. Fat and muscle appear as shades of gray.

For some types of X-ray tests, a contrast medium — such as iodine or barium — is introduced into your body to provide greater detail on the images.

What are medical x-rays?

X-rays are a form of electromagnetic radiation, like visible light. Unlike light, however, x-rays have higher energy and can pass through most objects, including the body. Medical x-rays are used to generate images of tissues and structures inside the body. If x-rays traveling through the body also pass through an x-ray detector on the other side of the patient, an image will be formed that represents the “shadows” formed by the objects inside of the body.

One type of x-ray detector is photographic film, but there are many other types of detectors that are used to produce digital images. The x-ray images that result from this process are called radiographs.

The electromagnetic spectrum. X-rays have higher energy than visible light. Credit: iStock

How do medical x-rays work?

To create a radiograph, a patient is positioned so that the part of the body being imaged is located between an x-ray source and an x-ray detector. When the machine is turned on, x-rays travel through the body and are absorbed in different amounts by different tissues, depending on the radiological density of the tissues they pass through. Radiological density is determined by both the density and the atomic number (the number of protons in an atom’s nucleus) of the material being imaged. For example, our bones contain calcium, which has a higher atomic number than most other tissues. Because of this property, bones readily absorb x-rays and therefore produce high contrast on the x-ray detector. As a result, bony structures appear whiter than other tissues against the black background of a radiograph. Conversely, x-rays travel more easily through less radiologically dense tissues, such as fat, muscle, and air-filled cavities such as the lungs. These structures are displayed in shades of gray on a radiograph.

Why it's done

X-ray technology is used to examine many parts of the body.

Bones and teeth

• Fractures and infections. In most cases, fractures and infections in bones and teeth show up clearly on X-rays.
• Arthritis. X-rays of your joints can reveal evidence of arthritis. X-rays taken over the years can help your doctor determine if your arthritis is worsening.
• Dental decay. Dentists use X-rays to check for cavities in your teeth.
• Osteoporosis. Special types of X-ray tests can measure your bone density.
• Bone cancer. X-rays can reveal bone tumors.

Chest

• Lung infections or conditions. Evidence of pneumonia, tuberculosis or lung cancer can show up on chest X-rays.
• Breast cancer. Mammography is a special type of X-ray test used to examine breast tissue.
• Enlarged heart. This sign of congestive heart failure shows up clearly on X-rays.
• Blocked blood vessels. Injecting a contrast material that contains iodine can help highlight sections of your circulatory system to make them visible on X-rays.

Abdomen

• Digestive tract problems. Barium, a contrast medium delivered in a drink or an enema, can help reveal problems in your digestive system.
• Swallowed items. If your child has swallowed something such as a key or a coin, an X-ray can show the location of that object.

How you prepare

Different types of X-rays require different preparations. Ask your doctor or nurse to provide you with specific instructions.

What to wear

In general, you undress whatever part of your body needs examination. You may wear a gown during the exam, depending on which area is being X-rayed. You may also be asked to remove jewelry, eyeglasses and any metal objects because they can show up on an X-ray.

Contrast material

Before some types of X-rays, you're given a liquid called contrast medium. Contrast mediums, such as barium and iodine, help outline a specific area of your body on the X-ray image. You may swallow the contrast medium or receive it as an injection or an enema.

What you can expect

During the X-ray

X-rays are performed at doctors' offices, dentists' offices, emergency rooms and hospitals — wherever an X-ray machine is available. The machine produces a safe level of radiation that passes through your body and records an image on a specialized plate. You can't feel an X-ray.

A technologist positions your body to obtain the necessary views. He or she may use pillows or sandbags to help you hold the position. During the X-ray exposure, you remain still and sometimes hold your breath to avoid moving so that the image doesn't blur.

An X-ray procedure may take just a few minutes for a simple X-ray or longer for more-involved procedures, such as those using a contrast medium.

Your child's X-ray

If a young child is having an X-ray, restraints or other techniques may be used to keep him or her still. These won't harm your child and will prevent the need for a repeat procedure, which may be necessary if the child moves during the X-ray exposure.

You may be allowed to remain with your child during the test. If you remain in the room during the X-ray exposure, you'll likely be asked to wear a lead apron to shield you from unnecessary exposure.

After the X-ray

After an X-ray, you generally can resume normal activities. Routine X-rays usually have no side effects. However, if you're injected with contrast medium before your X-rays, drink plenty of fluids to help rid your body of it. Call your doctor if you have pain, swelling or redness at the injection site. Ask your doctor about other signs and symptoms to watch for.

How are X-rays performed?

X-rays can be performed on an outpatient basis, or as part of inpatient care.

Although each facility may have specific protocols in place, generally, an X-ray procedure follows this process:

• The patient will be asked to remove any clothing or jewelry which might interfere with the exposure of the body area to be examined. The patient will be given a gown to wear if clothing must be removed.
• The patient is positioned on an X-ray table that carefully positions the part of the body that is to be X-rayed--between the X-ray machine and a cassette containing the X-ray film or specialized image plate. Some examinations may be performed with the patient in a sitting or standing position.
• Body parts not being imaged may be covered with a lead apron (shield) to avoid exposure to the X-rays.
• The X-ray beam will be aimed at the area to be imaged.
• The patient must be very still or the image will be blurred.
• The technologist will step behind a protective window and the image is taken.
• Depending on the body part under study, various X-rays may be taken at different angles, such as the front and side view during a chest X-ray.