An X-ray examination uses electromagnetic radiation to make images of your bones, teeth and internal organs. Simply put, an X-ray allows your doctor to take pictures of the inside of your body.

One of the oldest forms of medical imaging, X-ray is a painless medical test that can help your doctor in diagnosis and treatment — even in emergency situations. It's a fast, easy and safe way for your doctor to view and assess conditions ranging from broken bones to pneumonia to cancer. Many different types of X-rays, such as bone or chest X-rays, exist. The type your doctor uses depends on what part of your body is being examined and for what purpose.

• Determine whether a bone is chipped, dislocated or broken (fractured)
• Evaluate joint injuries and bone infections
• Diagnose and monitor the progression of degenerative conditions, such as arthritis and the bone-thinning disease osteoporosis
• Screen for lung and heart diseases
• Find and treat artery blockages
• Diagnose the cause of persistent coughing or chest pain
• Check for broken ribs or a punctured lung
• Evaluate abdominal pain
• Locate objects that may have been accidentally swallowed by a child
• Determine whether you have injured a bone or disk in your spine
• Detect scoliosis, an abnormal curvature of the spine, and other spinal defects
• Evaluate infection of the sinuses (sinusitis)
• Locate dental problems such as cavities, abscessed teeth and other tooth and jaw abnormalities

X-ray exams also play an important role in the detection and diagnosis of cancer. In fact, one use of X-ray in diagnosing cancer is to see whether you have lung cancer or whether cancer from another part of the body has spread (metastasized) to the lungs. Cancer may appear lighter in color on X-ray films than does normal, healthy lung tissue. X-rays may also be used to examine cancers of the intestines, stomach, liver, spleen, kidneys and breasts.

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

In general, you undress the area of your body that needs examination. You may wear a gown to cover yourself during the exam, depending on what area is being X-rayed. You may also be asked to remove jewelry, eyeglasses and any metal objects or clothing that may obscure the X-ray image, since these objects can show up on an X-ray.

You may be asked to wear a lead apron to shield your sex organs from exposure to the X-rays. At very high doses, radiation can damage a woman's eggs or a man's sperm. Since you're exposed to a small amount of radiation during most X-rays, the lead apron is used simply as a precaution.

At high doses, radiation can be harmful to a fetus. Always inform the X-ray technologist if there's any possibility that you might be pregnant. Your doctor may suggest that you either forego the X-ray exam or, if one is necessary at the time, take precautions to minimize radiation exposure to the fetus.

Before some types of X-rays you're given a liquid called contrast medium, or a dye. Contrast mediums, such as barium and iodine, help outline a specific area of your body on X-ray film. You may swallow the contrast medium, insert it as an enema or receive it as an injection. The contrast medium appears opaque on X-ray film, providing clear images of structures such as your digestive tract or blood vessels.

If you're to receive a contrast medium before an X-ray, tell your doctor if you have a history of allergy to X-ray dye, such as iodine.

An X-ray machine produces an X-ray beam using a tube that is carefully aimed and focused on the body part being examined. The machine produces a tiny burst of radiation, at a safe level, that passes through your body and records an image on film or on a specialized plate.

As X-rays pass through your body, different tissues absorb different amounts of the X-rays. For example, your bones are dense and absorb X-rays well. But soft tissues, such as your skin, fat, muscles and organs, allow more X-rays to pass through them. The result is that bones appear white on the X-ray. Your other tissues appear in varying shades of gray. Structures containing air, such as your lungs, appear dark.

X-rays are performed at most doctors' offices, dentists' offices, emergency rooms and hospitals — wherever an X-ray machine is available. If you need an X-ray, you're brought to a room with an X-ray machine and table- or wall-mounted equipment containing X-ray film or a specialized plate for digital recording.

As you lie on a table, sit or stand between the X-ray machine and the X-ray film or plate, the technologist or a radiologist — a doctor who specializes in interpreting X-rays and other imaging tests — positions your body to obtain the necessary views. He or she may use pillows or sandbags to help you hold the proper position. The technologist then aims the machine at the area of your body that needs examination. For dental X-rays, the dentist or dental hygienist places a small piece of film in your mouth, behind the teeth being X-rayed. You're asked to bite down on the paper tab around the film, to hold the film in place.

Once you're in the proper position, the technologist enters a shielded control booth. During the X-ray exposure, you remain still and hold your breath to avoid moving, which can cause blurring on the film.

The technologist may take X-rays from multiple angles — for example one of the front and one from the side of your chest.

If a young child is having an X-ray, restraints may be used to help keep him or her still. You may be allowed to remain with your child during the test. If you remain in the room during the X-ray exposure, you're typically given a lead apron to wear to shield you from unnecessary exposure.

An X-ray procedure may take only a few minutes for a bone X-ray, or more than an hour for more involved procedures, such as those using a contrast medium.

For most X-rays, you feel no discomfort other than the hardness of the X-ray table or the temperature of the room, which may be kept cool to keep the equipment from overheating. It may be necessary to compress momentarily the body part being examined. This compression may be uncomfortable, but the discomfort lasts only briefly during the X-ray exposure. If you're having a test that requires contrast medium, ask your doctor what to expect.

After an X-ray, you generally can resume normal activities. Routine X-rays usually have no side effects. However, if you receive an injection of contrast medium before your X-rays, call your doctor if you experience pain, swelling or redness at the injection site. Ask your doctor about other signs and symptoms to watch for pertaining to your specific X-ray procedure.

X-rays are recorded on film or are recorded digitally. They can be viewed on-screen within minutes. A radiologist typically views and interprets the results and sends a report to your doctor, who then explains the results to you. In an emergency, your X-ray results can be made available to your doctor in minutes.

You may worry that X-rays aren't safe because it's known that high levels of radiation exposure can cause cell mutations that may lead to cancer. But the amount of radiation you're exposed to during an X-ray is so small that the risk of any damage to cells in your body is extremely low.

So for most X-ray examinations, the benefits of a medically indicated examination are thought to greatly outweigh the small risk. In addition, great care is taken to use the lowest radiation dose possible to produce the best images for the radiologist to evaluate. No radiation remains after an X-ray examination.

However, if you're pregnant or suspect that you may be pregnant, inform your doctor before having an X-ray. Though the risk of most diagnostic X-rays to an unborn baby is small, your doctor may consider whether it's better to wait or to use another imaging test such as ultrasound.