X-rays are a form of electromagnetic radiation, just like visible light. In a health care setting, X-rays are emitted by a machine as individual "particles" (photons) that pass through the body and then get detected by a sensitive film.

Structures that are dense (such as bone) will block most of the photons, and will appear white on developed film. Structures containing air will be black on film, and muscle, fat, and fluid will appear as shades of gray. Metal and contrast media (intravenous or oral contrast) blocks almost all the photons and will appear bright white.

The test is performed in a hospital radiology department or in the health care provider's office by an X-ray technologist. The positioning of the patient, X-ray machine, and film depends on the type of study and area of interest. Multiple individual views may be requested.

Much like conventional photography, motion causes blurry images on radiographs, and thus, patients may be asked to hold their breath and/or not move during the brief (approximately one second) exposure.

Inform the health care provider prior to the exam if you are pregnant, may be pregnant, or have an IUD inserted.

If abdominal studies are planned and you have had a barium contrast study (such as a barium enema, upper GI series, or barium swallow) or taken medications containing bismuth (such as Pepto Bismol) in the last four days, the test may be delayed until the contrast has fully passed.

You should remove all jewelry and wear a hospital gown during the X-ray examination since metal and certain clothing can obscure the images and require repeat studies.

During a single radiograph, a small fraction of the X-rays pass right through the body. The remaining photons are absorbed by tissues in the body. The energy of the absorbed photons can break apart (ionize) compounds, and this may cause cell damage. Most cell damage is soon repaired. However, some is permanent.

For the exposures encountered in conventional radiography, the risk of cancer or heritable defects (via damaged ovarian cells or sperm cells) is very low. Most experts feel that this low risk is largely outweighed by the benefits of information gained from appropriate imaging. X-rays are monitored and regulated to provide the minimum amount of radiation exposure needed to produce the image.

Young children and a developing fetus carried by pregnant women are more sensitive to the risks of X-rays. Women should tell health care providers about suspected pregnancy.

For additional information regarding why the test is performed and normal and abnormal results, please see the specific X-ray topics:

• dental X-rays
• neck X-ray
• sinuses X-ray
• pelvis X-ray
• thoracic spine X-ray
• hands X-ray
• lumbosacral spine X-ray
• skull X-ray
• extremity X-ray
• bone X-ray
• joints X-ray
• chest X-ray
• abdominal X-ray
• barium X-ray
• gallbladder X-ray
• X-ray of the skeleton