General Radiography

Alternative names
X-ray; Plain films


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 basic science of X-ray generation and detection is the key behind general radiographs of the body, mammography, fluoroscopy (real-time imaging on video screens), and computed tomography (CT).

How the test is performed

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.

How to prepare for the test

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.

How the test will feel
There is no discomfort from X-ray exposure. Patients may be asked to stay still in awkward positions for a short period of time.

What the risks are

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

Johns Hopkins patient information

Last revised: December 7, 2012
by Mamikon Bozoyan, M.D.

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