X-rays are a form of electromagnetic radiation, just like visible light. In the health care setting, an X-ray machine sends individual X-ray particles through the body. For most conventional x-rays, the risk is very low. A computer is used to record the images that are created. Structures that are dense (such as bone) will block most of the x-ray particles, and will appear white. Metal and contrast media (special dye used to highlight areas of the body) will also appear white. Structures containing air will be black, and muscle, fat, and fluid will appear as shades of gray. 
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How the Test is Performed
The test is performed in a radiology department 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 or not move during the brief exposure (about 1 second).
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 4 days, the test may be delayed until the contrast has fully passed.

You will remove all jewelry and wear a hospital gown during the X-ray examination because 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.
Most experts feel X-rays are low risk and are 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 fetuses are more sensitive to the risks of X-rays. Women should tell health care providers if they think they are pregnant.