In a healthcare 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) block most of the photons and appear white on developed film. Structures containing air are black on film, and muscle, fat, and fluid appear as shades of gray. Metal and contrast medica (intravenous or oral contrast) block almost all the photons and 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 healthcare 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 or not move during the brief (approximately 1 second) exposure.

How to prepare for the test
Inform the healthcare provider prior to the exam if you are pregnant, may be pregnant or have a Intra-Uterine Device (IUD) inserted.

Remove all jewelry and a hospital gown is worn during the x-ray examination, because metal and certain clothing can obscure the images and require repeat studies.

How will the test 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.

Risks
During a single radiograph, a small function of the x-rays pass 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 (due to damaged ovarian cells or sperm cells) is low. Most experts feel that the 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 healthcare providers about suspected pregnancy.