Radiography involves exposing a part of the body to a small dose of radiation to produce an image of the internal organs. Organs with high density such as the ribs and spine are radiopaque, meaning they do not absorb radiation, and appear white or light grey on the image. Lung tissue is radiolucent-absorbs radiation- and appears dark on the image.

Before some types of X-rays, patients are given a liquid called a contrast medium, such as barium or iodine, which is radiopaque and allows the organ or tissue it fills to be examined. The contrast medium may be swallowed, introduced through the anus as an enema, or given as an injection.

Radiology is the use of radiation in the diagnosis and treatment of diseases such as cancer.

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