Radiology

X rays are a type of radiant energy that occurs when a tungsten (a hard metallic element) target is bombarded with an electron beam. X rays are similar to visible light in that they radiate in all directions from their source. They differ, however, in that x rays are of shorter wavelength than ultraviolet light. This difference is the basis of radiology since the shorter wavelength allows x rays to penetrate many substances that are opaque to light.

An x ray of bones, organs, tumors, and other areas of the body is obtained through a cassette that holds a fluorescent screen. When activated by x rays, this screen emits light rays which produce a photochemical effect of the x rays on film. When light or x rays hit photographic film, a photochemical process takes place that results in the negative film turning black while the places not exposed to light remain clear. Images are obtained when the paper print of a negative reverses the image values. In the normal photographic process, an entire hand would be imaged because normal light cannot pass through the hand, thus creating the image on film. The desired x-ray image is obtained because x rays pass through outer tissue and are absorbed by bones and other structures, allowing them to be captured on film.

Over the years, radiology has fine tuned this approach to develop different x-ray devices for imaging specific areas of the body. For example, mammography is the radiological imaging of a woman's breast to determine the presence of diseases like breast cancer. Another major advance in x-ray technology was the development of radiopaque substances. When injected into the body, these substances, which do not allow x rays to pass through them, provide images of structures that would otherwise not appear on the x ray. For example, angiography is the imaging of blood vessels after injecting them with a radiopaque material. Myelography is the imaging of the spinal cord with x rays after injecting a radiopaque substance into a membrane covering the spine.