A form of electromagnetic radiation of short wavelength and high energy. X-rays are widely used in medicine for diagnosis and treatment because they can be used to image bones, organs, and internal tissues. X-rays are produced artificially by bombarding a heavy metal tungsten target with electrons, in a device known as an X-ray tube. Low doses of the X-rays that are emitted are passed through body tissue and form images on film or a fluorescent screen. The X-ray image, also known as a radiograph or roentgenogram, shows the internal structure of the area that is being examined. Dense structures, such as bone, absorb X-rays well and appear white on an Xray image. Soft tissues, such as muscle, absorb less and appear grey. Because X-rays can damage living cells, especially those that are dividing rapidly, high doses of radiation are used for treating cancer (see radiotherapy). Hollow or fluid-filled parts of the body often do not show up well on X-ray film unless they first have a contrast medium (a substance that is opaque to X-rays) introduced into them. Contrastmedium X-ray techniques are used to image the gallbladder (see cholecystography), bile ducts (see cholangiography), the urinary tract (see urography), the gastrointestinal tract (see barium X-ray examinations), blood vessels (see angiography; venography), and the spinal cord (see myelography). X-rays can be used to obtain an image of a “slice” through an organ or part of the body by using a technique known as tomography. More detailed images of a body slice are produced by combining tomography with the capabilities of a computer (see CT scanning). Large doses of X-rays can be extremely hazardous, and even small doses carry some risk (see radiation hazards). Modern X-ray film, equipment, and techniques produce high-quality images with the lowest possible radiation exposure to the patient. The possibility of genetic damage can be minimized by using a lead shield to protect the patient’s reproductive organs from X-rays. Radiographers and radiologists wear a film badge to monitor their exposure to radiation. (See also imaging techniques; radiography; radiology.)


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