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Digital X Ray

Digital X Ray


X-ray technology provides physicians and technicians with a noninvasive method for seeing inside objects. In the case of a patient's body, this may allow diagnosis of disease or injury without surgery. Both conventional and digital x-ray methods employ high voltage electronic tubes such as synchrotons that emit very short wavelength, high energy electromagnetic radiation in the range of 1011108 meters (3.28 × 10103.94 × 106 feet) (a frequency of about 3 × 1019 Hz to 3 × 1016 Hz). One Hz (Hertz) is equal to 1 cps (cycle per second).

Unlike longer-wavelength, lower-frequency visible light, x-ray radiation consists of waves so small that they can pass through solid materials with little effect. As the radiation moves through materials of different densities (bone and tissue, for example), some waves are blocked and produce shadows that result in light-and-dark images. Some materials, such as bone or metal, are opaque and appear as light areas, while other materials such as air in body cavities allow most of the x-ray waves to pass through, producing dark areas in the image.

Conventional x-ray images are captured by special photographic film, sensitized with silver salts that are converted by developing processes to dark and light images. Photons striking a photographic emulsion convert some silver ions to tiny particles of silver that grow large enough during the process of developing to form tiny grains in the photographic negative. Digital x-ray processes use individual crystal photodiode assemblies (each photodiode acts as a very small light-sensitive transistor, using the light energy from individual photons to modulate an electrical current flowing through the diode) containing compounds such as cadmium tungstate or bismuth germanate to capture light energy as electrical pulses that are then converted from analog to digital signals, stored in computer memory, and processed to form visual images on computer screens. Because electronic sensors may be more sensitive than film, digital x-ray processes may use as little as 10 percent of the energy needed for conventional x rays (and may thus require less massive shielding).

Although different types of x-ray technology may be ideally suited to different applications, the use of electronic sensors and digital technology offer several advantages over conventional x rays. The capture of an image by a photosensitive electronic device is rapid and allows the image to be enlarged, colored, or adjusted in density. In addition, the use of electronically captured images may be less expensive, allowing computer-assisted data processing and storage. Conventional x-ray film must be developed, washed, fixed, and dried, requiring chemical substances that may be harmful to the environment, and the resulting images on film may require massive storage facilities.

Digital x rays can be modified electronically to increase contrast, display certain structures in color or three dimensions, or subtract areas that interfere, allowing clearer pictures of structures such as veins and arteries. Very small differences in density may be amplified for even clearer viewing. This may be important in cases in which a contrast medium is injected into veins or arteries; enhancing small differences allows the use of smaller amounts of the contrast medium, lessening the danger to patients.

After digital x-ray images have been obtained, they may be easily copied, displayed, stored electronically, shared with patients, or sent to remote locations for examination by highly trained technicians. The images may be conveniently linked to other equipment or processes such as CAT (computer axial tomography) scans or three-dimensional displays. Digital technology may also be employed in security applications for the remote scanning of packages and luggage.

see also Selenium.

Dan M. Sullivan

Bibliography

Bushnong, S. C. (2001). Radiologic Science for Technologists. St. Louis, MO: Mosby.

Wolbarst, A. B. (1993). The Physics of Radiology. Norwalk, CT: Appleton and Lange.

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