Roentgenography

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roentgenography

[‚rent·gə′näg·rə·fē]
(physics)
Radiography by means of x-rays.

Roentgenography

 

(also skiagraphy), in medicine, X-ray analysis in which an X-ray image of an object, or a roent-genogram, is produced on photographic film; one of the main methods of roentgen diagnosis. The X-ray photographing of any organ is performed in at least two mutually perpendicular directions. The technical conditions for photographing are determined by means of tables or are automatically provided during roentgenography by special X-ray instruments. Roentgenograms reveal more details of an image than are revealed during roentgenoscopy. The radiation load is lower during roentgenography. The photograph obtained is a document that is stored at the medical institution and compared with subsequent roentgenograms.


Roentgenography

 

the photographic or video tape recording of the shadow image of various objects, obtained when the objects are irradiated with X rays; the image depicts the internal structure of the objects. Roentgenography is used in medicine, biology, physics, and technology and by the military. The objects studied include internal organs and systems in man and animals, plants, industrial products, structural elements, and specimens of various substances. Roentgenography is carried out either by the direct method, in which a photosensitive material is exposed directly by X rays passing through the object being photographed, or by the indirect method, in which the image of the object formed by X rays on a fluorescent screen is rephotographed on motion-picture film or is recorded on magnetic tape.

Roentgenography by the direct method uses X-ray film, a special type of photographic film characterized by very high contrast with comparatively high sensitivity to X rays. The film is loaded into a cassette placed behind the object being irradiated. In order to reduce the exposure, amplifying fluorescent screens placed on both sides of the film in direct contact with its emulsion layers are also used. In motion-picture roentgenography by the direct method, the object is irradiated only during the period of exposure of the frame in order to avoid loss of image sharpness resulting from film advance. For this purpose, current impulses from a switch driven by the camera’s film-transport mechanism are fed to the control grid of a three-electrode X-ray tube. As the film winds from reel to reel during filming, the section being exposed is bent around a smooth, rotating drum covered with a fluorescent layer that serves as the amplifying screen. Frame exposure times of 10-7 sec at a film speed of 100 frames/sec can be achieved in this way using a field-emission X-ray tube.

In roentgenography by the indirect method, the image formed by the X rays appears on a fluorescent screen with a yellow-green or green glow; the image is photographed by means of a still or motion picture camera using special fluorographic film with a high sensitivity to light in the yellow-green region of the spectrum, or it can be recorded with a video tape recorder. Screens with a fluorescent film applied to a metal plate and covered with a thin metal film on the outside are used to increase image brightness. When a direct voltage is fed to the metal film and plate, the brightness of the screen is increased approximately tenfold. Significantly greater increases in brightness are achieved by incorporating image converters in the circuitry of the roentgenographic equipment. In such units, the X rays strike the photocathode of the image converter after passing through the object, and the image produced on the screen of the converter is rephotographed by a still or motion-picture camera. In motion-picture roentgenography using the indirect method, in the simplest case the object is irradiated continuously during the entire period of filming. However, in most modern roentgenographic motion-picture units the radiation is generated periodically—only during exposure of the frame. Because of this, in many cases, especially in units with image converters, the intensity of the X-radiation can be kept within the limits of the permissible norms for irradiation of biological objects. This type of roentgenography is used extensively in roentgen diagnosis. In photographing technical objects, where the intensity of X-radiation does not play a significant role, the frequency of pulsed roentgenography may reach 1,000 frames/sec.

REFERENCE

Bajza, K., L. Henter, and S. Holbok. Rentgenotekhnika. Budapest, 1973. (Translated from Hungarian.)

A. A. SAKHAROV