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Radiology

Chapter Four

TermDefinition
Contrast The visual differences between shades ranging from black to white in adjacent areas of the radiographic film.High kilovoltage produces a radiograph with long-scale contrast. Low kilovoltage produces a radiograph with short-scale contrast.
Crystal Term used to refer to the silver halide combinations that are present in the film emulsion. Larger crystals require less radiation exposure to produce an image. However, larger crystal size may result in slightly less image resolution.
Definition Sharpness and clarity of the outline of the structures in a radiographic image. Poor definition is generally caused by movement of the patient, film, or the tube head during exposure.
Density The overall darkening or blackening of the radiographic image as determined by the amount of light transmitted through a film. The way to change the density of a radiograph is to change the milliamperage and exposure time (milliampere/second).
Exposure Time The time interval, expressed in seconds or impulses, that x-rays are produced.
Film Contrast See Contrast.
Focal Spot Small area on the target on the anode toward which the electrons from the focusing cup of the cathode are directed. X-rays originate at the focal spot.
Intensifying Screen Plastic sheet coated with calcium tungstate or rare earth fluorescent salt crystals. Positioned in a cassette. When exposed to radiation, the fluorescent salts glow, giving off a blue (calcium tungstate) or green (rare earth) light.
Inverse Square Law States that the intensity of radiation is inversely proportional to the square of the distance from the source of the radiation to the point of measurement.
Long-Scale Contrast Low-contrast image. A radiographic image with many shades of gray. Produced with high kilovoltage.
Object Film Distance Distance between the object being radiographed and the film.
Penumbra Partial shadow or fuzzy outline around the image.
Radiographic Contrast See Contrast.
Radiolucent That portion of the radiograph that is dark. Structures that lack density permit the passage of x-rays with little or no resistance. These structures appear dark on the image.
Radiopaque That portion of the radiograph that appears light. Dense structures resist the passage of radiation. These structures appear light on the image.
Short-Scale Contrast High-contrast image. A radiograph that exhibits black and white with few shades. Produced with low kilovoltage.
Target-Film Distance (source–film distance) Distance between the focal spot on the target and the recording plane of the film.
Target-Object Distance (source–object distance) Distance between the focal spot on the target and the object being radiographed.
Created by: daisenmurray