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30 Cards in this Set
- Front
- Back
Two photographic factors allow detail to be seen
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Density
Contrast |
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Window width
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The digital processing that produces changes in the range of density/brightness which is used to control contrast.
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High Contrast
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Few shades of gray
Increased contrast Low kVp Short scale contrast Short (narrow) dynamic range/window width |
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Low Contrast
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Many shades of gray
Decreased contrast High kVp Long scale contrast Large (wide) dynamic range/window width |
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contrast
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the number of useful visible densities or shades of gray.
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Physical contrast
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- total range of density values recorded by the receptor
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Visible contrast -
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total range of density values perceived by the human eye in an image.
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Compression or expansion of range of visible densities
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Change in D log E curve of film
Adjustment to kVp Adjustment of window width |
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Image Receptor Contrast (Film Contrast)
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Intensifying screens
Film density D log E curve Film processing |
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Subject Contrast
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Kilovoltage
Amount of irradiated material Type of irradiated material |
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Film contrast
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- range of densities film can record
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film contrast Dependent on four factors
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Intensifying screen
Film density Slope of D log E curve Processing |
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Directly exposed film has
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lower contrast than screen film
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Excessive or inadequate density
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decreases contrast
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Contrast is affected by
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composition of the emulsion, as the slope of the curve gets steeper the contrast increases
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The primary method for adjusting contrast with digital imaging systems is
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Window Manipulation
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Subject contrast
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The degree of differential absorption resulting from the differing absorption characteristics of the tissues in the body.
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Wider range of photon energy as kVp increases
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Greater penetrability
Greater range of exposures Greater amount of scatter Longer scale of contrast |
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As a result of increased scatter, contrast is
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decreased
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Scatter raises
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the base plus fog (Toe) and decreases the slope of the curve
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Any factor that increases fog, decreases contrast
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-heat to film
-chemicals… -processing |
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Increase in thickness and field size
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Increase scatter
Longer scale of contrast |
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High atomic number and tissue density
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Greater attenuation
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Large difference in atomic number and tissue density of adjacent tissues
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High contrast
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Contrast mask
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a tool to help focus on contrast in a selected area
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Kilovoltage
Inversely related |
As kVp increases, contrast decreases
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Focal Spot Size
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Does not influence contrast
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Anode Heel Effect
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Little effect on contrast
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Increased filtration
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Increased average beam energy
Decreased contrast |
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Chemical fog
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Decreases slope of the D log E curve
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