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30 Cards in this Set

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