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chap 27 contrast


What classifies an image as "high contrast" differences between the adjacent densities that comprise contrast are great. (fewer shades of gray..)
What makes an image "low contrast' When differences in adjacent densities are minimal. (has more shades of gray)
define dynamic range the concept of contrast as it is displayed on a soft-copy monitor for digital images.
Scale of contrast is? # of useful visible densities or shades of gray.
Short scale contrast? image that demonstrates considerable or maximal differences between densities and has a minimal total number of densities. (short scale is high contrast)
Long scale contrast? image that demonstrates slight or minimal differences between densities but has a maximal total number of densities. (long scale is low contrast)
Physical contrast? total range of density values recorded by the IR. It is the maximum contrast possible and most accurate representation.
Visible contrast? total range of density values that can be perceived by the human eye in a single image.
Radiographers manipulate the ____ contrast available into the ____ range to produce the diagnostic image. physical, visible.
What is the primary method for adjusting display contrast with digital imaging systems? with window width manipulation.
In what ways can you manipulate contrast? Change in D log E curve of film Adjustment to kVp Adjustment of window width
Film contrast depends on what four things? Intensifying screen Film density Slope of D log E curve Processing
What post-processing factors affect the final digital image receptor contrast? Histogram and LUT (look up table)
What is subject contrast? Range of differences in the intensity of the x-ray beam after it has been attenuated by the subject.
What is subject contrast dependent on? Kilovoltage Amount of irradiated material Type of irradiated material
What is the primary controller of subject contrast? kVp.
What are the two controlling factors of contrast? kVp and pulses by the generator.
Increasing # of pulses by generator waveform causes contrast to what? decrease.
Increasing OID causes contrast to what? Increase.
Increasing filtration causes contrast to what? Decrease. Increase filtration, increase beam energy, higher beam causes more scatter, scatter decreases contrast.
Increasing collimation causes contrast to what? Increase. The smaller the IR and closer the collimation, the less photons, which is less scatter.
Additive pathological conditions cause contrast to what? Decrease.
Increasing grid ratio causes contrast to what? Increase. Grids absorb scatter, increasing contrast.
Increasing SID causes contrast to what? SID has no effect.
High contrast is high or low energy? Low energy.
Low contrast is high or low energy? High energy.
Attenuation is what? Reduction of # of photons in beam as it passes though the patient. ex) bone attenuates more than the lungsā€¦ has higher/more attenuation.
High frequency generators have what kind of ripple? Less than 1% ripple. This is most efficient.
ei means? Exposure index.
Created by: Zoest35