Radiography - Contrast Shizz
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What is contrast?
Difference between densities/IR exposures.
What is dynamic range?
Concept of contrast on a monitor for digital imaging
Why do you need sufficient differences in exposure to image receptor?
- For pixels on the computer to exhibit different exposure values
- ( Remember contrast is difference between densities and IR exposure )
In long scale contrast, do you have more shades of grays or less shades of gray?
In long scale contrast, you have more shades of gray.
In short scale contrast, do you have more shades of gray or less shades of gray?
In short scale contrast, you have less shades of gray
Does short scale indicate an increase in contrast or a decrease in contrast?
Short scale indicates a INCREASE in contrast
The long scale contrast indicate an increase or a decrease in contrast?
Long scale indicated a DECREASE in contrast
What is RADIOGRAPHIC contrast?
Radiographic contrast is the total amount of contrast acquired from both the anatomical part and the film.
What is image receptor contrast?
- Range of densities that the film is capable of recording.
- ( It is also the slope in the D Log E Curve )
What four factors does Film Contrast depend on?
Film Contrast depends on intensifying screns, film density, d log e curve and processing.
What is the primary way of adjusting display contrast with digiital systems?
Changing the window with changes display contrast on digital systems.
What do most digital systme manufacturers do to their machines?
MAnufactureres calibrate the amount of radiation needed to take the radiographic image to provide a reasonable linear range of density/IR exposure
What does the histogram do?
The histogram assesses the range and quantity of IR exposure.
What is the LUT ( Look up table ) for?
Has a standard contrast for a selected exam that givces the desired image contrast for display.
Despite the ability of a digital system to provide proper contrast, what should you still do to other technical factors?
The receptor shoudl still receive teh correct amount of exposure in terms of mAs as well as kvP
What is subject contrast?
Range of differences in the intesnity of the x-ray beam after it has been attenuated by the subject.
What is subject cotnrast dependent on?
It is dependent on kvp adn the amount and type of irradiated material.
What is the primary controller of subject contrast?
kVp is the primary controller of subject contrast.
As kvp increases, what happens to the range of photon energies produced?
As kvp increases, theres a wider range of photon energies being produced.
What happens as the range of photon energies become wider?
As range of photon energies increase, theres a greater abiltiy of photons to penetrate through body tissue.
A wider range of photon energies leads to a wider range of density on film, which affects contrast how?
It shows overall lower contrast.
When difference between thickness of various part is greater, how is subject contrast affected?
subject contrast is increased.
When difference between average atomic number and adjacent tissues is great, what happens to subject contrast?
Subject contrast increases.
How does patient thickness influence contrast?
- A thicker subject will result in an increase in contrast
- A thinner subject will result in a decrease in contrast.
How does an increase in grid ratio affect contrast?
It increases the amount of contrast.
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