RAD 205 contrast
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34 Terms
The difference between adjacent exposures
Contrast
Is the range of differences in the intensity of the x-ray beam after it has been attenuated by the subject
Subject contrast
Subject contrast depends on
Amount of irradiated material
Type of irradiated material
Amount of irradiated material
Dependent on thickness of part and field size
Increase in thickness and field size
Increase in thickness and field size causes
increase scatter
longer scale of contrast
Type of irradiated material
influenced by atomic number and tissue density
high atomic number and tissue density
large difference in atomic number and tissue density of adjacent tissues
high atomic number and tissue density leads to what
greater attenuation
Large difference in atomic number and tissue density of adjacent tissues lead to what
high contrast
kVp and subject contrast leads to increase kVp which leads to wider range of photons which leads to
greater penetrability
greater range of exposure
greater amount of scatter
longer scale of contrast
Primary controller of contrast
kVp
increased kvp
Decrease contrast
kVp also controls the amount of scattered produced an increase in kVp casues
increase scatter produced → increase fog → decrease contrast
Increase in Focal spot size, anode heel effect, film screen
negligible effect
Increase mAs
negligible effect
Increase SID/OID
Increase contrast
How does increasing OID affect contrast
decreases the scatter reaching the IR therefore increasing contrast
Increase Filtration
decrease contrast
Increase beam restriction / collimation
increase contrast
Increase Anatomical Part
decreases contrast (causes a lot of scatter)
Increase grids
increase contrast (takes away scatter)
Increase SOD
Increase contrast
Increase tissue density
increase contrast
increase destructive pathology
increase contrast
increase additive pathology
decrease contrast
increase motion
negligible effect
kVp is…. to exposure
direct but not proportional
Low kvp=
….contrast
….scale
….frequency
….wavelength
…..dynamic range
high contrast
short scale
Low frequency
long wavelength
narrow dynamic range
if SID is tripled what change must be made in order to maintain exposure
increase 9x
The result of differences in transmission of the beam as it passes through the patient resulting in signal differences to the digital detector
differential attenuation
The concept of contrast as it is displayed on a soft-copy monitor for digital images; range of density/ brightness of the display monitor light emission
dynamic range
The number of shades of gray in a radiographic image
grayscale
The total amount of contrast acquired from the image receptor
image receptor contrast
The number of useful visible densities or shades of gray
scale of contrast
The digital processing that produces changes in the range of density/brightness, which can be used to control contrast.
window width