CH 27 Contrast & CH18Grids Flashcards
Visibilty of detail
Image is visible to the human eye only because contrast permits it.
Image contrast
difference between adjacent densities/IR exposures
Subject contrast
in patient, differential absorption differences in densities.
Window width
Manipulating the contrast on digital systems
Contrasts main controlling factor?
kV
Larger differences between densities means
High contrast (less gray)
In regards to contrast what happens when kV decreases?
Contrast increases/High Contrast
High contrast means that the image has?
less densities, shorter scale
In regards to contrast what happens when kV increases?
Contrast decreases/Low contrast
Low contrast means the image has?
More denities, scale is longer
In regard to bone work what would kV be?
Lower to moderate kV.
Short scale is the same as?
High Contrast
Long scale is the same as?
Low contrast
In regards to soft tissue what would kV be?
Higher kV
Subject contrast
dependent on the amount of kV, type of tissue and tissue thickness
Use of a grid leads to
higher contrast, removes sctter, less densities, shorter scale, higher contrast
An increase of ___% (____kv) at 30-50kV will lead to a visible change?
4-5%, 1-3
An increase of ___% (____kv) at 50-90kV will lead to a visible change?
8-9%,4-8
An increase of ___% (___kv) at 90-130kV will lead to a visible change?
10-12%, 9-16kv
15 percent rule
Increasing kV by 15% will increase the density 2xs. Decreasing it by 15% will cut denisty in half.
Film base is made of
polyester that pocesses an inherent blue dye and fog.
Latitude is
The range of densities that can be viewed on the radiograph.
The geometric factors for detail are?
FSS (Focal Spot Size), SID (Source to IR Distance) and OID (Object to IR Distance).
What kinds of screens are there? (In order from slowest to fastest)
1)Nonscreen, 2)Slow/Detail/Extremity 3)Medium/Par 4)Fast/High speed
