Rad Science contrast Flashcards
one of the 2 properties that make visibility of detail (photographic factor)
contrast
contrast is the difference between
adjacent densities
_contrast few shades of grey low kV short scale narrow latitude
High
_contrast many shades of gray high kV long scale wide latitude
low
what is the controlling factor of contrast
kV
kV and contrast have an _ relationship
indirect
as kV increases, contrast
decreases
_controls the amount of scatter produced. Increasing _ increases the possibility of scatter, decreasing contrast
kV
kV
increasing _ increases the average energy of the beam
kV
increasing _ increases more uniform penetration of parts by the shorter wavelength x-rays
kV
increasing _ increases the potential difference
kV
compton /scatter is what color
grey
PE is what color
white
increasing OID= better
contrast
distance- _ affects density using the air-gap technique. As your _ increases, there is less chance of scatter reaching the IR increasing
OID
OID
what changes the average energy of the beam
filtration
filtration makes the beam more
homogenous
raising the average energy is the same as raising the _ which raises the chance for compton interactions, thus reducing contrast
kV
collimating reduces the amount of tissue being irradiated, reducing the amount of Compton interactions possible, increasing contrast
beam restriction
as the part size increases, more chances for compton interactions, increasing scatter, reducing
contrast
additive diseases will _ subject contrast and increase radiographic contrast
increase
what removes scatter before it reaches the IR, improving contrast
grids
contrast improvement factor
k= contrast w/grid
——————-
contrast w/out grid
Grid ratio=
D
what is the formula for contrast improvement
k= contrast w/grid
——————
contrast w/out grid
as kV increases, contrast
decreases
as OID increases, contrast
increases
as grid ratio decreases, contrast
decreases
as filtration decreases, contrast
increases
as collimation decreases, contrast
decreases
as patient size increases, contrast
decreases
degree of geometrical sharpness or accuracy of the structural lines actually recorded on the image
detail
Detail is also known as
definition
sharpness
spatial resolution
recorded detail
unit of resolution is
line pairs per millimeter
there is always some loss of _ on all images
detail (sharpness)
for optimal detail eliminate reduce reduce reduce Increase
motion OID focal spot size intensifying screen, phosphor size & concentration SID
factors affecting recorded detail and formula
Distance
SOD =OID=SID
OID decreases, detail
increases
SID increases, detail
increases
use a large _ to compensate for a large OID ex; C-spine
SID
sharp shadow around object
umbra
unsharp shadow around object (focal spot blur)
penumbra
as focal spot size increases, penumbra _, detail _
increases
decreases
as film/screen speed is decreased, detail
increases
as film/screen speed increases, detail
decreases
if the total # of incident photons reaching the intensifying screen are insufficient to activate enough phosphors to emit light over the entire radiograph
quantum mottle
quantum mottle is caused by low
mAs
_ is the only way to fix quantum mottle; grainy appearance
mAs
There must be good contact between the film and intensifying screen. Poor contact makes bad resolution. Cassette must be discarded
wire mesh test
3 types of motion
pt. motion
tube motion
excessive reciprocating grid motion
voluntary motion (breathing) can best be controlled by
communication
Involuntary motion (peristalsis, heartbeat) can be best controlled by a _ and _ to maintain density
short exposure time
increased mA
as motion decreases, detail
increases
as OID increases, detail
decreases
as SID decreases, detail
decreases
as focal spot size decreases, detail
increases
as phosphor size increases, detail
decreases
as film/screen speed decreases, detail
increases
misrepresentation of the size or shape of the structures being examined
distortion
2 kinds of distortion
size-mag. OID/SID
shape-elongation/foreshortening
as size magnification decreases, detail
increases
to minimize size distortion, max. _ and min. _
SID
OID
as SID increases, distortion
decreases
as OID decreases, distortion
decreases
shape distortion can be
elongation
forshortening
elongation is caused by the
tube or IR improperly aligned
foreshortening is caused by the
prt. being improperly aligned
The CR should be _ to the part and IR
perpendicular
The CR is the only portion of the beam w/out
shape distortion
as SID decreases, distortion
increases
as OID decreases, distortion
decreases
as tube alignment decreases, distortion
increases
as IR alignment increases, distortion
decreases
as part alignment increases, distortion
decreases
