image quality factors Flashcards
contrast affected by…
- kVp
- OID
- grids
- filtration
- patient size
OID affect on contrast
- small OID causes more scatter to hit IR
- large OID causes less scatter to hit IR (because it’s absorbed in air before it hits IR)
up OID
= down scatter
= up contrast
grids affect on contrast
-increased grids mean less scatter hitting receptor
up grid ratio
= down scatter
= up contrast
collimation affect on contrast
-tighter collimation means less scatter hitting receptor
tighter collimation
= down scatter
= up contrast
filtration affect on contrast
-lower kVp photons are filtered out, so beam is stronger
up filtration
= down differential attenuation
= down contrast
subject contrast
the magnitude of the signal difference int he remnant beam as a result of the different absorption characteristics of the tissues and structures making up the part
spatial resolution affected by…
- motion
- focal spot size
- OID
- SID
OID affect on spatial resolution
short OID = up spatial resolution
more room for divergence of the beam
SID affect on spatial resolution
long SID = up spatial resolution
photons stay more aligned as they pass by object (less divergence of beam)
Focal spot size affect on spatial resolution
small FSS = up spatial resolution
photons will remain more aligned when passing object (photon alignment from many different points on focal spot causes more unsharpness)
Focal spot blur calculation
OID
blur = FSS x ———-
SOD
spatial resolution also affected by…
- DEL size
- DEL pitch
- pixel size
- pixel pitch
- matrix size
Exposure affected by…
mAs, kVp
SID, grid ratio, patient size, pathology, filtration, collimation, heel effect
magnification factor formula
SID
MF = ——–
SOD
three ways distortion occurs
- misalignment of tube
- misalignment of part
- angling of receptor
