Unit 4 Flashcards
Image Contrast
the degree of difference between the light and dark areas of a radiograph
What makes blacks, whites, and grays?
differential absorption
Subject Contrast
the component of image contrast determined by the size, shape, and x-ray attenuating characteristic of the subject who is being examined and the energy of the x-ray beam
What controls subject contrast?
kVp
What is the process that produces subject contrast?
Differential Absorption
Differential Absorption
the difference between the x-ray photons absorbed and those that penetrate the body
Attenuation
removal of any photons from the primary beam before striking the image receptor
Causes or attenuation
Patient absorption
Compton scatter
differential attenuation
a form of primary beam attenuation specific to patient absorption and compton scatter
Absorption
refers to x-ray photons that are attenuated by the body and do not reach the IR
Transmission
refers to x-ray photons that pass through the body and reach the IR
Primary Beam
the x-ray beam as it is upon exiting the collimator and exposing the patient
Remnant Beam
the x-ray beam that remains after interaction with the patient and that is exiting the patient to expose the IR
What is the remnant beam composed of?
transmitted photons and scattered photons
Radiopaque
body structures that readily absorb x-ray photons
(bones)
Radiolucent
less dense body structures that have much lower probability of absorption
(air-filled lungs)
Photoelectric Effect
absorption
How is absorption represented radiographically?
white
How is transmission represented radiographically?
black
What are the various shades of gray caused by?
tissues of the body where photons aren’t completely absorbed or transmitted
High contrast
large differences in brightness (B/W) on a radiograph
What is brightness?
exposure
What “scale” is high contrast?
Short Gray-Scale
Does short gray scale have more B/W or more Gray?
More B/W.
Only a few grays
A decrease in kVp results in _____ contrast and _____ gray scale.
A decrease in kVp results in high contrast and short gray scale.
An increase in kVp results in ______ contrast and _____ gray scale
An increase in kVp results in low contrast and long gray scale
low contrast
small differences in brightness on a radiograph
What “scale” is low contrast?
Long gray scale
Does long gray scale have more b/w or more gray?
More gray
Some b/w
What term describes the total number of differences in brightness levels that are visible on a radiograph?
Gray Scale
Bit Depth
total brightness levels that an imaging monitor is capable of displaying
8 factors affecting image contrast
- x-ray beam quality (kVp)
- differential absorption (subject contrast)
- Computer processing and display
- filtration
- compton scatter
- radiographic grids
- OID
- beam restriction
high kvp = ___ contrast
high kvp = low contrast
low contrast = _____ gray scale
long
8 factors: kVp
increasing kvp _____ pentrability
increases
8 factors: kVp
a greater percentage of the beam passing through the patient = a ____ percentage of differential absorption
decreased
8 factors: kVp
a decreased percentage of differential absorption = ____ gray scale, and ___ image contrast
long gray scale
low image contrast
8 factors: kVp
decreasing kvp = _____ penetrability
decreased
8 factors: kVp
a decreased percentage of beam passing through the patient = ____ percentage of differential absorption
increased
8 factors: kVp
an increased percentage of differential absorption = ____ gray scale, and ____ image contrast
short gray scale
high image contrast
Contrast is the percentage of _______ vs. ______
absorption vs transmission
8 factors: differential absorption
higher levels of differential absorption = ____ black and white
more
8 factors: differential absorption
increased differential absorption = ____ subject contrast, and ____ gray scale
high subject contrast
short gray scale
8 factors: differential absorption
decreased differential absorption = ____ subject contrast, and ___ gray scale
low subject contrast
long gray scale
8 factors: differential absorption
more matter =
more scatter
is scatter diagnostic?
no
Scatter has what effect on contrast?
decreases contrast
8 factors: Computer processing and display
Look Up Table (LUT)
primary controlling factor in image contrast
8 factors: Computer processing and display
when does the LUT take place?
after the exposure is made and the image is being processed by the imaging system software
8 factors: filtration
filtration
removes low energy photons from the x-ray beam
8 factors: filtration
an increase in filtration = a _____ in contrast
decrease
filtration and contrast have what type of relationship?
indirect
8 factors: filtration
an increase in filtration = a _____ in differential absorption
decrease
8 factors: filtration
a decrease in filtration = a ____ in differential absorption
increase
8 factors: filtration
a increase in filtration = a ____ in differential absorption
decrease
8 factors: compton scatter
compton scatter
an x-ray photon that interacts with the body and then scatters off of its original trajectory
8 factors: compton scatter
does compton scatter contribute useful information
no
8 factors: compton scatter
what does compton scatter do to image contrast?
decreases
