Scatter Radiation Flashcards
Factors that influence scatter
kVp, patient size, field size
Source of occupational exposure
Compton scatter
As ___ increases, Compton interactions also increase
kVp (energy)
T/F: Modern digital filming is more sensitive to scatter than older filming modalities
True
T/F: Field size and collimation are inversely related
True
Automatic collimators use ____ to match the light field with the cassette size
Positive beam limiting (PBL)
Go on the tube head/window to limit the beam coming out
Aperture diaphragm
“Cleans up” scatter radiation using lead strips that absorb scattered x-rays
Grids
Use of a grid requires more ___
mAs
Increase in patient size [increases/decreases] amount of scatter
increases
Grid Ratio =
h/D
(h= height of lead strips)
(d= distance between them)
Use of a grid is recommended for anatomy greater than:
4 inches (10 cm) thickness
Number of lead lines per unit length
Grid frequency
T/F: The higher grid frequency, the more distinct grid lines on x-ray image
False
Two types of grid patterns:
Cross-hatched and linear
An aperture diaphragm that has an extended flange attached to it
Cone/cylinder
The orientation of the lead lines relative to one another
Grid focus
Grid conversion factor =
mAs with grid / mAs without grid
A decrease in the number of transmitted photons that reach the IR because of some misalignment of the grid
Grid cutoff
Occurs when using an SID outside the recommended focal range
Off-focus grid cutoff
Concept that much of the scatter will miss the IR if there is an increased distance between the patient and the IR
Air gap technique
mAs should be increased __% for every centimeter of air gap
10
A beam-restricting device that has two or three sets of lead shutters is a(n):
Collimator
A device consisting of very thin lead strips with radiolucent interspaces intended to absorb scatter radiation emitted from the patient is a:
Grid
A larger the x-ray beam field size results in:
increase in scatter produced and increase in fog
T/F: As collimation decreases, exposure to the IR increases.
True
Changing from an 8:1 grid to a 12:1 grid, along with making the appropriate adjustments, will result in:
A: an image with increased contrast
B: using more mAs
C: Increased patient dose
A, B, and C
T/F: Digital IRs are not sensitive to scatter radiation
False
Grids that move during the exposure:
are reciprocating grids and are part of the Potter-Bucky diaphragm
If an excellent knee radiograph is produced using 10 mAs and an 8:1 ratio grid, how much mAs will be needed if no grid is available?
2.5 mAs
T/F: Placing a lead shield behind the patient’s lower back during lumbar spine imaging absorbs the scatter and reduces the amount striking the IR.
True
Significant collimation requires an increase of _____________ of the mAs.
30 - 50%
The most common cause of grid cutoff is due to:
off-level misalignment.
The unrestricted primary beam produces a(n) _________ area of exposure.
round
What is the grid conversion factor for a 12:1 ratio grid?
5 x
Why does the air-gap technique work?
The scatter photons are more likely to miss the image receptor.
T/F: A good alternative to collimation is electronic masking.
False
A larger field size will result in ___ scatter production
Increased
An increase in collimation results in a [increase/decrease] in radiographic contrast
Increase
When making a significant increase in collimation, _____ should be increased
mAs
The purpose of a grid in radiography is to:
Increase image contrast
With which one of the following grids would a convergent line be formed if imaginary lines from its grid lines were drawn in space above it?
Linear focused
With exposure technique compensation, which of the following would result in the greatest radiation exposure to the patient?
a 12:1 grid ratio
Off-focus grid cutoff occurs by using an SID that is not:
within the focal range of the grid
Which of the following are tools that the radiographer can use to limit scatter radiation?
beam-restricting devices and radiographic grids
What purpose does positive beam limitation serve?
To reduce patient exposure by limiting the exposure field to the same size as the image receptor in the Bucky tray
As beam restriction increases:
a. less volume of tissue is irradiated and higher image contrast
b. less scatter is produced and higher image contrast
c. less scatter is produced and less volume of tissue is irradiated
d. all options are correct
D
Which of the following is not a way to reduce the production of scatter radiation?
a. Reduce the tissue thickness.
b. Reduce the exposure field size.
c. Increase collimation.
d. Increase the grid ratio.
D
What is the result of imaging a thicker part or patient?
More Compton interactions
