Unit 3: Scatter Control Flashcards
Scatter radiation is primarily the result of the _____________ ___________
Compton interaction
Scatter is produced ________ the pt
inside
Increased scatter adds _____________ ______
unwanted fog
In order to provide the best possible image, the radiographer must try to __________ the amount of scatter radiation reaching the IR
minimize
The two factors affecting the amount and energy of scatter are _______ and __________
kVp, irradiated tissue
kVp affects the ______________ of the beam
penetrability
The Amount of scatter radiation exiting the patient depends on ____
kVp
As kVp increases, _______ photons undergo interactions with matter
fewer
For the photons that do undergo interactions when kVp is increased, a greater percentage undergo _________ interactions
compton
Using higher kVp produces a ________ proportion of higher-energy scattered x-rays compared to lower kVp
greater
Larger the beam field size, the _________ the amount of scatter produced
greater
The thicker the part being imaged, the _______ the amount of scatter produced
greater
The higher the atomic number, the _______ the number of photoelectric absorption interactions
greater
The higher the atomic number, the ________ the scatter
lower
What produces white on image?
complete absorption
Bone absorbs _____ radiation and scatters ____ than soft tissue
more, less
How do we control scatter radiation? (3)
Beam-restricting devices
Grids
COLLIMATION
One purpose of beam restriction is to ____________________________
limit patient’s exposure
Purpose: beam restriction ____________ the amount of scatter radiation produced within the patient
reduces
Beam restriction is positioned right below the _____________________
tube housing
As beam restriction/collimation increases, field size ________
decreases
As beam restriction/collimation increases, patient dose __________
decreases
Decreasing field size, ____________ the quantity of scatter radiation
decreases
increase collimation, __________ image contrast
increase
increase field size, ___________ image contrast
decreases
What is a Flat piece of lead (diaphragm) that has a hole (aperture) in it?
Aperture Diaphragms
What is the simplest form of beam restriction device?
Aperture Diaphragms
Where are aperture diaphragms placed in relation to the x-ray tube?
directly below x-ray tube
What is the disadvantage to aperture diaphragms?
large area of unsharpness
What is essentially an aperture diaphragm that has an extended flange attached to it?
Cones and Cylinders
Where are cones and cylinders placed in relation to the x-ray tube?
directly below tube window
Are cones and cylinders interchangeable among tube housings?
no
Are cones and cylinders interchangeable among tube housings?
no
Which beam restriction device creates a circular projected field?
cones and cylinders
A cylinder is ________ at limiting un-sharpness
than a cone
better
When are cones and cylinders used?
Sinus exams
Lateral L5-S1 Projection
Nasal bones
Which beam-restricting device is used most often?
collimators
Collimators have __________ sets of lead shutters that change the size and shape of the primary beam
2-3
The entrance shutters within the collimators, limit x-ray beam much like the ____________ _________ would
aperture diaphragm
The lead/bottom shutters have the ability to ________________________
adjust the size of the field
Which shutters reduce the amount of off-focus radiation from reaching the IR by absorbing this radiation before it exits the tube?
upper
Which shutters reduce the penumbra along the periphery of the beam?
bottom
Parts to collimator box (3)
shutters
light source/mirror
plastic template w/ crosshairs
During a quality control check, the collimator misalignment should be less than ___ of the SID used.
2%
During a quality control check, the perpendicularity of the CR must be less than or equal to __ misaligned
1%
What was required by law for many years before it was no longer made as a requirement?
automatic collimators
automatic collimators make it difficult for the radiographer to increase the size of the primary beam to a field_________ than the IR
larger
When the beam is restricted, _______ scatter radiation will reach the image receptor, technical factors may need to be __________ to compensate for the reduction in the overall image receptor exposure
less, increased
Typically increased ________ of the mAs to compensate for the reduction in field size
25-50%
lead blockers and lead masks are considered ____________ devices
Ancillary
Which device helps absorb scatter that is produced in the soft tissue?
ancillary devices
Which device helps absorb scatter that is produced in the soft tissue?
ancillary devices
Digital IRs are ______ sensitive to lower-energy
levels of radiation
more
PBL
positive beam limitation
When making a significant increase in collimation, what should be increased?
mAs
