Unit 3 (Filtration & Beam Restriction)
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Unit 3 (Filtration & Beam Restriction)
Unit 3: Chapter 10 (Filtration) and Chapter 15 (Beam Restriction)
the process of eliminating undesirable low energy x-ray photons by the insertion of absorbing materials into the primary beam
what does filtration allow the radiographer to do?
shape the emission spectrum
if you increase filtration, does exposure to the patient increase or decrease?
if you increase filtration, does the overall average energy of the beam increase or decrease?
what is another name for increasing overall average energy?
"hardening" of the beam
low energy ranges will contribute to an increase or decrease in patient dose?
soft tissue penetration requires around ________ keV photons.
_____________ photons cannot penetrate the part.
what type of energy only contributes to patient dose?
___________ is mostly used for patient advantage.
what is the standard filtering material?
filtration is expressed as:
aluminium equilvalency (Al/Eq)
when using 70 kVp or above, the law requires a minimum of _______ filtration.
2.5 mm of Al/Eq
the law requires a minimum of 2.5 mm Al/Eq filtration when using _____ kVp or above?
filtration needed to reduce the beam to one half of it's original intensity.
half-value layer (HVL)
name the 5 types of filtration
filtration that cannot be controlled as it is part of the x-ray tube.
name the 3 parts that make up inherent filtration
glass envelope (pyrex glass)
dielectric oil bath
glass window of the housing
silver on the mirror is equivalent to _______.
1 mm Al/Eq
tube aging increases or decreases inherent filtration?
__________ coats the tube window over time.
as vaporization increases, does the HVL increase or decrease?
does it take more or less HVL to decrease the beam to half of its intensity as vaporization increases?
any filtration outside the tube and housing
a collimator is an example of ________ filtration.
a collimator typically provides _________ filtration.
1 mm Al/Eq
the collimator Al/Eq of 1 mm is due to:
silver on collimator mirror
what is the function of the collimator mirror and what angle is needed?
it projects light out of the tube housing
filtration made of two or more materials
another name for compound filtration is:
the K-shell refers to what?
the inner shell of the atom
the order of layers in compound filtration are most often:
tin has an atomic number of:
the characteristic produced by tin is about _______ keV.
copper has an atomic number of:
_________ absorbs the 29.3 keV characteristic produced by tin.
the characteristic produced by copper is about _______ keV.
aluminium has an atomic number of:
___________ absorbs the 8 keV characteristic produced by copper.
the characteristic produced by aluminium is about ________ keV.
the 1.5 keV characteristic produced by aluminium is absorbed by:
is the material with the highest Z# closer to the source or the part?
in compound filtration each layer absorbs the characteristic photons created:
in the previous layer
compound filtration is used with high or low energies?
filtration that evens radiographic density with parts that have uneven tissue thickness or densities.
name two examples of compensation filtration.
in compensation filtration, a wedge is used most often for:
in compensation filtration, a trough is used most often for:
the _________ portions of the trough and wedge absorb more radiation.
for the wedge compensation filter on the foot, the thick end is at the toe or the heel?
the thicker portion of the wedge filter causes the density to be more or less in the toe region?
the filtration that includes both inherent filtration and added filtration
total filtration does or does not account for compound and/or compensating filtration?
total filtration example: if the inherent filtration is 3.5 mm of Al/Eq and the added filtration is 1 mm of Al/Eq, what is total filtration?
4.5 mm of Al/Eq
only low energy photons are removed by filtration. true or false?
when high energy photons are removed due to filtration, it results in an increase or decrease in radiographic density?
when radiographic density is decreased due to high energy photons removed by filtration, you must compensate with:
an increase in technique
increase filtration, increase or decrease density?
increase filtration, increase or decrease intensity?
what piece of equipment is used to measure filtration?
when measuring filtration with an ionization chamber, filtration is measured in:
ionization in air
in the field, an ionization chamber is used for:
calibration of equipment
does a single phase x-ray tube or a three phase x-ray tube require a greater HVL?
three phase (because it gives off more energy)
As kVp increases, does scatter increase or decrease?
Name two factors that affect the volume of irradiated material.
As field size increases, does scatter increase or decrease?
As the thickness of the patient increases, does scatter increase or decrease?
What factor affects the penetrability of the beam?
Does a higher kVp increase or decrease the chances of penetration of the part?
With low kVp, is there an increase or decrease of photoelectric absorption?
If kVp is increased, is there an increase or decrease of transmittion?
If kVp is increased, is there an increase or decrease in photoelectric absorption?
If kVp is increased, is the amount of Compton scatter increased or decreased?
If kVp is increased, does patient dose increase or decrease?
Typically, is an increase in kVp accompanied by an increase or decrease in mAs?
If kVp is increased, is the scale of contrast longer or shorter?
What are the two ways in which patient dose is increased by decreasing kVp?
photoelectric absorption is increased which adds to patient dose
decreased kVp is usually accompanied by increased mAs which adds to patient dose
If kVp is decreased, is the scale of contrast longer or shorter?
If the field size increases, does the volume of tissue increase or decrease?
If the field size increases, does the amount of scatter increase or decrease?
If the field size increases, is the scale of contrast long or short?
If there is an increased patient thickness, does the amount of scatter increase or decrease?
If there is an increased patient thickness, does the scale of contrast get longer or shorter?
If field size decreases, does the number of photons reaching the IR increase or decrease?
If field size is decreased, does image receptor exposure increase or decrease?
To maintain IR exposure after an increase in mAs, what must happen to the field size?
a significant reduction
Do parts with higher atomic numbers have increased or decreased scatter?
In what modality of radiology are compression devices most utilized?
Do compression devices increase or decrease spatial resolution?
Name three benefits of using a compression device:
decrease in patient thickness
lowers patient dose
brings tissue closer to film (decreases OID)
Name four reasons we use beam restrictors to decrease field size:
decreases unnecessary tissue exposure
shortens the scale of contrast
increases the visibility of detail
Name four types of beam restrictors:
Cone or cylinders
What is the simplest type of beam restrictor?
What is an Aperture Diaphragm?
A lead or lead-lined plate attached to the x-ray tube
Name three examples of equipment that aperture diaphragms are made for:
dedicated chest or head units
What device is made for use in fixed applications with a fixed IR and fixed SID?
Does penumbra increase or decrease when the beam restrictor is closer to the object being imaged?
Does penumbra increase or decrease with the use of an aperture diaphragm?
With the use of an aperture diaphragm, does off-focus radiation increase or decrease?
Does penumbra increase or decrease when the diaphragm is closer to the focal spot?
When using an aperture diaphragm, what must you be careful of when you apply it?
that you place the diaphragm and the tube in the same orientation to prevent aperture cuttoff
How do you determine the field size of a diaphragm?
Image Size = (SID x diaphragm diameter)/ distance from focal spot to diaphragm
What device is considered to be a variation of the aperture diaphragm?
extension cones and cylinders
Do extension cones/cylinders increase or decrease penumbra?
What beam restrictor device is the same size all the way down?
What beam restrictor device flares out and allows divergence?
Does the use of a cylinder/cone increase or decrease scatter?
Does the use of a cylinder/cone increase or decrease detail?
When you use a cone, you must center carefully to avoid:
Name three examples of when you might employ the use of cones/cylinders:
head work (sinuses or skulls)
spine work (spot films)
What unit came with cone and cylinder attachments?
the Franklin Head Unit
How do you determine field size with circular cones?
Image Size = (SID x lower diameter of cone)/ distance from focal spot to
What is the first stage of a collimator?
entrance shutters (they help remove off-focus radiation)
Which set of shutters does the technologist adjust?
the second set (length and width)
How is the light field of the collimator created?
it uses a light reflected off a mirror to project coverage of the x-ray beam
How accurate does the light field need to be?
accurate within +/-2% of the SID
By law, what part of the collimator must be marked?
the Central Ray
What is something besides the Central Ray that some units project the location of?
phototimer sensors in the light field
With the collimator, what helps to center the beam with the image receptor?
an alignment light
Name two examples of Ancillary Devices:
lead blockers (shields)
lead masks (attach to collimator)
Can a PBL system filter the beam?
How would you position the wedge if you were trying to compensate for the thinness of the t-spine?
with the heel closest to the top/head
What category of filtration do collimators fall under?
What happens if you increase filtration to the amplitude of the emission spectrum?
it will go down
Will the energy ranges be narrower or wider, if you increase the overall ave energy of the beam?
What are low energy ranges typically absorbed in?
What is the most common filter material used?
What contributes to less exposure to the patient, 2 mm Al/Eq or 1 mm Al/Eq?
2 mm Al/Eq
What happens to the quality of the beam as the kVp increases?
decreases (more scatter)
What is a dedicated head unit called?
Would a diaphragm or a cone offer less penumbra?
Where is penumbra located?
the peripheral edge of the image
Is unsharpness a photographic property or a geometric property?
If the energy of the beam is decreased what would happen to the amount of attenuation?
Where is a thoreaus filter used?
(a compound filter)
How do we measure HVL (unit of measure)? to measure the radiation?