Filtration Chapter 11 Flashcards
What is FILTRATION?
Process of eliminating unwanted low energy Xray photons by insertion of absorbing materials into the primary beam
What is the PURPOSE of filtration?
-To protect the patient by removing low energy photons that would of otherwise contribute to patient dose
Do low energy photons contribute to image quality?
No
After filtering an emission spectrum chart what is the after effect?
-Peak energy did not change
-Low energy photons removed
-Decrease in total amount of photons
-Average energy increased
-Made it harder and stronger
What is another definition for flirtation?
A process of increasing the average energy of Xray beam by taking out low energy xrays (hardening)
What is poly-energetic x ray beam?
its beam of many different energies
Why is an xray beam hetergenous?
because not all xrays are the same energies. Thats why they are Poly energetic
Why do we insert filtration into the primary beam?
To protect the patients by removing low energy photons
The number of photons is what?
the intensity or quantity
How can filtration material be expressed as?
Aluminum Equivalent (AL/Eq)
What is the standard filtering material?
Aluminum
What is Half-Value Layer?
the amount of filtration needed to reduce the beam to one half of its original intensity
What is the amount of filtration required by law with a operating range BELOW 51?
0.5mm aluminum
What is the amount of filtration required by law with a operating range of 51 to 70?
1.5mm aluminum
What is the amount of filtration required by law with a operating range ABOVE 70?
2.5mm aluminum
What are the types of filtration? (5)
Inherent
Added
Compound
Compensating
Total
What is inherent filtration?
A filtration that is the result of composition of the tube and housing
What contributes to the inherent filtration?
-thickness of the glass envelope
-dielectric oil
-the glass window of the xray tube housing
What is the typical x-ray tube total inherent filtration?
0.5-1mm AL/Eq
Why does tube aging increase inherent filtration?
because of vaporized tungsten
What is ADDED FILTRATION?
Any filtration outside of the tube and housing
NOTE
(Added filter)
Material are selected to absorb as many low energy photons as possible while transmitting maximum number of high energy photons
NOTE
(Added filter)
-Collimator averages about 1mm AL/Eq that most comes from sliver in the mirror
-1mm AL/Eq is added to exit port
What is TOTAL FILTRATION?
Its the sum of inherent and added filtration
Inherent + Added =
Total
The total does not include any
compound or compensating filters that may be added later
What is compound filtration?
Uses two or more materials in one filter that complement one another in their absorbing abilities
How are compound filter constructed?
Each layer absorbs characteristic photons created by pervious layer
A compound filter is also referred to as a
K-edge filter
Compound filters place the highest atomic number material closes to…
the tube
The lowest atomic number material is closet to the
patient
What is the final layer for compound filter?
Aluminum
The layer farthest from the patient and closest to the source is?
Copper
What is the atomic number and thickness of copper?
-29
- .25mm
What is the atomic number and thickness of aluminum?
-13
-1mm thick
What is the copper filter backed up by?
Aluminum filter
What is Compensating filter?
designed to solve a problem involving unequal subject densities
What is the reason for an compensate filter?
Compensate an unequal absorption within the subject thus making the absorption of the primary beam more equal
Compensating filter can be made of
-aluminum
-plastic
-saline solution bag
-leaded plastic trademarked under the -name ClearPb
Note
Compensate filter is also for producing a more uniform image receptor exposure
What are the two most popular compensating filter?
wedge and trough filter
What are effects on tube output?
Ideally filtration would remove low energy photons however…
Some high energy photons are removed which result in…
a decrease in radiographic exposure that must be compensated for with an increase in technique
Note
Even though the technique needs to be increased to maintain the exposure there is still a decrease in patient dose because of the removal of lower energy photons
