Filtration Flashcards
What is filtration in radiology?
The process of eliminating undesirable low-energy x-ray photons by the insertion of absorbing materials into the primary beam.
Filtration protects the patient by removing low energy photons that would otherwise contribute to patient dose.
What are the two definitions of filtration?
- The process of eliminating undesirable low-energy x-ray photons by the insertion of absorbing materials into the primary beam
- A process of increasing the average energy of the x-ray beam by taking out low energy x-rays.
What is the purpose of filtration?
To protect the patient by removing low energy photons that would otherwise contribute to patient dose.
What happens to the average energy of the x-ray beam after filtration?
The average energy increases as low energy photons are removed.
True or False: The peak energy of the x-ray beam changes after filtration.
False
What is meant by ‘hardening’ in the context of x-ray beams?
The process of increasing the average energy of the x-ray beam by removing low energy x-rays.
What is the intensity of a beam with 6 photons?
6
What is the formula to calculate average energy of the x-ray beam?
Total energy of photons / Number of photons
What is the average energy of a beam with 6 photons: 100 kV, 30 kV, 75 kV, 80 kV, 90 kV, and 80 kV?
75.8 kV
What happens to low energy photons during filtration?
They are filtered out or absorbed by the filter material.
What is the aluminum equivalent (Al/Eq) in filtration?
A standard measure for expressing filtration material in terms of its ability to filter x-rays.
What does the term ‘Half-Value Layer (HVL)’ refer to?
The amount of filtration needed to reduce the beam to one half of its original intensity.
What are the types of filtration?
- Inherent filtration
- Added filtration
- Compound filtration
- Compensating filtration
- Total filtration
What is inherent filtration?
Filtration that is a result of the composition of the tube and housing.
What is the typical range of inherent filtration in x-ray tubes?
0.5–1 mm Al/Eq
What is added filtration?
Any filtration outside of the tube and housing designed to absorb low energy photons while transmitting high energy photons.
What is the sum of inherent and added filtration known as?
Total filtration
What is compound filtration?
Filtration that uses two or more materials in one filter that complement one another in their absorbing abilities.
What is a common material used in compound filtration?
Copper
What is compensating filtration designed to address?
Unequal subject densities to produce a more uniform image receptor exposure.
Name two popular types of compensating filters.
- Wedge filter
- Trough filter
What effect does filtration have on tube output?
It removes some high energy photons, resulting in a decrease in radiographic exposure.
What must be done to maintain exposure after filtration?
Increase in technique.
True or False: Increasing technique after filtration results in an increase in patient dose.
False
