Filtration

Question 1

What is filtration in radiology?

Answer 1

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.

Question 2

What are the two definitions of filtration?

Answer 2

• 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.

Question 3

What is the purpose of filtration?

Answer 3

To protect the patient by removing low energy photons that would otherwise contribute to patient dose.

Question 4

What happens to the average energy of the x-ray beam after filtration?

Answer 4

The average energy increases as low energy photons are removed.

Question 5

True or False: The peak energy of the x-ray beam changes after filtration.

Answer 5

False

Question 6

What is meant by ‘hardening’ in the context of x-ray beams?

Answer 6

The process of increasing the average energy of the x-ray beam by removing low energy x-rays.

Question 7

What is the intensity of a beam with 6 photons?

Answer 7

6

Question 8

What is the formula to calculate average energy of the x-ray beam?

Answer 8

Total energy of photons / Number of photons

Question 9

What is the average energy of a beam with 6 photons: 100 kV, 30 kV, 75 kV, 80 kV, 90 kV, and 80 kV?

Answer 9

75.8 kV

Question 10

What happens to low energy photons during filtration?

Answer 10

They are filtered out or absorbed by the filter material.

Question 11

What is the aluminum equivalent (Al/Eq) in filtration?

Answer 11

A standard measure for expressing filtration material in terms of its ability to filter x-rays.

Question 12

What does the term ‘Half-Value Layer (HVL)’ refer to?

Answer 12

The amount of filtration needed to reduce the beam to one half of its original intensity.

Question 13

What are the types of filtration?

Answer 13

• Inherent filtration
• Added filtration
• Compound filtration
• Compensating filtration
• Total filtration

Question 14

What is inherent filtration?

Answer 14

Filtration that is a result of the composition of the tube and housing.

Question 15

What is the typical range of inherent filtration in x-ray tubes?

Answer 15

0.5–1 mm Al/Eq

Question 16

What is added filtration?

Answer 16

Any filtration outside of the tube and housing designed to absorb low energy photons while transmitting high energy photons.

Question 17

What is the sum of inherent and added filtration known as?

Answer 17

Total filtration

Question 18

What is compound filtration?

Answer 18

Filtration that uses two or more materials in one filter that complement one another in their absorbing abilities.

Question 19

What is a common material used in compound filtration?

Answer 19

Copper

Question 20

What is compensating filtration designed to address?

Answer 20

Unequal subject densities to produce a more uniform image receptor exposure.

Question 21

Name two popular types of compensating filters.

Answer 21

• Wedge filter
• Trough filter

Question 22

What effect does filtration have on tube output?

Answer 22

It removes some high energy photons, resulting in a decrease in radiographic exposure.

Question 23

What must be done to maintain exposure after filtration?

Answer 23

Increase in technique.

Question 24

True or False: Increasing technique after filtration results in an increase in patient dose.

Answer 24

False