Filtration

Question 1

What is the function of filtration within an x-ray tube?

Answer 1

Filters out low energy photons

Question 2

What are examples of filtration in a tube?

Answer 2

• Sheet of Aluminum or Copper
• Inherent filtration (collimator mirror, x-ray tube window)

Question 3

What is the aluminum equivalent of filtration?

Answer 3

2.5 mm Al/equivalent

Question 4

What is the 2.5 mm AL/equivalent made up of?

Answer 4

The inherent filtration + added filtration

Question 5

What is filtration designed to do in regards to dose?

Answer 5

Reduce patient exposure to photons of long wavelengths (low energy photons)

Question 6

What happens to the average beam energy after filtration?

Answer 6

The average beam energy will go up but the overall intensity goes down

Question 7

If too much filtration were to be added what is the effect on the resulting image?

Answer 7

Have noise

Question 8

What affect does filtration have on the image?

Answer 8

None, it doesn’t make the image better or change spatial resolution

Question 9

How does filtration harden the beam?

Answer 9

By removing weaker photons and making a stronger beam

Question 10

What happens to the intensity (quantity) of the beam after filtration?

Answer 10

Overall intensity does down because the low energy photons are removed

Question 11

What are the two types of filtration?

Answer 11

Inherent and added

Question 12

What is inherent filtration?

Answer 12

Consists of components of the x-ray tube and housing that remove the low energy photons

Question 13

What are specific examples of inherent filtration?

Answer 13

Glass in the tube, parts of the collimator, oil and the beryllium window

Question 14

What is added filtration?

Answer 14

Consists of sheets of aluminum that are placed between the tube and the collimator

Question 15

What is the minimum filtrations needed for x-ray tubes that operate over 70 kVp?

Answer 15

2.5 mm Al/equivalent

Question 16

What is the total amount of inherent filtration in an x-ray tube?

Answer 16

1.5 mm Al/equivalent

Question 17

What is a half value layer?

Answer 17

The amount of filtration required to reduce the radiation intensity by one half the original amount

Question 18

What are HVL’s based on?

Answer 18

Generator type and manufacturer, which means there is not set HVL for all machines

Question 19

What part of the beam are filters reducing the intensity in?

Answer 19

The primary beam only, not the remnant beam

Question 20

What are compensating filters?

Answer 20

Filters that are used with body parts that have a rapid change in tissue mass, and are intended to even out the intensity at the IR

Question 21

What body parts typically require compensating filters?

Answer 21

Feet

Question 22

How do compensating filters work?

Answer 22

They allow more radiation on the thicker areas of the part and less where the part is thin

Question 23

What is a common compensating filter used for feet?

Answer 23

Wedge filter

Question 24

What can be used instead of a physical compensation filter?

Answer 24

Computer algorithm in post production

Question 25

What series are some of the only exposures that still use physical filters?

Answer 25

Scoliosis series