Beam parameters, filtration, xray interactions

Question 1

What imapct does modifying tube current have on the energy spectrum?

Answer 1

Impacts the amplitude

Question 2

Impact of modifying tube voltage on energy spectrum.

Answer 2

Impacts amplitude and position

Question 3

Impact of modifying filtration on energy spectrum

Answer 3

impacts amplitude and shows most impact on lower energies.

Question 4

Impact of modifying target material on energy spectrum

Answer 4

Amplitude and position of line (characteristic peak)

Question 5

Impact of modifying voltage waveform on energy spectrum

Answer 5

Amplitude and shows most impact for higher energies.

Question 6

Why is modifying the beam important?

Answer 6

It ensures that the overall patient dose is reduced and also overall dose for the other radiographers is also reduced.

Question 7

What parameters increase x-ray quantity?

Answer 7

increasing mAs, kVp

Question 8

What parameters decrease x-ray quantity?

Answer 8

increasing distance and filtration

Question 9

How is x-ray quality defined?

Answer 9

As the penetrability of the beam.

Question 10

How is x-ray quality measured?

Answer 10

HVL

Question 11

What is half value layer?

Answer 11

the thickness of a material at which the intensity of radiation is reduced by a half.

Question 12

How is the half value layer increased?

Answer 12

increasing kilovolt peak (kVp) = increasing quality of beam = increasing HVL

Question 13

What is filtration?

Answer 13

The process of filtration is to remove low energy x-rays (by absorbing them) so the consequent beam is of high energy.

Question 14

What one factor increases both quality AND quantity of a beam and how?

Answer 14

Tube voltage.
By changing the tube voltage, the potential difference between the anode and cathode is modified. As the electrons are accelerated, more x-rays reach the detector (increasing quantity) as well as there is an increase in overall beam energy (quality).

Question 15

State the inverse square law

Answer 15

Intensity = 1/ distance^2

Question 16

What are the 3 things that can happen when x-ray beams come into contact with a material?

Answer 16

They can be either absorbed, scattered or transversed w/o any interaction.

Question 17

What does attentuation mean?

Answer 17

Attenuation refers to the x-rays that are absorbed and scattered.

Question 18

Define mono and poly energetic energies.

Answer 18

Mono - a type of energy which which is fixed and does not change with attenuation at any depth. A hVL can be calculated for this type of energy.

Poly - Consist of both low and high energies. Low energy rays are absorbed faster and the high energy xrays are more penetrating. The hvl for this also keeps chagnging.
These are the beams we see in real life.

Question 19

Why is filtration important?

Answer 19

1. As lower energies are absorbed, the overall beam energy increases.
2. The absorption of lower energy x-rays that dont add to the image, ensures that they are not absorbed by tissues (thus adding to patient dose).

Question 20

What are the 2 types of filtration?

Answer 20

Inherent and added filtration

Question 21

What is inherent filtration? What material does it use and at what thickness?

Answer 21

includes the windows of x-ray tubes and other enclosures of the tube itself.
The filter used is 0.5 mm of aluminium.

Question 22

What is added filtration? What material does it use and at what thickness?

Answer 22

includes a thin layer of Al between the x-ray tube and the beam collimator.
The filter uses I mm of Al to filter the collimator.

Question 23

Why is Al a good choice of filter?

Answer 23

1. removes x-rays beams w/o decreasing beam intensity
2. Lightweight and sturdy
3. inexpensive

Question 24

An alternative to Al for filter material?

Answer 24

copper

Question 25

What is a compensating filter? Give an example.

Answer 25

it is a filter used when producing an image with non-uniform intensity (with varying thickness and tissue composition).
For e.g. a block filter is used when takingan x-ray of the foot (which is non-uniform).