X-ray Beam Production

Question 1

What happens during excitation?
(3)

Answer 1

Energy is transferred to an orbiting electron

The electron jumps from lower to higher energy levels

The atom becomes excited

Question 2

What happens during ionisation?
(3)

Answer 2

Energy is transferred to an orbiting electron

The electron is removed from the electric field of the nucleus

The atom is ionised

Question 3

What causes heating?

Answer 3

When an electric current runs through a wire.

More current=more heat=more electrons=more interactions

Question 4

What is thermionic emission?

Answer 4

The release of electrons due to heat.

Question 5

What are the 2 processes that produce x-rays?

Answer 5

Characteristic x-rays

Bremsstrahlung

Question 6

What happens in characteristic x-rays to produce x-rays?
(6)

Answer 6

Electrons crash into the target material, hoping that they’ll hit some orbito (inner) electrons in the target material

When they collide, it causes a vacancy

The atom becomes unstable

The inner shell wants to fill the vacancy, as they only have 1 electron instead of 2

In order to replace the electron, characteristic x-rays are produced, which stabilises the atom

These x-rays use the outer electron to replace the inner electron. The change of energy causes photon x-rays

Question 7

How do auger electrons come about?

Answer 7

After the inner shell vacancy is filled by characteristic x-rays, it’s possible for an outer shell electron to be ejected instead of a photon- this emitted electron is an Auger electron

Question 8

How many times smaller is the nucleus compared to an atom?

Answer 8

The nucleus is 10 000x smaller than the atom

Question 9

What charge does the nucleus have?

Answer 9

Positive charge (+)

Question 10

What charge do electrons have?

Answer 10

Negative charge (-)

Question 11

How does Bremsstrahlung radiation produce x-rays?
(4)

Answer 11

The electron interacts with the nucleus of the target material (rather than colliding with inner electrons like in characteristic x-rays)

The electron loses (kinetic) energy and slows down

The electron changes path

The release in energy causes the release of photon energy

Question 12

What type of photon is produced during Bremsstrahlung when the electron loses lots of energy?

Answer 12

A high energy photon

Question 13

What type of photon is produced during Bremsstrahlung when the electron loses a little bit of energy?

Answer 13

A low energy photon

Question 14

When the electron collides directly with the nucleus during Bremsstrahlung, how much energy does it lose?

Answer 14

All its energy

Question 15

What is kVp?

Answer 15

The peak voltage

Question 16

What determines whether we get characteristic x-rays or not?

Answer 16

The changing energy in the x-ray tube, which changes the maximum energy of electrons

Question 17

Why are filters needed?

Answer 17

To remove low energy x-rays because they get absorbed by the patient but don’t contribute to the image. This contributes to radiation dose

Question 18

What does attenuated mean?

Answer 18

Absorbed

Question 19

What type of energy radiation is more likely to be attenuated/absorbed?

Answer 19

Low energy radiation

Question 20

When would we see a greater change in radiation?

Answer 20

When the radiation is passing through more material in the low energy part of the spectrum

Question 21

What is beam hardening?

Answer 21

When the average energy of the beam increases

Question 22

What does a change in quantity mean?

Answer 22

The distribution of energies stays the same, but the number of photons change

Question 23

How can we change the quantity?

Answer 23

By changing the mAs of the tube, e.g. running more current in the filament to cause more interactions

Question 24

What does a change in quality mean?

Answer 24

The distribution of energies changes as well as a change in the whole number of energies

Question 25

How can we change the quality?

Answer 25

By changing the kV of the tube, e.g. providing more energy to the electrons causing the x-ray production

Question 26

What does changing the quality result in?

Answer 26

A change to the shape and height of the spectra

Question 27

What does the material in an x-ray tube have to be able to do?

Answer 27

Withstand heat

Question 28

What does the filament in an x-ray tube have to be able to do?

Answer 28

Sustain/tolerate high amounts of thermionic emission

Question 29

What does the target in an x-ray tube have to be able to do? (2)

Answer 29

Dissipate heat Produce x-rays in the desired energy range

Question 30

What does the housing do in the x-ray tube?

Answer 30

It shields the undesired x-rays

Question 31

In which direction are x-rays produced in?

Answer 31

All directions

Question 32

What does the window in an x-ray tube do? (2)

Answer 32

It allows the x-rays to go in the desired direction It contributes to inherent filteration

Question 33

What is the focal point?

Answer 33

An area of the target which leads to blurring but allows better heat dissipation

Question 34

What do physical limitations of the focal point cause?

Answer 34

They cause blurring, but allows for better heat dissipation

Question 35

What is the focal point size controlled by? (2)

Answer 35

The focusing cup Filament size

Question 36

What does a small focal point do to the unsharpness?

Answer 36

It causes a smaller amount of unsharpness

Question 37

What is unsharpness?

Answer 37

A shadow

Question 38

What’s good about having a small focal point?

Answer 38

There’s a smaller amount of unsharpness (shadow), so there’s a higher resolution of the image.

Question 39

When can a small focal point be used?

Answer 39

When using small amounts of energy

Question 40

What does a larger focal point do the unsharpness?

Answer 40

There’s higher amounts of unsharpness

Question 41

Why are larger focal pints worse?

Answer 41

They cause higher amounts of unsharpness, which causes a lower resolution of the image

Question 42

When can a larger focal point be used?

Answer 42

When using big amounts of energy

Question 43

How can we minimise unsharpness? (2)

Answer 43

Put the detector close to the patient Use the smallest focal spot size you can

Question 44

What happens if the area of the target material being hit is wider? (3)

Answer 44

More electrons hit more of the target material More heat is dissipated over a larger area This causes more unsharpness

Question 45

What does a large focal spot size allow us to do to the anode?

Answer 45

It allows us to put more hat into the anode without damaging it

Question 46

What does increasing the anode angle do? (4)

Answer 46

It results in a less steep slope facing the filament It increases focal spot size, which reduces the resolution and increases the unsharpness It improves heat loading It increases the field coverage

Question 47

What does the anode heel mean?

Answer 47

It’s the idea that when x-rays are produced, electrons will be emitted at different angles. The electrons that pass through more of the target material will have less energy, and the electrons that pass through less of the target material will have more energy

Question 48

Where dos attenuation occur?

Answer 48

In the target material

Question 49

What does a longer path within the anode do to the attenuation?

Answer 49

It increases attenuation

Question 50

Where is the anode heel effect useful in radiography?

Answer 50

In mammography

Question 51

What is the anode heel impacted by?

Answer 51

The anode angle

Question 52

What does the anode heel cause?

Answer 52

It causes different intensities of photons across the x-ray field

Question 53

What minimises/eliminates the effect of the anode heel?

Answer 53

Digital corrections

Question 54

Why is the anode heel useful in mammography?

Answer 54

Because in mammography, we expect a difference in anatomy thickness across the x-ray field

Question 55

What does a larger anode angle do to the anode heel effect?

Answer 55

It reduces the anode heel’s effect

Question 56

What does the x-ray spectra depend on? (3)

Answer 56

Accelerating voltage Target material Window material

Question 57

Where is the advanced tube design used?

Answer 57

In mammography

Question 58

What does the advanced tube design say?

Answer 58

It says that the adjustment (change) of both the target material and the tube window can cause changes in very different x-ray spectra