Interactions Of X-rays With Matter

Question 1

What happens to radiation as it passes through the body?

Answer 1

It undergoes different amounts of attenuation (absorption)

Question 2

What is an x-ray image?

Answer 2

A visual display in the difference of x-ray attenuation at different positions

Question 3

What does it mean if an x-ray image is black?

Answer 3

It means that more radiation has reached the detector

Question 4

What does it mean if an x-ray image is white?

Answer 4

It means that no/less radiation has reached the detector

Question 5

What are the 2 steps in primary radiation?

Answer 5

Transmission

Absorption

Question 6

What will all x-ray either be?
(3)

Answer 6

Transmission

Absorption

Scattered

Question 7

What does is mean if an x-ray undergoes transmission?

Answer 7

It goes straight through the target material

Question 8

What happens when an x-ray undergoes absorption?

Answer 8

It’s absorbed by the target material

Question 9

What happens when an x-ray undergoes scatter?

Answer 9

The radiation either goes straight through the patient or reaches another point in the detector

Question 10

What does scatter result in?

Answer 10

Blurring of the x-ray image

Question 11

When does attenuation occur?

Answer 11

When there’s a sharp decrease in the intensity of the radiation, which slows down as the thickness of the material increases

Question 12

Why does the intensity of the radiation decrease as the thickness of the material increases?

Answer 12

Because the radiation is coming into contact with more of the material

Question 13

What does the linear attenuation coefficient depend on?
(3)

Answer 13

The energy of the radiation

The density of the material passing through

The type of material passing through

Question 14

What does half value layer (HVL) mean?

Answer 14

For a given material, certain energy is needed to get half of the intensity that we started with

Question 15

What does the half value layer allow us to do?

Answer 15

Make comparisons with other materials

Question 16

What is attenuation caused by?

Answer 16

Scattering

Absorption

Question 17

What are the 2 types of scattering?

Answer 17

Elastic/coherent

Inelastic/compton

Question 18

What are the 2 types of absorption?

Answer 18

Photoelectric effect

Pair production

Question 19

What happens in coherent/elastic scattering?
(9)

Answer 19

The incident electron interacts with the target material

This gives energy to the atom

The photon is absorbed

The atom gains energy and becomes excited

The atom wants to get rid of the additional energy

In order to do this, it releases the photon in another direction than it entered

Most photons are absorbed by the patient

The patient receives radiation

The atom becomes stable

Question 20

Does ionisation occur in coherent/elastic scattering?

Answer 20

No

Question 21

What happens in Compton/inelastic scattering?
(7)

Answer 21

The photon enters the atom

The photon interacts with an electron

Some of the electrons scatter the photons

The photons are released in another direction

This gives energy to the electron

The atom becomes ionisied

The electron becomes a free electron

Question 22

When are we less likely to see Compton/inelastic scattering?

Answer 22

When we have higher energy photons

Question 23

When are we more likely to see Compton/inelastic scattering?

Answer 23

When we have lower energy photons

Question 24

Which type of scattering happens more regularly?

Answer 24

Compton/inelastic scattering

Question 25

Where does Compton scattering occur?

Answer 25

In all tissues and bones

Question 26

What negative things does Compton scattering do? (2)

Answer 26

It contributes to the noise of the image It causes radiation exposure to people nearby

Question 27

What causes radiation to go in all directions?

Answer 27

Compton scattering

Question 28

Why do we have to shield from radiation?

Answer 28

Because Compton scattering causes radiation to go in all directions

Question 29

What happens in the photoelectric effect? (8)

Answer 29

Photons enter the atom Energy is given to electrons Electrons get ionised Electrons leave the atom This causes a vacancy The vacancy can be filled by another electron This causes multiple characteristic x-rays This increases the radiation dose to the patient IF we have the energy to overcome the binding energy

Question 30

In order for the photoelectric effect to produce characteristic x-rays and increase the radiation dose, do photons have to have more or less energy than the binding energy?

Answer 30

Photons must have more energy than the binding energy

Question 31

What does the photoelectric effect allow for the attenuation of the patient?

Answer 31

It gives us the difference in the attenuations of a patient

Question 32

What happens in pair production? (4)

Answer 32

The photon interacts directly with the nucleus This causes an electron-positron pair to be created near the nucleus The positron later gets annihilated by another electron This creates two 511 keV photons IF the x-rays are above 1.02 MeV The photons go in opposite directions

Question 33

Does pair production occur in diagnostic x-ray imaging?

Answer 33

No

Question 34

What is pair production essential for?

Answer 34

PET imaging

Question 35

Which causes of attenuation impacts image quality? (2)

Answer 35

Inelastic/compton (scattering) Photoelectric effect (absorption)

Question 36

How does Compton scattering differ for all materials?

Answer 36

It doesn’t- it’s similar for all materials

Question 37

Different attenuation results in … differences

Answer 37

In contrast differences

Question 38

What are the uses of highly attenuating materials? (2)

Answer 38

Lead- small amounts are highly attenuating and can be used for radiation safety purposes Contrast- it enhances attenuation to highlight something in an image

Question 39

What are contrast agent?

Answer 39

Substances that increase the contrast of structures in the body

Question 40

What does the introduction of contrast increase? (2)

Answer 40

It increases attenuation It increases the contrast

Question 41

When is the Compton effect more likely? (2)

Answer 41

At lower atomic numbers At higher energies

Question 42

What does intensity mean?

Answer 42

The amount of radiation passing through an area

Question 43

What are the key properties of x-ray attenuation? (2)

Answer 43

Linear attenuation coefficient Thickness of the material

Question 44

What is the binding energy?

Answer 44

The energy that every electron has to hold them in place in the shell

Question 45

What is the K edge?

Answer 45

The sudden increase in energy when the photon energy exceeds a binding shell threshold

Question 46

What is a positron?

Answer 46

A positively charged subatomic particle that has the same mass and charge as an electron