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Science and Technology 1 > Interactions Of X-rays With Matter > Flashcards

Interactions Of X-rays With Matter Flashcards

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1
Q

What happens to radiation as it passes through the body?

A

It undergoes different amounts of attenuation (absorption)

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2
Q

What is an x-ray image?

A

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

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3
Q

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

A

It means that more radiation has reached the detector

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4
Q

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

A

It means that no/less radiation has reached the detector

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5
Q

What are the 2 steps in primary radiation?

A

Transmission

Absorption

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6
Q

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

A

Transmission

Absorption

Scattered

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7
Q

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

A

It goes straight through the target material

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8
Q

What happens when an x-ray undergoes absorption?

A

It’s absorbed by the target material

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9
Q

What happens when an x-ray undergoes scatter?

A

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

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10
Q

What does scatter result in?

A

Blurring of the x-ray image

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11
Q

When does attenuation occur?

A

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

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12
Q

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

A

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

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13
Q

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

A

The energy of the radiation

The density of the material passing through

The type of material passing through

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14
Q

What does half value layer (HVL) mean?

A

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

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15
Q

What does the half value layer allow us to do?

A

Make comparisons with other materials

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16
Q

What is attenuation caused by?

A

Scattering

Absorption

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17
Q

What are the 2 types of scattering?

A

Elastic/coherent

Inelastic/compton

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18
Q

What are the 2 types of absorption?

A

Photoelectric effect

Pair production

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19
Q

What happens in coherent/elastic scattering?
(9)

A

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

20
Q

Does ionisation occur in coherent/elastic scattering?

A

No

21
Q

What happens in Compton/inelastic scattering?
(7)

A

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

22
Q

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

A

When we have higher energy photons

23
Q

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

A

When we have lower energy photons

24
Q

Which type of scattering happens more regularly?

A

Compton/inelastic scattering

25
Q

Where does Compton scattering occur?

A

In all tissues and bones

26
Q

What negative things does Compton scattering do?
(2)

A

It contributes to the noise of the image

It causes radiation exposure to people nearby

27
Q

What causes radiation to go in all directions?

A

Compton scattering

28
Q

Why do we have to shield from radiation?

A

Because Compton scattering causes radiation to go in all directions

29
Q

What happens in the photoelectric effect?
(8)

A

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

30
Q

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?

A

Photons must have more energy than the binding energy

31
Q

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

A

It gives us the difference in the attenuations of a patient

32
Q

What happens in pair production?
(4)

A

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

33
Q

Does pair production occur in diagnostic x-ray imaging?

A

No

34
Q

What is pair production essential for?

A

PET imaging

35
Q

Which causes of attenuation impacts image quality?
(2)

A

Inelastic/compton (scattering)

Photoelectric effect (absorption)

36
Q

How does Compton scattering differ for all materials?

A

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

37
Q

Different attenuation results in … differences

A

In contrast differences

38
Q

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

A

Lead- small amounts are highly attenuating and can be used for radiation safety purposes

Contrast- it enhances attenuation to highlight something in an image

39
Q

What are contrast agent?

A

Substances that increase the contrast of structures in the body

40
Q

What does the introduction of contrast increase?
(2)

A

It increases attenuation

It increases the contrast

41
Q

When is the Compton effect more likely?
(2)

A

At lower atomic numbers

At higher energies

42
Q

What does intensity mean?

A

The amount of radiation passing through an area

43
Q

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

A

Linear attenuation coefficient

Thickness of the material

44
Q

What is the binding energy?

A

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

45
Q

What is the K edge?

A

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

46
Q

What is a positron?

A

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

Science and Technology 1 (17 decks)

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