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Radiation Protection > Week 3 - Interactions > Flashcards

Week 3 - Interactions Flashcards

1
Q

Why are the processes of interaction between radiation and matter important?

A

Because a basic understanding is necessary to set technical exposure factors when imaging

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2
Q

What are the important technical exposure factors worth knowing?

A

kVp (peak kilovoltage) and mAs (milliampere-seconds)

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3
Q

What is kVp?

A

Highest energy level photons in the x-ray beam equal to highest voltage established across the tube

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4
Q

What does kVp control?

A

Quality/penetrating power of the photons in the beam and to some degree the quantity of photons

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5
Q

What is mAs?

A

The product of milliampere and the amount of time in seconds the tube is activated

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6
Q

What is mA?

A

The current of the electron tube

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7
Q

What is the formula for mAs?

A

mA x s = mAs

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8
Q

What does mAs control?

A

The Quantity of radiation that is directed toward the patient during exposure

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9
Q

What is the radiographer responsible for when imaging?

A
  • Setting the technical exposure factor that control quality/quality of the beam
  • Selecting the dose the patient receives
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10
Q

What can selecting appropriate techniques achieve with imaging?

A
  • Minimized dose to patients
  • Images of optimal-quality
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11
Q

What do x-ray carry?

A

Manmade electromagnetic energy

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12
Q

What are the 3 ways x-rays enter a material such as human tissues?

A
  • Interact with atoms of the tissue and are absorbed
  • Interact with atoms of the tissue and are scattered, causing indirect transmission
  • Pass through without interaction
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13
Q

What is absorption?

A

When electromagnetic energy is transferred from the x-rays to the atoms of a patient’s tissue

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14
Q

What is absorbed dose?

A

The amount of energy per unit mass

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15
Q

How can biologic damage be minimized?

A

By keeping the amount of electromagnetic energy transferred to patient as small as possible

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16
Q

Why is absorption important to diagnostically useful images?

A

Helps distinguish anatomic structures in images

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17
Q

What are the benefits to keeping patient dose minimal?

A
  • Less radiation is scattered from the patient
  • Reduces occupational hazards to the radiographer
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18
Q

How is a diagnostic x-ray beam produced?

A

When a stream of high-speed electrons bombard a positively charged target in a evacuated glass tube

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19
Q

What are anodes composed of?

A

Tungsten (metal) or Tungsten rhenium (metal alloy)

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20
Q

Why are tungsten and tungsten rhenium used as target materials?

A
  • Have high melting points
  • High atomic numbers
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21
Q

Do all photons in an x-ray beam have the same energy?

A

No, they have variable energy levels

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22
Q

What is the max energy a photon can have?

A

No more energy that the electrons that bombard the target

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23
Q

What is the energy of the electrons inside the tube specified in?

A

In terms of electrical voltage applied across the tube

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24
Q

In diagnostic radiology, what is the energy of electrons in the tube is expressed in?

A

kV, but because the voltage fluctuates its usually expressed in kVp

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25
Q

What is attenuation?

A

When an x-ray beam passes through a patient

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26
Q

What is direct transmission?

A

When primary photons traverse the patient without interacting and hit the image receptor

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27
Q

What is indirect transmission?

A

When primary photons traverse the patient with interacting and hit the image receptor

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28
Q

What is attenuation?

A

The reduction in intensity of the x-ray beam after its passed through a patient

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29
Q

What two mechanisms produce attenuation?

A

Absorption and Scattering

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30
Q

What is scattering?

A

A change in direction of a photon after interaction with an atom

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31
Q

What is small- angle scatter?

A

When the beam changes direction only slightly so that its still directed towards the IR

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32
Q

How does small-angle scatter interfere with image production?

A

It produces radiation fog

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33
Q

When is an optimal x-ray image formed?

A

When only direct transmission x-rays photons reach the IR

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34
Q

What methods can be used to limit the effects of indirect transmission photons?

A

Radiographic grids and air gap techniques

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35
Q

What types of transmission form radiographic images?

A

Direct and Indirect transmitted x-ray photons

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36
Q

What problems are caused by radiographic fog?

A

Interferes with the radiologists ability to distinguish different structures in the image

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37
Q

How can radiographic fog be reduced?

A

By reducing the amount of tissue irradiated, which is done via collimation

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38
Q

How can the probability of photon interactions with biologic matter be described?

A

Random

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39
Q

What can be predicted when photons enter tissue?

A

What will happen on average when a large number of photons enter the body

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40
Q

What does predicting photon interactions determine?

A

The characteristics of the image that results from these types of interactions

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41
Q

When primary radiation emerges from the x-ray tube what properties do the photons have?

A

X-ray photons of various energies

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42
Q

What are primary photons?

A

Photons that emerge from the x-ray source before they hit the body

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43
Q

What are exit, or image-formation, photons?

A

Photons that pass through the patient being radiographed and reach the image receptor

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44
Q

What are attenuated photons?

A

Photons that have interacted with the patient and have been scattered so that they don’t reach the IR

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45
Q

What does the probability of a photon interacting with tissue dependent on?

A

Dependent on photon energy and the characteristics of the tissue

46
Q

What are the 5 possible interactions of photons with matter?

A
  • Coherent scattering
  • Photoelectric absorption
  • Compton scattering
  • Pair production
  • Photodisintegration
47
Q

Which of the two interactions are important for the energies used in diagnostic x-ray?

A

Compton scattering and Photoelectric absorption

48
Q

What diagnostic kV range do Compton and Photoelectric interactions?

A

50-150 kV

49
Q

When is Compton scattering more likely?

A

When using higher Kv

50
Q

When is Photoelectric absorption more likely?

A

When using lower Kv

51
Q

What is Coherent scatter also known as?

A

Classical, elastic, unmodified or Rayleigh scattering

52
Q

What type of energy loss results from Coherent scattering?

A

No loss of energy as x-rays scatter

53
Q

What type of energy does Coherent scattering occur in?

A

Low energy photons less than 10 kEv

54
Q

What is the net result of Coherent scattering?

A

A change in direction of less than 20 degrees from the incident photon

55
Q

What is the process of coherent scattering?

A

The incoming low-energy photon interacts with an atom and transfers its energies causing the electrons to vibrate. When the electrons vibrate they release energy in the form of electromagnetic waves which nondestructively combine to form a scattered wave.

56
Q

What type of interaction does Coherent scattering produce?

A

Excitation

57
Q

What photon energy range does Coherent scattering occur in?

A

1-50 kVp

58
Q

What is the site of interaction for Coherent scattering?

A

The atom

59
Q

What is the by-product of Coherent scattering?

A

Nothing

60
Q

What does the probability of Coherent scattering depend on?

A

Photon energy and mass density

61
Q

How is probability of Coherent scattering related to photon energy?

A

As photon energy increase probability of Coherent scattering decreases

62
Q

How is probability of Coherent scattering related to mass density?

A

As mass density increases the probability of Coherent scattering increases

63
Q

What is the most important mode of interaction between x-ray photons and atoms?

A

Photoelectric Absorption

64
Q

What does absorption depend strongly on?

A

The type of tissue, characterized by the atomic number

65
Q

What is used with the atomic differences between tissues are not great enough?

A

Contrast media

66
Q

What is the process of photoelectric absorption?

A
  • X-ray photon encounters an inner-shell electron and surrenders all its energy to the electron, and the photon ceases to exist
  • The atom ejects the electron, which is now called a photoelectron, and creates a vacancy
  • The opening is then filled with an electron dropping down from an outer shell releasing energy in the form of a characteristic photon. (occurs until atom electron equilibrium is reached)
67
Q

What is another probability that occurs in photoelectric absorption?

A

An auger electron is ejected

68
Q

What is the Auger effect?

A

A radiationless effect that occurs as a result of photoelectric absorption

69
Q

What is the process of the Auger Effect?

A
  • Characteristic energy, that is released when an inner shell vacancy is filled, is transferred to another electron in an outer shell and ejects it
70
Q

What is the liberated electron called?

A

Auger electron

71
Q

What type of interaction does photoelectric absorption produce?

A

Absorption

72
Q

What photon energy range does Photoelectric absorption occur in?

A

Low to moderate 1-50 kVp

73
Q

What is the site of interaction of Photoelectric Absorption?

A

Inner orbital electron, usually K or L shell

74
Q

What is the by-product of interaction of photoelectric absorption?

A
  • Photoelectron
  • 1 of more characteristic photons
75
Q

What does the probability of Photoelectric absorption depend on?

A

Photon Energy, Atomic number and Mass density

76
Q

How is probability of Photoelectric Absorption related to photon energy?

A

Inversely proportional to keV^3
The higher energy photons are less likely to be absorbed

77
Q

How is probability of Photoelectric Scattering related to atomic number of tissue?

A

Proportional to Z^3

78
Q

How is probability of Photoelectric Absorption related to mass density?

A

Proportional to mass density

79
Q

What color does positive contrast medium reflect in x-ray images?

A

White

80
Q

What color does negative contrast medium reflect in x-ray images?

A

Black

81
Q

What is the impact of photoelectric absorption on contrast?

A

The greater the different in the amount of absorption, the greater the contrast in the image

82
Q

What is Compton scattering also known as?

A

Incoherent, inelastic and modified scattering

83
Q

Why is compton scattering important to radiography?

A

When photons change direction, they can exit the patient at a different direction that initiated and produce scatter fog which reduces image quality

84
Q

What is the process of compton scattering?

A
  • A photon interacts with an outer shell electron and is deflected with loss of energy
  • Some of the photons energy is transferred to the electron (amount of energy transfers increases with the angle of scatter)
85
Q

When does compton scatter occur?

A

When the x-ray photon energy is very high compared to electron binding energy

86
Q

What type of interaction does compton scattering produce?

A

Ionization

87
Q

What photon energy range does Compton scattering occur in?

A

Moderate to high 50-150 kVp

88
Q

What is the site of interaction of compton scattering?

A

Outer orbital electron

89
Q

What is the by-product of interaction of compton scattering?

A
  • Compton scattered electron, secondary/recoil electron
  • Compton scattered proton with low energy
90
Q

What does the probability of compton scattering depend on?

A
  • Photon energy
  • Mass energy
91
Q

How is probability of compton scattering related to photon energy?

A

Probability increases with increasing energy

92
Q

How is probability of Compton scattering related to mass density?

A

Probability increase with mass density increase

93
Q

What is the process of pair production?

A
  • A photon with energy > 1.02 MeV interacts with the nuclear field of an atom
  • It transfers all its energy to the atom to produce an electron-positron pair
  • As a result, the unstable positron combines with an electron to produce annihilation radiation
94
Q

What type of interaction does pair production produce?

A

Energy to matter transformation

95
Q

What photon energy range does pair production occur in?

A

Greater that 1.022 Mev

96
Q

What is the site of interaction of pair production?

A

A nuclear electric field

97
Q

What is the by- product of interaction of pair production?

A

A negatron and positron, which splits into two 0.511 meV photons

98
Q

What does the probability of pair production depend on?

A
  • Photon energy
  • Atomic # of absorber
  • Mass density
99
Q

How is probability of Pair production related to photon energy?

A

Probability increase with increase in energy

100
Q

How is probability of Pair production related to Mass density?

A

Proportional to mass density

101
Q

How is probability of pair production related to atom number?

A

Probability increases with atomic number

102
Q

What are the uses of annihilation radiation in PET?

A
  • sources of positrons
  • process of positron decay
  • formation of annihilation photons
103
Q

What is photodisintegration interaction?

A

An interaction that occurs at more the 10 MeV high energy radiation in radiation therapy machines

104
Q

What effect does photodisintegration have on the nucleus of an atom?

A

Causes the nucleus of an atom to change in some way or break apart

105
Q

Why type of interaction does photodisintegration produce?

A

Nuclear disintegration

106
Q

What photon energy range does Photodisintegration occur in?

A

Very high photon range >10 MeV

107
Q

Where is the site of interaction of photodisintegration?

A

Nucleus

108
Q

What is the by-product of photodisintegration?

A

Nuclear fragments

109
Q

What does the probability of photodisintegration depend on?

A
  • Photon energy
  • Atomic number of absorber
  • Mass density
110
Q

H

A

Radiation Protection (15 decks)

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