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1613: Physics > Unit Two > Flashcards

Unit Two Flashcards

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1
Q

Attenuation

A

Removal of any photons from the primary beam before striking the IR.

A reduction in x-ray beam intensity as it passes through matter

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2
Q

What causes attenuation

A

1) Pt. absorption (DA)
2) Compton scatter that doesn’t strike IR.

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3
Q

Differential Absorption

A

the difference between the xray photons that are absorbed and those that penetrate the body

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4
Q

Why is it called DA?

A

different body structures absorb xray photons to different extents

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5
Q

Differential Attenuation

A

a form of primary beam attenuation specific to pt. absorption and transmission.

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6
Q

Absorption

A

refers to xray photons that are attenuated by the body and don’t reach the IR

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7
Q

Transmission

A

refers to xray photons that pass through the body and reach the IR

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8
Q

Primary Beam

A

the xray beam as it is upon exiting the collimator and exposing the pt

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9
Q

Remnant Beam

A

the xray beam that remains after interaction with the pt. and that is exiting the pt to expose the IR

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10
Q

What is the remnant beam composed of?

A

Transmitted photons and scattered photons

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11
Q

Radiopaque

A

body structures that readily absorb xray photons (bones)

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12
Q

Radiolucent

A

less dense body structures that have a much lower probability of absorption (air-filled lungs)

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13
Q

Factors that affect Radiographic Contrast

A
  1. kVp
  2. Differential absorption
  3. computer processing and display
  4. filtration
  5. compton scatter
  6. radiographic grids
  7. OID
  8. beam restriction
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14
Q

Increased levels of DA = _____ b/w on radiograph

A

Increased

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15
Q

Radiograph with increased DA = _____ subject contrast = _____ gray scale

A

High
Short

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16
Q

Decreased DA = ____ gray on radiograph

A

more

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17
Q

Radiograph with decreased DA = ____ subject contrast = _____ gray scale

A

low
long

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18
Q

a uniform exposure on the IR that causes a loss of visible image contrast

A

noise

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19
Q

What causes noise

A

Compton Scatter

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20
Q

Most common beam restriction?

A

Collimation

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21
Q

Increased field size = ____ scattered xrays (scattered radiation)

A

increased

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22
Q

5 types of interaction with matter

A
  1. coherent (classical) scatter
  2. compton scatter
  3. photoelectric effect
  4. pair production
  5. photodisintigration
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23
Q

Other names for coherent scatter

A

Classical
Thompson

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24
Q

Coherent scatter energy

A

less than 10 kev

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25
Q

Coherent scatter steps

A
  1. X-ray with energy less than 10 kev interacts with a target atom = atom excited
  2. target atom releases energy as a scattered photon w/ a wavelength = to the incident xray
  3. Result = change of direction of xray w/out a change in energy
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26
Q

Scatter with no ionization and no energy transfer

A

coherent scatter

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27
Q

Coherent scatter’s contribution to medical image

A

very little

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28
Q

At ___ kVp, a small % of xrays undergo coherent scattering

A

70

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29
Q

Xrays undergoing an interaction w/ an outershell electron that change direction, reduces photon energy, and ionizes the atom.

A

Compton scatter

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30
Q

Compton scatter steps

A
  1. incident xray interacts w/ outershell electron and ejects it from the atom = ionization
  2. xray photon contributes to different direction w/ a reduction in energy
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31
Q

Name of electron ejected during a compton (outershell) scatter reaction

A

Recoil electron
Compton electron

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32
Q

Energy of comton scattered xray

A

Energy of incident xray - energy of ejected electron

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33
Q

Energy of ejected electron

A

binding energy + kinetic energy

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34
Q

during compton scattering, most energy is divided between ______ and _____

A

scattered xray and compton electron

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35
Q

During compton scattering, the scattered xray retains ____ of energy

A

most of

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36
Q

The amount of energy that ionizing radiation imparts to a given mass of matter.

The amount of radiation absorbed by an object

A

Dose or Absorbed Dose

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37
Q

Compton scatter contributes to

A
  1. Decreased image contrast
  2. Pt dose
  3. Occupational dose
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38
Q

3 types of compton scatter

A

1) Back scatter
2) Side scatter
3) Forward scatter

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39
Q

Back scatter

A

photon scatters 180 degrees perpendicular to the primary beam, strikes the IR, and travels back in direction of the incident xray beam

  • can contribute to pt dose
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40
Q

Type of scatter when the photon strikes the outershell electron head-on

A

Back scatter

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41
Q

Type of scatter when the photon strikes the outershell electron on the outer edge

A

Side scatter

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42
Q

Main source of occupational dose (specifically in Fluro)

A

Side scatter

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43
Q

Type of scatter when the photon grazes the orbital electron, barely gives up its energy, and travels forward to strike the IR

A

Forward scatter

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44
Q

Increased xray energies increased probability of _____ scatter

A

forward

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45
Q

Factors affecting production of compton scatter

A
  1. field size (collimation)
  2. body part thickness
  3. body part density
  4. body part electron density
  5. photon energy
  6. kVp
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46
Q

Increased field size = ____ intensity of scattered xrays

A

increased

47
Q

Increased field size = _____ noise = _____ in overall image contrast

A

Increased
Decreased

48
Q

Decreased field size = ____ compton scatter production in pt.

A

Decreased

49
Q

Most effective way of decreasing dose

A

Decreasing field size (collimation)

50
Q

Thicker part = ____ compton scatter than thinner part

A

More

51
Q

Compression Results in:

A

Thinner part
Reduction in Compton scatter
Increased image contrast

52
Q

Increased part density = ____ production of compton scatter

A

Increased

53
Q

Why does a body part with a large volume of matter produce more scattered xrays?

A

Due to increased presence of hydrogen atoms and water rich tissues being more electron dense

54
Q

Does atomic number of a tissue affect the likelihood of compton scatter?

A

NO

55
Q

An ____ in the presence of water in soft tissue makes it to where compton is more likely

A

Increase

56
Q

Hydrogen atom composition

A

No neutrons
Nucleus only has one proton and one electron

57
Q

_____ amount of water present in a type of tissue = _____ amount of compton

A

Increase

57
Q
A
57
Q

Hydrogen atoms have _____ the amount (density) of electrons per cubit cm.

A

2x

58
Q

As kVp increases, the likelihood of compton decreases because

A

Transmission increases as kVp increases

59
Q

An increase in kVp makes a larger beam, which leads to more compton events but, _____- average compton events

A

decreased

60
Q

Ways to reduce compton scatter

A
  1. Lowest possible kVp
  2. Grids
  3. Collimation
  4. Air gap technique
  5. Part compression
61
Q

Photoelectric effect =

A

Absorption
(photoelectric absorption)

62
Q

Photoelectric effect happens when

A

xrays have ionizing interactions with inner-shell electrons

63
Q

In photoelectric effect, the xrays are not scattered, but

A

totally absorbed

64
Q

An electron removed from an atom during photoelectron effect is called

A

Photoelectron

65
Q

Photoelectron kinetic energy

A

energy of the incident xray - the binding enrgy of electron

66
Q

Photoelectric Effect:

The incident photon is absorbed by what shell?

A

K

67
Q

Photoelectric Effect steps

A
  1. Incident xray is absorbed by inner (K) electron
  2. K-shell electron enters an excited state and is ejected from the shell.
  3. Photoelectric effect produces secondary radiation through the cascading effect.
68
Q

A photoelectric interaction cannot occur unless

A

The incident xray has energy equal to or slightly greater than the electron binding energy

69
Q

Barium K-shell binding energy

A

37kev

70
Q

Factors affecting Photoelectric Effect

A
  1. kVp
  2. Body part thickness
  3. Body part density
  4. Atomoic number of tissue
71
Q

Photoelectric Effect relation with kVp

A

Indirect
(kVp up = PE down)

72
Q

Photoelectric Effect relation with body part thickness

A

Direct
(thicker = more PE)

73
Q

Photoelectric Effect relation with body part density

A

Direct
(more dense = more PE)

74
Q

Photoelectric Effect relation with atomic number of tissue

A

Direct
(higher atomic# = more PE)

75
Q

As kVp increases, the overall photoelectric effect increases, due to an increase in quantity of the polyenergetic beam. But, compared to transmission, the average PE events

A

decrease

(decrease in DA)

76
Q

A higher atomic number increases the likelihood of PE ____

A

Greatly

77
Q

Penetration from easy to hard

A
  1. Air
  2. Fat
  3. Water
  4. Muscle
  5. Bone
  6. Barium Sulfate
  7. Lead
78
Q

An increase in xray beam intensity = an overall ____ in ALL interactions.

A

Increase

79
Q

An increase in xray beam intensity = an overall increase in ALL interactions, a _____ in average compton interactions.

A

Decrease

80
Q

An increase in xray beam intensity = an overall increase in ALL interactions, a decrease in average compton interactions, a great ____ in average photoelectric interactions

A

Decrease

81
Q

An increase in xray beam intensity = an overall increase in ALL interactions, a decrease in average compton interactions, a great decrease in average photoelectric interactions, and an _____ in transmission through the pt.

A

Increase

82
Q

What modality is pair production used in?

A

Nuc med

83
Q

Does pair production occur in the diagnostic range of x-radiation?

A

no

84
Q

Pair production is important for

A

Positron Emission Tomography (PET)

85
Q

Pair production requires an xray photon energy of

A

> 1.02 mev

86
Q

Pair production steps

A
  1. photon escapes influence of orbital electrons, and interacts directly with the nucleus
  2. photon disappears, and 2 electrons appear in its place (one is positive/positron, and one in negative/negatron)
87
Q

What modality is photodisintegration used in?

A

Therapeutic Radiation Therapy

88
Q

Photodisintegration requires photon energy of

A

> 10 mev

89
Q

Photodisintegration steps:

A
  1. photon escapes interactions with orbital electrons and is absorbed by the nucleus
  2. nucleus emits nucleon or neclear fragments
90
Q

Does photodisentegration occur in the diagnostic range?

A

no

91
Q

Define Image Contrast

A

The degree of difference between the light and dark areas of a radiograph.

92
Q

Define Differential Absorption

A

The difference between the x-ray photons absorbed, and those that penetrate the body.

93
Q

What makes blacks, whites, and grays on a radiograph?

A

differential absorption

94
Q

What is subject contrast

A

The component of image contrast that is determined by the size, shape, and x-ray attenuating characteristics of the subject who is being examined and the energy of the beam.

95
Q

Factors affecting Subject Contrast

A

Low kvp
High z-number anatomy
Thicker part
Denser part

96
Q

What is attenuation?

A

The removal of any photons from the primary beam before striking the IR.

97
Q

What causes attenuation

A

Pt absorption
Compton Scatter that does not strike IR

98
Q

What is the technical term for photon aborption within the patient?

A

Differential Attenuation

99
Q

What is another way of describing “high contrast”?

A

Short Gray Scale

100
Q

What is another way of describing low contrast?

A

long gray scale

101
Q

What is the controlling factor of subject contrast?

A

kVp

102
Q

What is the controlling factor of image contrast?

A

LUT

103
Q

Describes the effects of kVp on the xray beam

A

Determines quality/penetrability

Influences contrast (increase kVp = decreased contrast)

104
Q

Describe the effects of kVp on differential absorption

A

Increasing kVp decreases the percentage of Differential Absorption

105
Q

Describe the effects of kVp on patient dose/absorption

A

Direct relationship

Size of beam has direct relationship to dose

106
Q

Briefly describe coherant scatter

A

An incident x-ray interacts with a target atom, the atom becomes excited then releases its excess energy as a scattered x-ray photon. The x-ray has a change in direction but not a change in energy.

107
Q

Briefly describe compton scatter

A

An incident x-ray interacts with an outer-shell electron, ejects it, and then ionizes the atom. This results in a Compton electron or recoil electron. The photon changes direction and has a reduction in energy.

108
Q

Briefly decribe photoelectric effect

A

The incident photon is absorbed by an inner (K-shell) electron, the electron gets ejected due to being in an excited state. Secondary radiation is produced from the cascading effect.

109
Q

Three types of compton scatter

A

back
Forward
side

110
Q

What determines the direction of a compton scattered photon?

A

where the photon interacts with the atom

111
Q

Uniform overall reduction of image contrast, due to compton, is called?

A

Noise

1613: Physics (3 decks)

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