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Radiologic Exposures > Final Review : Xray interactions > Flashcards

Final Review : Xray interactions Flashcards

1
Q

-Reduction in number of xray photons in beam
- results of xray photons interacting with matter (interacts happen at the atomic level)

A

Attenuation

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2
Q

photons that interact with the whole atom

A

low energy photons

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3
Q

photons that interact with orbital electrons

A

moderate electrons

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4
Q

photons that interact with nucleus

A

high energy photons

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5
Q

Xrays can undergo any of three processes

A

-transmission without any energy
-total absorption
-penetration with loss of energy
-interactions can occur with: entire atom, orbital electrons, atomic nucleus

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6
Q

-anatomic tissue absorbs and transmits xrays differently based on their composition (anatomic number and tissue density)
-bone absorbs more xrays than muscle
-attenuation:the primary xray beam loses some of its energy (number of photons) as it interacts with anatomic tissue (absorption, scattering)

A

Differential Absorption

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7
Q

Three essential aspects of tissues will determine their attenuation properties and the resulting subject contrast

A

tissue thickness
tissue density
tissue atomic number

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8
Q

Electrons close to nucleus are tightly bound to nucleus due to location and positive charge of nucleus

A

orbital electrons

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9
Q

electrons further away are weakly attracted to nucleus and easily removed

A

creating ionization

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10
Q

when the primary xray beam interacts with anatomic tissues. Three processes occur during attenuation of the xray beam

A

absorption
scattering
transmission

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11
Q

If the incoming xray photon passes through the atomic part without any interaction with the atomic structure, what is it called?

A

Transmission

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11
Q

-a static energy from positive charge of the nucleus
-dependent upon atomic number of element

A

Electron binding energy
(higher atomic number yields higher binding energies and inner shell electrons have higher binding energy due to proximity to positively charged nucleus)

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11
Q

Total energy of electron is a function of which two combined energies

A

binding and kinetic

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11
Q

Dynamic energy of electron due to its relative position in the electron orbital cloud

A

electron Kinetic energy
-electrons in outer shell posses higher kinetic energy
-electrons in inner shells (K, L, M) have lower kinetic energy but higher binding energies

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12
Q

Interactions between Xray and Matter

A

coherent scattering
photoelectric absorption
compton scattering

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13
Q

Complete absorption of the incoming photon :
-xray ionizes atom
-low energy secondary xray photon created

A

Photoelectric Effect

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14
Q

what is the probability of photoelectric effect dependent on

A

the energy of the incoming xray photon and tissue atomic number

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15
Q

During what interaction is the energy of the primary beam deposited within the atoms comprising the tissue

A

During absorption

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16
Q

what interaction occurs when an incoming photon loses some but not all of its energy then changes its direction

A

Compton effect

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17
Q

It can occur within all diagnostic xray energies and is dependent only on the energy of the incoming photon, not the atomic number of the tissue

A

Compton Effect

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18
Q

What happens to the number of compton interactions when there is higher kvp

A

Higher kvp reduces the number of interactions overall, but the number of compton interactions increases in comparison to the number of photoelectric interaction

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19
Q

What does an increase in atomic number and absorption do to transmission

A

decreased transmission

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20
Q

Steps for photoelectric absorption:

A
  1. Incident electron passes near K or L shell electron of a patients atom

2 The incident photon is completely absorbed and ejects the inner shell electron (photoelectron)

  1. A vacancy is created in the orbital shell
  2. The ionized atom attempts to return to the normal state by filling the vacancy with the outer shell electrons
  3. The movement of the outer shell electrons creates a characteristic cascade
  4. Potential energy of each orbital electrons movement is converted to a low energy characteristic photon
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21
Q

What four words are associated with Photoelectric absorption

A

**diagnostic value
**absorption
**Inner shell
**characteristic cascade

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22
Q

what two interactions have a characteristic casecade

A

characteristic in the tube and photoelectric in person

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23
Q

photoelectron energy can be determined with the following equation:

A

Ei=Eb + Eke

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24
Q

Photoelectron characteristics

A

kinetic energy
mass
reabsorbs quickly

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25
Q

-vacancy filled by outer shell electron
-electron undergoes change in energy level (emits characteristic photon and energy of photon determined by difference in binding levels)

A

Characteristic Cascade

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26
Q

-Radiation that originated from irradiated material outside xray tube
-production similar to characteristic xray production within target
-Characteristic photons emitted from atoms of patient after PE absorption interaction

A

Secondary Radiation Energy

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27
Q

what type of secondary radiation results with low atomic number in tissue

A

low energy secondary radiation

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28
Q

what type of secondary radiation results in higher atomic number with contrast agents

A

Higher energy secondary radiation

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29
Q

incident electron energy (Ei) must be greater than or equal to binding energy (Eb) of inner shell electron
Example:
Ei = 40 keV
Eb= 45 keV

A

No photoelectric interaction will take place here

30
Q

Incident photon energy (Ei) and inner shell electron binding energy (Eb) are close to eachother
-as photon energy increases, chance of PE interaction decreases dramatically (inverse relationship)
example:
Ei=40 keV
Eb=36 keV

A

PE interaction likely to occur

31
Q

Given the follow which interaction has a probability of happening :
Ei=120 kev
Eb=36 kev

A

Probability of transmission higher than PE absorption interaction

32
Q

PE absorption interaction more likely to occur in elements with higher atomic number and what does that do to the binding energy

A

Therefore higher binding energy of inner shell electrons

33
Q

what is the relationship when the increased atomic number has a dramatic impact on amount of PE absorption

A

direct cubed relationship

34
Q

what is the relationship betwen PE absorption when the atomic number is doubled

A

increases change of PE absorption interaction by factor of 8

35
Q

If the atomic number is high or low what shell is being interacted with

A

-low atomic number atoms experience PE absorption interaction with K shell
-Higher atomic number atoms experience PE absorption interaction in K, L, or M shell

36
Q

this interaction is crucial to the formation of the of the radiographic image and is responsible for the production of contrast on the radiographic image

A

Photoelectric effect

37
Q

Photons can go through, transmit

A

Radiolucent

38
Q

All absorbed, no transmission, cant go through

A

Radiopaque

39
Q

3 words associated with coherent

A

-low energy
-no clinical value
-scatter radiation

40
Q

-incident and scattered same wavelength
-same energy incoming, same outgoing
-non-ionizing, no removal of electrons

A

Coherent Scatter

41
Q

During attenuation of the beam what is photoelectric effect responsible for?

A

total absorption of the incoming xray photon

42
Q

This term refers to any xray photon which has changed direction from the direction of the primary beam

A

Scatter

43
Q

how much percentage of scatter xray photons orginate from Compton interactions in the patient

A

99%

44
Q

Where do Compton and photoelectric interactions occur

A

-Compton occurs only in outer shells of an atom
-photoelectric interactions occur only in the inner most shell of an atom

45
Q

Factor affecting beam attenuation

A

Tissue thickness- xrays attenuated reduced by 50% for each 4 to 5 cm of tissue thickness

Type of tissue- tissues composed of higher atomic number will increase beam attenuation

Tissue density- increasing the compactness of the atomic particle will increase beam attenuation

xray beam quality- higher kvp increases the energy of the xray beam and will decrease beam attenuation

46
Q

what type of radiation is composed of transmitted and scattered radiation

A

remnant or exit

47
Q

what is it called when scatter radiation reaching the image receptor creates unwanted exposure

A

Fog

48
Q

True or false
most secondary radiation is scattered

A

true

49
Q

Refers to that secondary radiation which has been emitted in a diraction different than the orginal xray beam

A

scatter radiation

50
Q

refers to any radiation resulting from interactions within the patient

A

secondary radiation

51
Q

-No clinical value
-involves low energy photons below 10 kev
-Thompson-single outer shell electron
-Rayleigh- all electrons of atom

A

Coherent Scatter

52
Q

-electrons excited and vibrate at photon frequency
-no electrons ejected
-no ionization taken place
-atom stabilizes itself by releasing photon equal in energy to incident photon but in a different direction

A

Coherent scatter

53
Q

what is your patient dose

A

photoelectric

54
Q

what is your occupational dose

A

comptom

55
Q

bi products for Compton

A

recoil electron and scatter photon

56
Q

-incident electron interacts with outershell, loosely bound electron and ejects it (recoil electron)
-ion pair formed
- scattered photon redirected at some angle with a loss of kinetic energy
-higher kev photons, scattering more forward direction
-outershell
-form of scatter

A
57
Q

what interaction has one incoming and two leaving

A

compton

58
Q
A
59
Q

-Photon transfers some of its kinetic energy to recoil (compton) electron and continues on in a different direction
-incident photon energy is distributed between recoidl electron and scattered photon

A

Compton Scatter

60
Q

-Recoil electron travels until it fills vacancy in another atom
-scattered photon continues to interact until absorbed photoelectrically

A

Compton Scatter

61
Q

Source of occupational exposure and radiation fog

most scatter travels in foward direction

backscatter

A

Compton Scatter

62
Q

which interaction is predominant in higher Z# materials

A

Photoelectric

63
Q

Which interaction is predominant in soft tissues

A

Compton

64
Q

PE Versus comptom highly dependent on two factors

A

-incident photon energy
-atomic number of target atom

65
Q

with attenuated beam:
as kvp increases what happens to PE and compton

A

PE absorption decreases
Compton effect increases
increases percentage of scatter and decreases percentage of absorption

66
Q

which interaction predominates in two circumstances:
low energy ranges
in elements with higher atomic numbers

A

PE

67
Q

This interaction typically predominates within diagnostic xray energy range

A

Compton

68
Q

When PE absorption predominates:

A

-resulting imaging will have higher contrast
-clearly seen with film/screen imaging
-not obvious with digital processing
low kvp and high mAs

69
Q

When compton predominates:

A

-resulting image will have lower contrast
-clearly seen with film/screen imaging
-not obvious with digital processing
- high kvp and low mas produce more Compton interactions but less patient exposure

70
Q

What happens to
beam attenuation
absortion
transmission
when tissue thickness increases
and decreases

A

increase:
increase attenuation
increase absorption
decrease transmission

decrease
decrease attenuation
decrease absorption
increase transmission

71
Q

What happens to
beam attenuation
absortion
transmission
when tissue atomic number increases
and decreases

A

increase :
increase attenuation
increase absorption
decrease transmission

decrease
decrease attenuation
decrease absorption
increase transmission

72
Q

What happens to
beam attenuation
absorption
transmission
when tissue density increases
and decreases

A

increase :
increase attenuation
increase absorption
decrease transmission

decrease
decrease attenuation
decrease absorption
increase transmission

73
Q

What happens to
beam attenuation
absorption
transmission
when xray beam quality increases
and decreases

A

increase:
decrease attenuation
decrease absorption
increase transmission

decrease:
increase attenuation
increase absorption
decrease transmission

74
Q

Steps of Coherent interaction:

A
  1. A low energy photon approached an atom inside the patient
  2. the electron is momentarily excited
  3. the unstable atom re-emits the xray photon to regain stability
  4. the re-emitted photon travels in a new direction with no loss of energy
75
Q
A

Radiologic Exposures (11 decks)

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