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P1 Introductory science and methods > Diagnostic X-rays > Flashcards

Diagnostic X-rays Flashcards

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1
Q

What does a beam of high energy electrons from a heated filament bombard?

A

A positively charged heavy metal targets anode

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2
Q

What do electrons mostly react with?

A

Target’s orbital electrons producing heat (995), remaining electrons interact with target nuclei

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3
Q

How are X-rays formed?

A

Electrons changing direction and velocity within vicinity of . a heavy nucleus

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4
Q

What is deflection dependent on?

A

Nuclear charge (atomic number) of anode

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5
Q

What happens when there is direction and velocity change?

A

The electrons lose energy in the form of electromagnetic radiation producing a continuous x-ray spectrum

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6
Q

What is important in generation of X-rays?

A

Bremsstrahlung

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7
Q

What is the process of Bremsstrahlung?

A

A high speed electrons travelling in a material is slowed or completely stopped by forces of any atom it encounters

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8
Q

What happens as high speed electron approaches an atom?

A

It will interact with negative force from electron of atom, and it may be slowed or completely stopped

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9
Q

What happens if the electrons is slowed down?

A

It will exit material with less energy

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10
Q

What will be radiated as x-radiation of equal energy?

A

The energy used to slow electrons is excessive to atom

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11
Q

What is created at the surface of target?

A

A small proportion of x-ray

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12
Q

What type of x-ray are absorbed?

A

Those formed deeper within target material

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13
Q

Why does the energy transformation that yield x-rat radiation vary?

A

Bombarding electrons approach nuclei differently

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14
Q

What does the resulting x-radiation take the form of?

A

Continuous X-ray spectrum

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15
Q

What does the maximum beam energy Emax depend on?

A

Applied high voltage (Kv peak or Kvp) between cathode and anode

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16
Q

What results in x-ray spectrum curve with maximum?

A

The lowest energy photon are removed from spectrum since beam of x-ray leaving x-ray tube is filtered by glass envelope of x-ray tube

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17
Q

What creates orbital vacancies?

A

Collision between beam electrons and inner orbital electrons (K+L shells) of target

Energy of electrons > Binding energy of K-shell (BeK) or L shell (BEL)

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18
Q

What happens when electron vacancies are quickly filled?

A

Emission of characteristic radiation in form of line spectra

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19
Q

What is energy of characteristic radiation?

A

Difference between binding energies of electronic shell

BeK- BeL

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20
Q

How is characteristic X-ray emitted?

A

L electrons fills K-shell

K shell electrons is ejected

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21
Q

What is the most common material for anode target?

A

Tungsten

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22
Q

What range does line spectra occur at?

A

Roughly between the energies of 59keV and 69keV

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23
Q

What do majority of x-ray tubes employ?

A

Rotating anode to spread heat from electronic beam on to a larger surface for more effective anode cooling

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24
Q

How does x-rays originate?

A

Rectangular area (focal spot) of electron beam

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25
Q

What is x-ray tube?

A

vacuum tube that converts electrical input power into X-rays

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26
Q

What does the focal spot size influence?

A

Sharpness of x-ray image

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27
Q

Why are two focal spot necessary?

A

A second smaller spot is used for higher resolution

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28
Q

What does increasing high voltage Kvp increase?

A

Overall intensity of the continuous spectrum

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29
Q

What is intensity of x-ray beam proportional to?

A

Kilovoltage squared

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30
Q

What doubles X-ray beam intensity?

A

30% increase in Kvp

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31
Q

What increases with peak kilovoltage?

A

The effective energy, Eeff, of x-ray spectrum

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32
Q

What does the choice of kilovoltage determine?

A

Patient penetration and Image quality

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33
Q

Low kilovoltage

A

High contrast image (distinguish between soft tissue differenc)

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34
Q

What are easily absorbed?

A

Low energy x-ray photons

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35
Q

Higher kilovoltage

A

Increased penetration X-rays

Reduce contrast difference

36
Q

What does the characteristic radiation not change with?

A

Kilovoltage but its increasing in intensity, contributing about 10% for a tungsten anode

37
Q

What doesn’t alter the shape of x-ray spectra but intensity of x-ray beam increased proportionally to tube currents?

A

Increasing tube current

does not change effective energy

38
Q

What is the x-ray beam intensity Q a product of?

A
  1. Anode material atomic number
  2. The square of applied kilovoltage kvp
  3. Tube current mA

Q=ZKVP^2mA

39
Q

What is the intensity value Q influenced by?

A

Degree of beam filtration

40
Q

How does effective energy increase?

A

Adding filters which remove the lower x-ray energies that change the proportion of high to low energy photons in spectrum

41
Q

What significantly reduces the patient entrance dose?

A

Removing low energy radiation from beam

42
Q

What happens when x-ray beam goes through attenuator?

A

Mean or effective energy is increased due to prefential loss of low energy x-rays

43
Q

What does beam hardening cause?

A

Edges of object to appear brighter than centre, even if the material is same throughout

44
Q

What is a collimator?

A

A device which narrows a beam of particles or waves

45
Q

What are adjustable collimators used for?

A

Varying the overall x-ray beam size for different fields of view

46
Q

What is anode heated considerably by?

A

Electron beam

47
Q

What can x-ray photons be transmitted through?

A

Absorbing material unchanged

48
Q

What does the arrival of x-ray photon at imaging detector depend on?

A
  1. Photon absorption

2. photon scatter

49
Q

What goes to inner orbital electrons?

A

Incident photons

50
Q

K-electron

A

Closest to atomic nucleus

51
Q

L-electron

A

Orbit furthest away from nucleus

52
Q

What happens to the electron involved in photoelectric absorption?

A

Ejected from atom with a kinetic energy Ee=photon E

53
Q

What is required to free electrons from its original position?

A

Less energy

Ee=E-BE

54
Q

What is radiation dose?

A

Ejected electrons which expend energy close to place of origin and energy imparted to these is energy truly given to absorber

55
Q

What is empty K shell filled by?

A

Electrons from L or M electron orbit

56
Q

What is maximum absorption?

A

K-electron binding energy

57
Q

What is a contrast agent in vascular studies?

A

Iodine

58
Q

What has a mean energy of diagnostic X-ray spectrum?

A

K-shell BE

33keV

59
Q

What is photoelectric effect?

A

A form of interaction of x-ray/gamma photons with matter

60
Q

What does a low energy photon interact with?

A

Electron in the atom and removes it from its shell

61
Q

What does photoelectric effect contribute to?

A

Attenuation of x-ray beam as it passes through matter

62
Q

What is photoelectric absorption related to?

A
  1. Atomic number of attenuating medium
  2. The energy of the incident photon (E)
  3. physical density of attenuating medium (p)
63
Q

What is equation of PEA?

A

Z^3P/E^3

64
Q

Beam collimators

A

Light and X-ray field match each other

65
Q

When does compton effect occur?

A

Interaction of x-ray or gamma photon with free electrons or loosely bound valence shells electrons

66
Q

Compton effect

A

Incident x-ray photons interact with orbital electrons from outer shell which has binding energy which is negliably small

67
Q

What does the energy of scattered photon decrease with?

A

Increased scattered photon angle

68
Q

What does electron density show?

A

Difference between dense materials

69
Q

What does the direction of scattered radiation depend on?

A

Energy of incident beam

70
Q

What is scatter proportional to?

A

Number of free electrons + photon energy E

71
Q

What are examples of less dense material?

A

Water

Soft tissue

72
Q

What is the probability of compton effect directly proportional to?

A
  1. Number of outer shell electrons i.e. the electron density

2. Physical density of the material

73
Q

What is the probability of compton effect inversely proportional to?

A

Photon energy

74
Q

What does the probability of compton effect not depend on?

A

Atomic number

75
Q

As the photon energy increases

A

A forward angle of scatter is favoured

76
Q

What do scattered electrons produce?

A

Biological damage

77
Q

What does compton interaction dominate?

A

Photoelectric absorption for photon energies > 50kEV

78
Q

When is photoelectric effect mostly common at?

A

Low photon energies

79
Q

What relies to a greater extent on most diagnostic investigations?

A

Compton interactions

80
Q

When is the contrast of image better?

A

Imaging with lower energy X-rays

81
Q

What is the contrast C dependent on?

A

Thickness of target tissue

Difference in linear attenuation coefficients of target and uniform regions

82
Q

What do most x-ray interactions produce?

A

Energetic electrons

83
Q

What results in radiation dose?

A

Energy loss

84
Q

What are more likely to interact?

A

Low energy X-rays

85
Q

What is absorbed dose taken as ?

A

Physical indicator of biological tissue damage by ionizing radiation

86
Q

What does the exposure of x-ray lead to?

A

radiation-induced cancer

P1 Introductory science and methods (14 decks)

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