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Image Prod & Eval > Chapter 9- midterm > Flashcards

Chapter 9- midterm Flashcards

1
Q

What are the 3 conditions of producing an x-ray?

A
  • Free electrons
  • Acceleration of electrons
  • Deceleration of electrons
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2
Q

How are x-rays emitted from a tube?

A

To energize electrons and have them hit the metal target within an x-ray tube (anode)

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3
Q

How much energy is converted to photons when x-rays are produced?

A

0.5% of energy is converted to photons, remaining 99.5% is converted to heat

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4
Q

Why does the glass tube need to be vacuumed?

A

Vacuum removes the presence of air, which would cause the electrons to collide before reaching the anode and result in a loss of energy

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5
Q

What half of the tube releases electrons?

A

Cathode

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6
Q

What is thermionic emission?

A

When electrons are boiled off by the heating of the filaments

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7
Q

What is a filament made up of?

A

Tungsten alloy with Thorium, called thoriated tungsten

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8
Q

How far do the electrons travel within the tube?

A

1 inch from the cathode to the anode

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9
Q

How many volts are needed to move the electrons?

A

50,000 volts

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10
Q

What is responsible for moving the electrons?

A
  • Negative charge of the cathode, pushing negative electrons
  • Positive charge of the anode pulls the electrons
  • kV propels electrons to collide with anode
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11
Q

At what speed do the electrons travel?

A

Almost at the speed of light

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12
Q

What do electrons interact with once they’ve moved out of the cathode?

A

Spinning anode

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13
Q

What interactions occur at the anode?

A
  • Electron will go straight through the anode and nothing happens
  • Electron will die before it reaches the anode
  • Electron makes it near the nucleus of the atoms in the anode and produces a photon
  • Electron hits an electron of the atom in the anode which leaves its shell and nucleus produces a photon
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14
Q

What direction do x-ray photons travel?

A

Shoot down because of the angle of the anode

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15
Q

Where do the x-ray photons travel after hitting the anode?

A

Through a glass window of a tube

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16
Q

What are the two sides of the x-ray tube?

A

Cathode side and anode side (target material)

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17
Q

What is the positive side of the tube?

A

Anode

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18
Q

What is the negative side of the tube?

A

Cathode

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19
Q

Where does the production of x-rays start?

A

The filaments

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20
Q

How many filaments are part of the tube?

A

Two - one big and one small

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21
Q

How are electrons created from the filaments?

A

Milliamperage (electricity) is applied to the filaments

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22
Q

Where do the electrons go once emitted from the filaments?

A

Focusing cup

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23
Q

What is the benefit of a spinning anode?

A

Disperses the heat from the beam

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24
Q

What is the spot on the target where x-rays are emitted?

A

Focal spot

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25
Q

How fast does the anode spin?

A

3400 rpm

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26
Q

How many electrons are produced in a tube?

A

Quintillion

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27
Q

What is the stream of electrons moving across the tube called?

A

Cathode ray beam

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28
Q

What does a heterogenous x-ray beam mean?

A

Beam with varying energies

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29
Q

What determines the rate of thermionic emission?

A

The mA station

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30
Q

At what temperature does thermionic emission occur?

A

3700 degrees F

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31
Q

When does the mA kick in?

A

When the rotor button is pushed on the x-ray console

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32
Q

Which filament produces a better image?

A

Smaller filament

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33
Q

Why does a small beam produce a better image?

A

Because it produces a smaller focal spot which produces less blur in an image

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34
Q

What is space charge?

A

A cloud of electrons that form around a filament

35
Q

What are the main parts of a cathode?

A

The focusing cup and the filaments

36
Q

How does the size of the focal spot compare to the cathode ray beam?

A

Focal spot is always smaller than the beam

37
Q

How is a filament chosen?

A

By selecting a large or small focal spot

38
Q

What is the focusing cup made of?

A

Molybdenum or nickel

39
Q

What is the melting point of the filament?

A

6200 degrees farenheit

40
Q

How many x-rays come out of a patient?

A

2% come out and 98% get stuck

41
Q

How much smaller is the focal spot that the cathode ray beam?

A

1/20th the size of the filament
- .5mm for small filament
- 1 mm for large filament

42
Q

What is a grid controlled tube?

A

A way to turn exposure on and off quickly by switching the polarity of a focusing cup

43
Q

What is the anode made of?

A

Molybdenum and tungsten-rhenium alloy focal tract

44
Q

What quality is needed in metal to create x-rays?

A

High melting point and high atomic number

45
Q

What is an anode disc attached to?

A

Molybdenum shaft that ends in a copper cylinder

46
Q

What is the atomic number of Tungsten?

A

74

47
Q

What is the atomic number of Rhenium?

A

75

48
Q

What is the symbol for Tungsten?

A

W

49
Q

What does a smaller focal spot provide in an image?

A

Higher spatial resolution due to a more focused beam

50
Q

What is the line focus principle?

A

Based on the fact that there is an angle on the anode. The smaller the anode angle, the smaller the effective focal spot (ray)

51
Q

What is the glass envelope of the tube?

A

Glass that surrounds the anode and cathode

52
Q

What is x-ray tube failure?

A

A malfunction of an x-ray tube due to use over time

53
Q

What is tube arcing?

A

Tungsten material vaporizes over time which builds up on the tube window, causing the electrons to arc when travelling and reducing image quality

54
Q

When is arcing less likely to occur?

A

With metal enclosed tubes

55
Q

What are other forms of tube failures?

A
  • Bearing warping which impacts focal spot
  • Filament burnout
56
Q

How is heat measured?

A

In Heat units

57
Q

What is the formula for heat units?

A

HU = kVp x mA x s

58
Q

How much stronger are three phase & high frequency generators?

A

1.4 times

59
Q

What is the heat unit formula for high frequency or 3 phase?

A

HU = 1.4 x kVp x mA x s

60
Q

What does a more efficient generator produce vs less efficient?

A

More photons closer to the amount set in terms of kVp

61
Q

How can you extend tube life?

A

Performing a tube warm up when the machine hasn’t been utilized for a while

62
Q

What is a good warm up rate?

A

3 exposure 5 seconds apart using 200 mA, 1 second and 70 kVp

63
Q

What is the Space Charge (SC) effect?

A

When the space charge becomes larger and the repulsive force between the charge and the filament increases

64
Q

What happens when the repulsive force of the space charge exceeds that of the filament?

A

The electrons from the space charge return to the filament and inhibit additional electrons from being able to join the space charge

65
Q

What happens to the space charge when high mA settings are set?

A

The repulsive forces of the space charge can exceed the repulsive forces of the filament current

66
Q

What happens to the size of the space charge when the SC effect is in play?

A

The size of the space charge becomes limited

67
Q

When the size of the space charge is limited what effect will increasing the mA have on it?

A

No effect, increasing the mA will not increase the number of electrons in the charge

68
Q

What corrects for the problem of the Space Charge effect?

A

The space charge compensator

69
Q

What is the area of the anode which is struck by electrons called?

A

Target

70
Q

What two things are created when the electrons bombard the target?

A

x-rays and heat

71
Q

What size is the focal spot of specialized tubes?

A

0.1 mm

72
Q

How does a grid controlled tube work?

A

Utilizes oblique repulsion from a negatively charged mesh in front of the filaments

73
Q

What does the grid controlled tube prevent?

A

Electrons from escaping

74
Q

What component of Tungsten and Rhenium increase probabilities of interactions?

A

Proton rich nuclei, which help pull electrons toward the anode

75
Q

How fast can anodes spin in CT machines?

A

10000 rpm

76
Q

What does moving the anode allow?

A

For the focal spot to change

77
Q

When does the rotation of the anode start?

A

When the rotor is depressed prior to the actual exposure

78
Q

Which focal spot will get hotter?

A

A smaller focal spot because it has a more focused beam of electrons

79
Q

What is the advertised focal spot known as?

A

Nominal focal spot

80
Q

Which focal spot requires lower mA?

A

Small focal spot

81
Q

What does prepping first provide more control over?

A

Stopping the exposure if you need to

82
Q

What does the heat storage capacity of an anode depend on?

A

Disc diameter and rotational speed

83
Q

What is the temperature of the filament directly related to?

A

The quantity of x-rays produced

Image Prod & Eval (10 decks)

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