Unit 2 Exam Flashcards

1
Q

What is applied to the cathode side of the tube during an exposure?

A

A large negative potential.

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2
Q

What is the process of producing an electron cloud referred to as?

A

Thermionic emission

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3
Q

Two reasons why Tungsten is an ideal target material

A

High Melting Point
High Z number (74)

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4
Q

Why are the tungsten filaments coated in thorium?

A

Thoriated tungsten burns off 2% more electrons.
More efficient thermionic emission process.

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5
Q

What does the acronym mAs stand for?

A

Milliampere Seconds

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6
Q

How do you convert seconds into milliseconds?

A

Move the decimal 3 places to the right

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7
Q

How do you convert milliseconds into seconds?

A

Move the decimal 3 places to the left

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8
Q

What happens to the patient’s dose if you cut the mA in half?

A

Patient dose is cut in half

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9
Q

What happens to the patient dose if you double the exposure time?

A

Patient does is doubled.

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10
Q

What is the definition of exposure time?

A

The amount of time potential difference (voltage) is applied to the tube.
Amount of time the patient is exposed to x-rays.

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11
Q

One reason why a shorter exposure time would be desired?

A

Motion Artifacts (image blur)

Moving children

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12
Q

List one reason why a longer exposure time would be desired.

A

Lateral T Spine

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13
Q

Reciprocity Law

A

Exposure to the IR will remain constant with adjustments to exposure time or mA if mAs remains constant.

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14
Q

AFS

A

Actual Focal Spot

Actual area of the target where incoming electrons hit.

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15
Q

What is the location of x-ray production?

A

AFS

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16
Q

EFS

A

Effective Focal Spot

Spot on patient where x-rays hit

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17
Q

99.8% of the energy created at the anode target is converted into?

A

Heat

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18
Q

What is the term that describes the way the beam travels after being created at the Anode?

A

Isotropic

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19
Q

Inherent Filtration

A

Filtration within the tube housing.

0.5mm Al equivalent

Glass

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20
Q

Added Filtration

A

Filtration outside the tube housing.

2.0mm Al equivalent

Mirror - 1.0mm Al

Al Filter - 1.0mm

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21
Q

Beam-Limiting Device

A

Variable-Aperture Collimator
Most common device

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22
Q

Beam - Restrictor Examples

A

Aperture Diaphragm
Cones/Cylinders

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23
Q

Off Focus Radiation

A

X-rays produced outside of the focal track

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24
Q

Leakage Radiation

A

X-ray photons escape the lead housing when the housing is compromised.

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25
Q

3 requirements for the production of x-rays

A
  1. Source of electrons
  2. Way to accelerate electrons
  3. Target
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26
Q

4 requirements for efficient x-ray production

A
  1. Source of electrons
  2. Way to accelerate electrons
  3. Vacuum
  4. Target
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27
Q

What is the controlling factor for beam quality?

A

kVp

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28
Q

What is the controlling factor for beam quantity?

A

mA

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29
Q

What material is the focusing cup made out of?

A

Nickel

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30
Q

Which electrode has a negative charge?

A

Cathode

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31
Q

Which electrode has a positive charge?

A

Anode

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32
Q

The cathode has a ____ negative potential during exposure.

A

The cathode has a large negative potential during exposure.

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33
Q

The focusing cup has a ____ negative charge in order to keep the electrons tightly bound.

A

The focusing cup has a low negative charge in order to keep the electrons tightly bound.

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34
Q

Thermionic Emission

A

Burning off of electrons due to the heating of a small coil of thoriated tungsten wire.

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35
Q

Why is the X-ray tube made of Pyrex?

A

To withstand high temperatures.

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36
Q

What is the x-ray tube surrounded by?

A

Oil Bath

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37
Q

What is the purpose of the oil bath?

A

To dissipate heat that is generated during x-ray production.

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38
Q

Most common type of x-ray tube failure?

A

Tungsten Filament Vaporization

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39
Q

What does the Cathode house?

A

The two filaments and the focusing cup.

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40
Q

What is the small filament (focal spot) used for?

A

Smaller body parts.

Greater spatial resolution

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41
Q

What is the large filament (focal spot) used for?

A

Larger body parts.

Needs more electrons that can be turned into x-ray photons.

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42
Q

What term describes when the filament is heated up to be “white hot”?

A

Incandescent

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43
Q

Why are the filaments coated in thoriated tungsten?

A

Thorium makes for a more efficient thermionic emission process by burning off 2% more electrons.

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44
Q

Why is the focusing cup made of Nickel?

A

Nickel has a high heat capacity

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45
Q

What type of charge does the focusing cup have?

A

Negative

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46
Q

What does the focusing cup house?

A

The filaments

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47
Q

What is the role of the focusing cup?

A

Focuses electrons that are produced by thermionic emission.

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48
Q

The focusing cup and the electrons both have a negative charge. Because of this, they _____ each other.

A

Repel

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49
Q

What do electrons form after thermionic emission?

A

Thermionic Cloud or Space Charge

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50
Q

What focuses the thermionic cloud/space charge?

A

Focusing cup

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51
Q

Electrons travel from the cathode to the anode by ____ _____

A

Kinetic energy

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52
Q

What is kinetic energy converted into once the electrons hit the anode?

A

X-rays

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53
Q

What percentage of kinetic energy from the electrons is turned into heat?

A

99.8%

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54
Q

What percentage of kinetic energy from the electrons is turned into useful x-rays?

A

<1%

55
Q

Is x-ray production considered efficient or inefficient?

A

Inefficient

56
Q

Dual Focus?

A

2 filaments within the tube

57
Q

mAs controls…?

A

Quantity/Intensity of x-rays in the primary beam.

58
Q

Formula for mAs

A

mA x S = mAs

59
Q

What is mAs?

A

The product of exposure time and x-ray tube current.

60
Q

What is the tube current?

A

The flow of electrons from the cathode to the anode.

61
Q

Does mAs have influence on penetrability or quality of the primary beam?

A

No. kVp.

62
Q

mAs and dose are ______

A

Proportional

63
Q

mA (milliamperage) is directly proportional to the ____ _______

A

mA (milliamperage) is directly proportional to the tube current.

64
Q

If mA is increased, what does that do to the electrons?

A

It increases the amount of electrons that are able to cross the tube to reach the anode.

65
Q

What is exposure time?

A

The amount of time that potential difference (voltage) is applied to the x-ray tube.

Amount of time the patient is exposed to x-rays.

66
Q

What units do we measure exposure time in?

A

Seconds or Milliseconds

67
Q

Exams typically require the ______ exposure time possible.

A

Shortest

68
Q

Why is a shorter exposure time desirable?

A

Eliminates motion artifacts
(Patient Movement and Image Blur)

69
Q

Lateral T-spine requires a longer exposure time, why?

A

Motion of the ribs will blur.

70
Q

Exposure time is ________ proportional to the number of electrons crossing the tube, and the number of x-rays generated.

A

Directly

71
Q

Exposure time is also directly proportional to ______

A

Dose

72
Q

Changes in the length of time that a tube is energized (exposure time) will affect ….

A

The total number of electrons crossing the tube.

73
Q

As a filament is heated over and over again, ________ ________ will create a film on the inside of the glass tube.

A

Vaporized Tungsten

74
Q

Once the deposits of tungsten coat the glass, what does it “make”?

A

A new target

75
Q

Electrons strike at the tungsten deposits on the glass tube, causing a ____.

A

Gas/Gassy Tube

76
Q

What is the effect of a gassy tube?

A

The tube is no longer a vacuum.

77
Q

Once exposure is engaged, a ______ ________ is applied to the anode.

A

Large voltage

78
Q

The anode always emits what type of radiation?

A

Infrared

79
Q

Potential Energy

A

Energy at rest

80
Q

What possesses potential energy?

A

Space Charge/Thermionic Cloud

81
Q

Kinetic Energy

A

Energy in motion

82
Q

Electrons have kinetic energy once …..

A

A large voltage is applied to the anode

83
Q

What is the target made out of?

A

A tungsten-coated disk, or a combination of tungsten and rhenium.

84
Q

What stops or slows down the electrons?

A

Target

85
Q

When are x-rays produced at the target?

A

When electrons are stopped or slowed down.

86
Q

What is the area of the target that is hit by incoming electrons?

A

Actual Focal Track (AFS)

87
Q

What is the melting point of Tungsten (W)?

A

6,192 degrees F

88
Q

Tungsten’s thermal conductivity is nearly equal to what other material?

A

Copper

89
Q

What is Radiation (heat)?

A

The transfer of heat by the emission of infrared radiation.

90
Q

Most of the heat is dissipated by _____ during exposure.

A

Radiation

91
Q

Which location of the tube is radiation?

A

Glowing hot anode

92
Q

What is Conduction?

A

The transfer of heat from one area of an object to another.

93
Q

Which locations are conduction occurring?

A

From the Anode, to the Rotor, to the Glass.

94
Q

What is Convection?

A

The transfer of heat by the movement of a heated substance from one place to another.

95
Q

What raises the temperature of the oil bath?

A

The heated glass enclosure

96
Q

Where is convection occurring?

A

From the Glass to the Oil Bath to the Tube Housing to the Room Air.

97
Q

How do you extend the life on an anode?

A

By rotating it.

98
Q

How fast will the anode spin during exposures?

A

3400 RPM to 10,000 RPM

99
Q

The heat created by electrons crashing into the ___ ____ will spread around the entire edge of the disk.

A

Focal Track

100
Q

The faster the anode rotates, the more ___ the tube can tolerate.

A

Heat

101
Q

What happens to the anode when it stops spinning?

A

Pitted Anode

102
Q

What does a pitted anode result in?

A

Image blur

103
Q

Why doesn’t pitting anode happen anymore?

A

The tubes have built-in safety devices that sense if the target is not spinning.

104
Q

Will an exposure be made if a (modern) anode is pitted?

A

No

105
Q

What does the term isotropic describe?

A

The way that the beam travels after being created at the anode (all directions)

106
Q

What is the lead housing?

A

It surrounds the x-ray tube except at the tube port

107
Q

What is the tube port?

A

A hole cut into the lead housing that allows x-rays to pass towards the patient.

108
Q

What is filtration for?

A

It removes low energy photons that only serve to increase patient dose (they go skin deep).

109
Q

Any x-ray tube that is capable of _______ is required to have 2.5mm Al equivalent, by law.

A

70 kVp or more

110
Q

What are the types of filtration?

A

Inherent and Added

111
Q

What is the aperture diaphragm?

A

The simplest beam-restricting device.

112
Q

What material is the aperture diaphragm made of?

A

Lead or a lead-lined metal

113
Q

Where does the aperture diaphragm go?

A

It attaches to the tube.

114
Q

The opening of the aperture diaphragm is designed to cover less than _____

A

The size of the image receptor.

115
Q

What are cones and cylinders?

A

Beam-Restrictors

Modifications of aperture diaphragms.

116
Q

What are cones and cylinders made of?

A

Metal

117
Q

What do cones and cylinders do?

A

Their distal end restricts the beam to the size and shape of the aperture modification.

118
Q

What is a variable-aperture collimator?

A

Beam-Limiting device
Most common

119
Q

The variable-aperture collimator has two stages of ______ ______.

A

Shuttering blades

120
Q

What does the First-Stage shuttering blade do?

A

Controls off-focus radiation.

121
Q

The first-stage shuttering blade has multiple collimator blades that protrude from the ______ into the _____

A

The first-stage shuttering blade has multiple collimator blades that protrude from the top of the collimator into the x-ray tube housing.

122
Q

What does the second-stage shuttering blade do?

A

Allows for a square or rectangular field.

Works in pairs and are independently controlled.

123
Q

What are the second-stage shuttering blade leaves made out of?

A

Lead that is 3mm thick

123
Q

What is off-focus radiation?

A

X-rays produced outside of the focal track.

124
Q

What is positive beam-limiting?

A

When the IR is loaded into the bucky tray, sensors in the collimator limit the beam size to the size and orientation of the IR.

125
Q

Where does inherent filtration take place?

A

Inside the tube housing.

126
Q

What is the value of inherent filtration?

A

0.5mm Al equivalent

127
Q

What part of the tube is the inherent filtration?

A

Glass

128
Q

Where does added filtration take place?

A

Outside of the tube housing.

129
Q

What is the value of added filtration?

A

2.0mm Al equivalent

130
Q

What are the two parts of added filtration?

A

Reflective surface of the mirror (Variable-aperture collimator)

Al filter that is placed between the tube housing and the collimator.

131
Q

What is the value of total filtration?

A

2.5mm Al Equivalent

132
Q

Criteria for Efficient X-ray Production

A
  1. Source of electrons
  2. Way to accelerate electrons
  3. Vacuum
  4. Target