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Imaging Maintenance and Equipment > M Part II > Flashcards

M Part II Flashcards

1
Q

-special type of diode (anode & cathode)
-converts electrical energy to EM energy

A

X-ray Tube

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2
Q

any tube with two electrodes

A

Diode

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3
Q

-consists of two perpendicular sets of ceiling mounted rails
-most frequently used
-allows both longi and transverse travel of x-ray tube

A

Ceiling-Support System

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4
Q

when x-ray tube is centered above examination table at the standard SID

A

Preferred Patient Pos’n

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5
Q

-consists a single column with rollers at each end
-the x-ray tube slides up and down the column as the column relates
-variation: single floor support system

A

Floor-to-ceiling Support System

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6
Q

-C-shaped and ceiling mounted system
-provides very flexible x-ray tube positioning

A

C-arm support system

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7
Q

variations for C-arm support system

A

L-arm and U-arm

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8
Q

lead -lined metal container into which the x-ray tube is fitted

A

Protective Housing

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9
Q

3 Functions of Protective Housing

A
  1. Insulation (diala oil) - against electric shock
  2. Thermal cushion - to dissipate heat
  3. Mechanical support - for the tube and protect from damage caused by rough handling
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10
Q

Properly designed protective housing reduces level of leakage radiation to less than [..]

A

100mR/hr at 1 m

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11
Q

emission with intensity in all directions

A

Isotropic Emission

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12
Q

a thin section of a glass/metal envelope that which useful beam emerges
size: 5 cm²

A

Window

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13
Q

x-rays emitted through the window

A

useful beam/primary radiation

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14
Q

x-ray that escape through protective housing

A

leakage radiation

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15
Q

it contains x-ray tube and its components

A

glass/metal enclosure

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16
Q

glass enclosure composition able to withstand tremendous heat

A

pyrex glass

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17
Q

disadvantages of glass enclosure

A

more likely to fail
lesser tube life

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18
Q

maintain constant electric potential b/w electrons of the tube current and enclosure

A

metal enclosure

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19
Q

advantages of metal enclosure

A

less likely to fail
longer tube life

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20
Q

negative side of x-ray tube

A

cathode

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21
Q

2 primary parts of cathode

A

filament
focusing cup

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22
Q

a coil of wire that emits electrons when it is heated

A

filament

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23
Q

composition of filament

A

thoriated tungsten

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24
Q

purpose of 1-2% thorium in filament

A

enhance efficiency of thermionic emission
prolongs tube life

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25
Q

Atomic no. [W]

A

74

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26
Q

Atomic no. [W]

A

74

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27
Q

melting point of W

A

3410 degrees celsius

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28
Q

purpose of W in filament

A

-provides higher thermionic emission
-does not vaporize easily

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29
Q

T/F If enclosure is vaporized, it can cause arcing and lead to tube failure

A

T

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30
Q

most common type of tube failure

A

tungsten vaporization with deposition

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31
Q

metal shroud that surrounds filament

A

focusing cup

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32
Q

effectiveness of focusing cup is determined by

A

-size and shape
-its charge
-filament size and shape
-pos’n of filament

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33
Q

serves as a grid (exposure switch) in grid controlled x-ray tube

A

focusing cup

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34
Q

The x-ray tube current is adjusted by controlling [..]

A

filament current

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35
Q

cloud of electron

A

space charge

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36
Q

a phenomenon of the space charge that makes it difficult for subsequent electrons to be emitted by filament bc of electrostatic repulsion

A

space charge effect

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37
Q

T/F Thermionic emission at low kVp and high mA can be space charge limited

A

T

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38
Q

filament current that has risen to its maximum value bc all available electrons have been used

A

saturation current

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39
Q

X-ray tube at saturation current emission is [..]

A

limited

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40
Q

a region of the anode target in which electrons interact to produce x-rays
-actual x-ray source

A

filament spot

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41
Q

filament spot sizes
small: [..]
large: [..]
shape: [..]

A

0.1-1mm
0.3-2mm
circular (preferred) / double banana

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42
Q

important for high resolution magnification radiography and mammography

A

round focal spot

43
Q

used when small body parts are imaged and when better spatial resolution is required
assoc with small filament

A

small focal spot

44
Q

limiting factor of small focal spot

A

the heating of target is concentrated onto smaller area

45
Q

used when large body parts are imaged
assoc with large filament

A

large focal spot

46
Q

positive side of XRT
conducts electricity, radiates heat and contains target

A

anode

47
Q

two types of of anode

A

stationary
rotating

48
Q

3 functions of anode

A

electrical conductor
mechanical support for the target
thermal dissipator

49
Q

3 most common anode materials

A

copper
molybdenum
graphite

50
Q

copper atomic no.

A

29

51
Q

molybdenum atomic no.

A

42

52
Q

difference if Mo and Graphite to tungsten

A

lower mass density
make anode lighter and easier to rotate

53
Q

used when high tube current and power are not required

A

stationary anode

54
Q

imaging systems using stationary anode

A

dental x-ray imaging system
portable x-ray imaging system

55
Q

the area of the anode struck by the electrons from the cathode

A

target

56
Q

composition of target

A

stationary - alloy embedded in the copper anode
rotating - entire rotating disk, alloying the W with Rhenium

57
Q

purpose of rhenium in target

A

additional mechanical strength to withstand stresses (high-speed rotation)
the high effects of high repentive expansion and contraction

58
Q

mammographic target composition

A

Mo 42
Rh 41

59
Q

material of choice for target

A

Tungsten W

60
Q

3 main reasons for using W for target

A
  1. atomic no. : high Z results to high efficiency x-ray production and high energy x-ray
  2. thermal conductivity: efficient material for dissipating heat
  3. high melting point: 3410 deg C compared to Cu = 3000 deg C
61
Q

it allows the electron beam to interact with a much larger target area

A

rotating anode

62
Q

rpm of rotatong anode

A

3 600 - 10 000 rpm

63
Q

T/F Higher tube currents and shorter exposure times are possible with the rotating anode

A

T

64
Q

shaft between anode and rotor

A

anode stem

65
Q

anode stem composition

A

molybdenum

66
Q

characteristic of Mo as anode stem

A

poor heat conductor

67
Q

used to turn the anode

A

Electromagnetic Induction Motor

68
Q

2 Principal Parts of EM Induction motor

A

stator and rotor

69
Q

located outside the enclosure
secondary coil windings/electromagnets

A

stator

70
Q

located inside glass envelope
rotating part (shaft)

A

rotor

71
Q

time it takes the rotor to rest after use
approx. 60s

A

coast time

72
Q

-as the target angle decreases, the effective focal spot also decreases
-design incorporated into XRT target
-allows large area for heating while maintaining a small focal spot

A

Line Focus Principle

73
Q

result of line focal principle

A

effective focal spot much smaller than the actual focal spot

74
Q

line focal principle Limiting Factor

A

ability of the cone of x-ray produced to adequately cover the largest field size used

75
Q

the area projected onto the patient and image receptor

A

effective focal spot/ effective target area

76
Q

area on the anode target that is exposed to electrons from the tube current

A

actual focal spot

77
Q

consequence of line focus principle

A

anode heel effect

78
Q

describe ANODE HEEL EFFECT

A

absorption of x-rays in the heel of target
the smaller the anode angle, the larger the heel effect

79
Q

results of ANODE HEEL EFFECT

A
  1. smaller effective focal spot
  2. radiation intensity on the cathode side (120%) of the x-ray field is greater than that on anode (75%)
80
Q

important consequences of ANODE HEEL EFFECT

A
  1. thicker part (cathode side), thinner part (cathode side)
  2. larger effective focal spot size (cathode)
    smaller effective focal spot size (anode)
81
Q

the imaginary line generated by the center most x-ray in the bream

A

central ray

82
Q

describe OFF FOCUS RADIATION/EXTRA FOCAL X-RAYS

A

x-rays produced in anode but not at focal spot

83
Q

Results of OFF FOCUS RADIATION/EXTRA FOCAL X-RAYS

A
  1. increases skin dose
  2. reduces image contrast
  3. exposure of tissue that was intended to be excluded by collimator
84
Q

OFF FOCUS RADIATION/EXTRA FOCAL X-RAYS geometric solutions

A
  1. designing a fixed diaphragm in the tube housing near the window of the XRT
  2. Metal enclosure XRT
85
Q

Factors affecting XRT life
increased:

A

-minimum radiographic factors mA, kVp and exposure time
-faster IR

86
Q

Factors affecting XRT life
decreased:

A

excessive heat

87
Q

3 ways of heat dissipation

A

radiation
conduction
convection

88
Q

transfer of heat by emission of infrared radiation

A

radiation

89
Q

transfer of energy from one area of an object to another

A

conduction

90
Q

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

A

convection

91
Q

causes of tube failure

A
  1. a single excessive exposure
  2. long exposure time causes excessive heating of the anode
  3. vaporization of filament
92
Q

a single excessive exposure
causes: [..]

A

pitting and cracking

93
Q

long exposure time causes excessive heating of the anode
result: [..]

A

damage to the bearings on the rotor assembly

94
Q

long exposure time causes excessive heating of the anode
causes: [..]

A

warping and rotational friction of the anode

95
Q

vaporization of filament
causes: [..]

A

arcing

96
Q

T/F The most frequent cause of abrupt tube failure is electron arcing from filament to enclosure due to vaporized tungsten

A

T

97
Q

it guides and aids the RT in using x-ray tubes and acceptable exposure levels to maximize x-ray tube life

A

X-ray tube rating charts

98
Q

-most important XRT rating charts
- it conveys which radiographic technique are safe and unsafe for XRT operation

A

Radiographic Rating Charts

99
Q

used to detrmine the thermal capacity of an node and its heat dissipation characteristics
also used to determine the length of time required for complete cooling after any level of heat input

A

anode cooling chart

100
Q

heat thermal energy
SI unit: [..]
British units: [..]
X-ray Applications: [..]

A

calories
joules
heat units (HU)

101
Q

single phase
formula

A

HU = kVP x mA x s

102
Q

three-phase 6-pulse
formula

A

HU = 1.35 x kVp x mA x s

103
Q

three-phase 12-pulse
formula

A

HU = 1.45 x kVp x mA x s

104
Q

used precisely in same way as anode cooling chart
-complete cooling: 1-2 hrs

A

housing cooling chart

Imaging Maintenance and Equipment (6 decks)

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