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:] > LRA-222 Week 1 Tube Components > Flashcards

LRA-222 Week 1 Tube Components Flashcards

1
Q

what specialties in radiology uses x-rays?

A
  • radiography
  • fluoroscopy
  • mammography
  • computed tomography
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2
Q

define thermionic emissions

A
  • boiling off electrons
  • heating up the filaments (that’s housed in the focusing cup) and creating a cloud of electrons
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3
Q

define cathode

A
  • where electrons are located
  • negatively charged
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4
Q

define anode

A
  • positively charged
  • absorbs electrons and creates x-rays
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5
Q

define glass envelope

A
  • creates an air free vacuum around the anode and cathode
  • made up of borosilicate glass
  • protects tube from oxidation and corrosion
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6
Q

tube/metal housing

A
  • prevent x-rays from being emitted throughout the exam room
  • absorbs x-ray photons
  • keeps leakage radiation to a max of 0.88 mGy/hr
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7
Q

define space charge

A
  • cloud of electrons
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8
Q

define space charge effect

A
  • at 1,000 mA, no more electrons can be forced out of the filament
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9
Q

define dual focus

A
  • 2 cathode filaments
  • small filament
  • large filament
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10
Q

how many filaments are in the cathode?

A
  • two
  • small and large filament
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11
Q

name the factors of a small filament

A
  • used for small mA
  • has a small heat capacity
  • small body parts
  • used for small body parts
  • high spatial resolution
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12
Q

name the factors of a large filament

A
  • low spatial resolution
  • large mA
  • used for large body parts
  • large exposures
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13
Q

where are the filaments located?

A
  • both filaments are housed in the focusing cup
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14
Q

define focusing cup

A
  • to focus the electron beams (so they go in a straight line)
  • narrow electron beam = increase in spatial resolution
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15
Q

how does the focusing cup keep a narrow electron stream?

A
  • the focusing cup is also negatively charged
  • because of the charge, they repel the electrons that are produced, resulting in a narrow stream
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16
Q

what are the 2 types of anodes?

A
  • stationary anode
  • rotating anode
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17
Q

define stationary anode

A
  • immobile
  • when hit with electrons, it only hits one part of the anode (creating pitting)
  • simple design
  • low heat capacity
  • low exposures
  • commonly used in dental offices
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18
Q

define rotating anode

A
  • rotating disk
  • electrons hit multiple spots (large surface area)
  • increases heat capacity
  • complex design
  • high heat capacity
  • high exposures
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19
Q

why are stationary anodes not ideal in general radiography?

A
  • because the electrons only hit one spot, it easily damages the anode, resulting in a short duration
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20
Q

define induction motor

A
  • turns the another without contacting the actual anode
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21
Q

what are the different parts of the induction motor?

A
  • stator
  • rotor
  • bearing
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22
Q

define stator

A
  • uses electromagnets
  • activated in series to induce turning of the rotor
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23
Q

define rotor

A
  • attached directly to the anode
  • rotates
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24
Q

define bearings

A
  • in between the rotor
  • low friction spheres that allow for free rotation of the rotor
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25
Q

define the anode heel effect

A
  • phenomenon that effects the intensity of the x-ray beam
  • anode side of the tube will be weaker than the cathode side
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26
Q

what are the angles in an anode angle?

A
  • anode angle ranges from 6 to 20 degrees
27
Q

how does the angle of the anode affect the heel effect?

A
  • with a smaller angle (6 degrees), less photons will be able to pass through (absorb more photons)
  • with a larger angle (20 degrees), more photons will be able to pass through
28
Q

what happens when the anode angle decreases?

A
  • increases anode hell effect
  • decreases intensity
29
Q

when anode angle decreases -

A

anode hell effect increases

30
Q

when SID decreases -

A
  • anode heel effect increases
31
Q

when field size increases -

A
  • anode heel effect increases
32
Q

define actual focal spot

A
  • physical area of the anode where electrons concert into x-rays
  • electron stream
  • where heat is created
33
Q

define line focus principle

A
  • relationship between actual focal spot and effective focal spot (in the anode)
  • affects heat capacity, spatial resolution, and beam coverage
34
Q

define why is a large focal spot desired?

A
  • helps spread out the heat
35
Q

define effective focal spot

A
  • width of the x-ray beam as it’s projecting toward the patient
  • the pathway where the x-ray photons travel
  • directly affects the creation of penumbra (blur) and spatial resolution
36
Q

when we have a small effective focal spot it-

A

decreases penumbra and increases spatial resolution

37
Q

when we have a large effective focal spot it-

A

increases penumbra and decreases spatial resolution

38
Q

what is the desired goal with the focal spots?

A
  • we want a large focal spot with a small effective focal spot
39
Q

when positioning a patient, where should the least dense body part be placed?

A
  • least dense portion should be placed on the anode side
40
Q

with a large actual focal spot, heat capacity -

A
  • increases
41
Q

with a small effective focal spot, spatial resolution -

A
  • increases
42
Q

what are the factors of a small anode angle?

A
  • very narrow effective focal spot
  • well aligned beam
  • high spatial resolution
  • more heat
  • less beam coverage
  • small field size
  • smaller actual focal spot
  • smaller exposure factors (mAs, kVp)
  • smaller effective focal spot (increase spatial resolution)
  • increased heel effect
  • 6 degrees
  • used in small body parts
  • used for extremities, dental, and mammography imaging
43
Q

what are the factors of a large anode angle?

A
  • large actual focal spot
  • large exposure factors (mAs, kVp)
  • larger effective focal spot
  • low spatial resolution
  • larger field size
  • large anode angle
  • large body parts
  • large techniques
  • larger image details
  • used in abdomen, pelvis, spine (thoracic and lumbar)
44
Q

define off focus radiation

A
  • when the x-ray photons get away from the actual focal spot of the anode
  • electrons that collide with different parts of the tube, eventually escape the tube, creating an “Off focus radiation”
45
Q

true or false: off focus can interfere with processing the digital image

A

true

46
Q

how does off focus radiation affect patient dose?

A
  • patient dose increases because it captures parts outside of the collimated area
47
Q

with an off focus principle, it -

A
  • increases patient dose
  • decreases spatial resolution
  • decreases contrast
48
Q

true or false: the decrease of spatial resolution when off focus radiation is processed in a digital image, is due to the failure of histograms

A

true

49
Q

how does off focus radiation impact an image?

A
  • disturbs the brightness and contrast of the image, making it harder to interpret
50
Q

how can we fix off focus radiation?

A

shuttering

51
Q

define shuttering

A
  • “cutting” off the bright portion of the collimation
  • known as “post processing collimation”
52
Q

when should post processing collimation be used?

A
  • only to remove the visibility of large regions of brightness
53
Q

true or false: never use post processing radiation to eliminate anatomical information

A

true

54
Q

define tube loading

A
  • heat created within the x-ray tube (especially at the anode)
55
Q

what happens if the x-ray tube is overheated or overloaded?

A
  • it can cause the anode to melt or rupture the x-ray tube
56
Q

define heat units

A
  • heat created within the x-ray tube
    heat unit = kVp x mAs x w (waveform factor)
57
Q

define waveform factor

A
  • different forms of current
  • large number of pulses = high quality x-rays and more heat
58
Q

what’s the waveform for a single phase?

A

1

59
Q

whats the waveform for a three phase - six pulse

A

1.35

60
Q

whats the waveform for a three phase - twelve pulse

A

1.41

61
Q

whats the waveform for high frequency

A

1.45

62
Q

define tube rating

A
  • maximum allowable exposure factors (mA and kVp) without overheating the tube
  • included in all x-ray tubes
  • kilowatts (kW) per 0.1 seconds
  • varies on manufacturer
63
Q

name the tube loading factors

A
  • exposure time
  • filament size
  • anode angle
  • anode rotation speed
64
Q

true or false: modern x-ray tube notify users when the tube is overheating

A

true

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