LRA-222 Week 1 Tube Components Flashcards
(64 cards)
1
Q
what specialties in radiology uses x-rays?
A
- radiography
- fluoroscopy
- mammography
- computed tomography
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
3
Q
define cathode
A
- where electrons are located
- negatively charged
4
Q
define anode
A
- positively charged
- absorbs electrons and creates x-rays
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
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
7
Q
define space charge
A
- cloud of electrons
8
Q
define space charge effect
A
- at 1,000 mA, no more electrons can be forced out of the filament
9
Q
define dual focus
A
- 2 cathode filaments
- small filament
- large filament
10
Q
how many filaments are in the cathode?
A
- two
- small and large filament
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
12
Q
name the factors of a large filament
A
- low spatial resolution
- large mA
- used for large body parts
- large exposures
13
Q
where are the filaments located?
A
- both filaments are housed in the focusing cup
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
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
16
Q
what are the 2 types of anodes?
A
- stationary anode
- rotating anode
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
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
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
20
Q
define induction motor
A
- turns the another without contacting the actual anode
21
Q
what are the different parts of the induction motor?
A
- stator
- rotor
- bearing
22
Q
define stator
A
- uses electromagnets
- activated in series to induce turning of the rotor
23
Q
define rotor
A
- attached directly to the anode
- rotates
24
Q
define bearings
A
- in between the rotor
- low friction spheres that allow for free rotation of the rotor
25
define the anode heel effect
- phenomenon that effects the intensity of the x-ray beam
- anode side of the tube will be weaker than the cathode side
26
what are the angles in an anode angle?
- anode angle ranges from 6 to 20 degrees
27
how does the angle of the anode affect the heel effect?
- 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
what happens when the anode angle decreases?
- increases anode hell effect
- decreases intensity
29
when anode angle decreases -
anode hell effect increases
30
when SID decreases -
- anode heel effect increases
31
when field size increases -
- anode heel effect increases
32
define actual focal spot
- physical area of the anode where electrons concert into x-rays
- electron stream
- where heat is created
33
define line focus principle
- relationship between actual focal spot and effective focal spot (in the anode)
- affects heat capacity, spatial resolution, and beam coverage
34
define why is a large focal spot desired?
- helps spread out the heat
35
define effective focal spot
- 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
when we have a small effective focal spot it-
decreases penumbra and increases spatial resolution
37
when we have a large effective focal spot it-
increases penumbra and decreases spatial resolution
38
what is the desired goal with the focal spots?
- we want a large focal spot with a small effective focal spot
39
when positioning a patient, where should the least dense body part be placed?
- least dense portion should be placed on the anode side
40
with a large actual focal spot, heat capacity -
- increases
41
with a small effective focal spot, spatial resolution -
- increases
42
what are the factors of a small anode angle?
- 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
what are the factors of a large anode angle?
- 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
define off focus radiation
- 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
true or false: off focus can interfere with processing the digital image
true
46
how does off focus radiation affect patient dose?
- patient dose increases because it captures parts outside of the collimated area
47
with an off focus principle, it -
- increases patient dose
- decreases spatial resolution
- decreases contrast
48
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
true
49
how does off focus radiation impact an image?
- disturbs the brightness and contrast of the image, making it harder to interpret
50
how can we fix off focus radiation?
shuttering
51
define shuttering
- "cutting" off the bright portion of the collimation
- known as "post processing collimation"
52
when should post processing collimation be used?
- only to remove the visibility of large regions of brightness
53
true or false: never use post processing radiation to eliminate anatomical information
true
54
define tube loading
- heat created within the x-ray tube (especially at the anode)
55
what happens if the x-ray tube is overheated or overloaded?
- it can cause the anode to melt or rupture the x-ray tube
56
define heat units
- heat created within the x-ray tube
heat unit = kVp x mAs x w (waveform factor)
57
define waveform factor
- different forms of current
- large number of pulses = high quality x-rays and more heat
58
what's the waveform for a single phase?
1
59
whats the waveform for a three phase - six pulse
1.35
60
whats the waveform for a three phase - twelve pulse
1.41
61
whats the waveform for high frequency
1.45
62
define tube rating
- 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
name the tube loading factors
- exposure time
- filament size
- anode angle
- anode rotation speed
64
true or false: modern x-ray tube notify users when the tube is overheating
true
