LRA-222 Week 1 Tube Components Flashcards
what specialties in radiology uses x-rays?
- radiography
- fluoroscopy
- mammography
- computed tomography
define thermionic emissions
- boiling off electrons
- heating up the filaments (that’s housed in the focusing cup) and creating a cloud of electrons
define cathode
- where electrons are located
- negatively charged
define anode
- positively charged
- absorbs electrons and creates x-rays
define glass envelope
- creates an air free vacuum around the anode and cathode
- made up of borosilicate glass
- protects tube from oxidation and corrosion
tube/metal housing
- 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
define space charge
- cloud of electrons
define space charge effect
- at 1,000 mA, no more electrons can be forced out of the filament
define dual focus
- 2 cathode filaments
- small filament
- large filament
how many filaments are in the cathode?
- two
- small and large filament
name the factors of a small filament
- used for small mA
- has a small heat capacity
- small body parts
- used for small body parts
- high spatial resolution
name the factors of a large filament
- low spatial resolution
- large mA
- used for large body parts
- large exposures
where are the filaments located?
- both filaments are housed in the focusing cup
define focusing cup
- to focus the electron beams (so they go in a straight line)
- narrow electron beam = increase in spatial resolution
how does the focusing cup keep a narrow electron stream?
- the focusing cup is also negatively charged
- because of the charge, they repel the electrons that are produced, resulting in a narrow stream
what are the 2 types of anodes?
- stationary anode
- rotating anode
define stationary anode
- 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
define rotating anode
- rotating disk
- electrons hit multiple spots (large surface area)
- increases heat capacity
- complex design
- high heat capacity
- high exposures
why are stationary anodes not ideal in general radiography?
- because the electrons only hit one spot, it easily damages the anode, resulting in a short duration
define induction motor
- turns the another without contacting the actual anode
what are the different parts of the induction motor?
- stator
- rotor
- bearing
define stator
- uses electromagnets
- activated in series to induce turning of the rotor
define rotor
- attached directly to the anode
- rotates
define bearings
- in between the rotor
- low friction spheres that allow for free rotation of the rotor
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
what are the angles in an anode angle?
- anode angle ranges from 6 to 20 degrees
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
what happens when the anode angle decreases?
- increases anode hell effect
- decreases intensity
when anode angle decreases -
anode hell effect increases
when SID decreases -
- anode heel effect increases
when field size increases -
- anode heel effect increases
define actual focal spot
- physical area of the anode where electrons concert into x-rays
- electron stream
- where heat is created
define line focus principle
- relationship between actual focal spot and effective focal spot (in the anode)
- affects heat capacity, spatial resolution, and beam coverage
define why is a large focal spot desired?
- helps spread out the heat
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
when we have a small effective focal spot it-
decreases penumbra and increases spatial resolution
when we have a large effective focal spot it-
increases penumbra and decreases spatial resolution
what is the desired goal with the focal spots?
- we want a large focal spot with a small effective focal spot
when positioning a patient, where should the least dense body part be placed?
- least dense portion should be placed on the anode side
with a large actual focal spot, heat capacity -
- increases
with a small effective focal spot, spatial resolution -
- increases
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
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)
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”
true or false: off focus can interfere with processing the digital image
true
how does off focus radiation affect patient dose?
- patient dose increases because it captures parts outside of the collimated area
with an off focus principle, it -
- increases patient dose
- decreases spatial resolution
- decreases contrast
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
how does off focus radiation impact an image?
- disturbs the brightness and contrast of the image, making it harder to interpret
how can we fix off focus radiation?
shuttering
define shuttering
- “cutting” off the bright portion of the collimation
- known as “post processing collimation”
when should post processing collimation be used?
- only to remove the visibility of large regions of brightness
true or false: never use post processing radiation to eliminate anatomical information
true
define tube loading
- heat created within the x-ray tube (especially at the anode)
what happens if the x-ray tube is overheated or overloaded?
- it can cause the anode to melt or rupture the x-ray tube
define heat units
- heat created within the x-ray tube
heat unit = kVp x mAs x w (waveform factor)
define waveform factor
- different forms of current
- large number of pulses = high quality x-rays and more heat
what’s the waveform for a single phase?
1
whats the waveform for a three phase - six pulse
1.35
whats the waveform for a three phase - twelve pulse
1.41
whats the waveform for high frequency
1.45
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
name the tube loading factors
- exposure time
- filament size
- anode angle
- anode rotation speed
true or false: modern x-ray tube notify users when the tube is overheating
true
