Final Review (history and xray tube) Flashcards
Who were xrays discovered by?
Wilhelm Conrad
When were xrays discovered?
November 8, 1895
What was the first xray?
Roentgens wife’s hand
Who was the first fatality from xrays?
Clarence Dally
Who won the first Nobel prize presented for physics in 1901?
Roentgen
Who devised a fluoroscope using a fluorescing screen
Thomas Edison
Who improved crookes tube?
William Coolidge
what are the 3 Cardinal Rules of Radiation Protection?
Time, Distance, Shielding
What was designed in order to prevent radiation injury and effects?
-Cardinal Rules (time, distance, shielding)
-lead protective apparel worn by all radiation workers
-Radiation dose monitored through the use of a dosimeter
Four things that are needed for the production of xrays?
-Source of electrons (cathode filament)
- Target (tungsten anode)
-High voltage
-vacuum
A form of electromagnetic radiation
Xrays as energy
Behave both like waves and like particles
Xrays as energy
Move in waves that have wavelength and frequency
Xrays as energy
Wavelength and frequency are inversely related
Xrays as energy
Xrays also behave like particles and move as photons
Xrays as energy
What are some properties of xrays?
-xrays are invisible
-xrays are electrically neutral
-Xrays have no mass
-Xrays travel at the speed of light in a vacuum
-Xrays cannot be optically focused
-Xrays form a polyenergetic or heterogeneous beam
-Xrays can be produced in a range of energies
-Xrays travel in straight lines
- Xrays can cause some substances to fluoresce
-Xrays cause chemical changes to occur in radiographic and photographic film
-Xrays can penetrate the human body
-Xrays can be absorbed or scattered by tissues in the human body
- Xrays can produce secondary radiation
-Xrays can cause chemical and biologic damage to living tissue
Xray prodcution
-The production of xrays require a rapidly moving stream of electrons that are suddenly decelerated or stopped.
-The negative
electrode (cathode) is
heated, and electrons
bare emitted
(thermionic emission)
- The electrons are
attracted to the anode,
move rapidly towards
the positive electrode
and are stopped or
decelerated.
Protects against leakage radiation and electric shock
Tube housing
-metal or glass envelope
-negatively charged electrode
-positively charged electrode
Xray tube housing
What is part of the cathode?
Filament and focusing cup
Cathode assembly
Filament (coiled tungsten wire helix)
Focusing cup
associated wiring
low voltage side of xray circuit
Source of electrons
What types of coiled tungsten wire is there?
wire filament for large and small focal spot
What charge is the cathode?
Negative
What charge is the anode?
Positive
What kind of material is the filament made of?
Thoriated tungsten
What material is the focusing cup made of?
Nickel
May also be called the focal point, focal spot or the focal track?
Target
The process of boiling off electrons and produces a cloud of electrons by heating the filament
Thermionic emission
Dangers of Radiation
-Never stand in primary beam
-Collimating as small as you can
-Never hold patient
-Females 11-50 always shield
Occurs when no more electrons can be boiled off of the filament
Space charge effect
Is the primary thermal conductor of the tube
Anode
Three components of the anode
Anode, stator, and rotor
Why is tungsten used?
High melting point and difficult to vaporize
What are the two types of anods
Rotating and stationary
portion of the anode struck by the electrons
Target
What is the anode made up of
Tungsten Rhenium Alloys
What does it mean to have two filaments?
Dual Focus tube
Why does the xray tube need to be warmed up?
To prevent cracking and maintain vacuum
Purpose of rotating anode
promote greater heat dissipation
-Decelerates and stops electrons
-energy converted to heat and xrays
-Brems and characteristic interactions
Target
What does a rotating anode require?
-requires a stator and rotor to rotate
-tungsten metal
What determines the number of electrons boiled off
mA
Atomic number of tungsten rhenium alloy
74
Absorption of xrays produces in the tube by the anode, causes uneven distribution of xray intensity between the cathode and anode, more intensity of cathode side (fat cat)
Anode heel effect
Area where electrons strike the anode
Focal Spot
Leakage radiation Limit
100 milliroentgens per hour at 1 meter
Physical area of the focal track being hit by the electrons
Actual focal spot
What is the environment inside the xray tube once all air has been removed
Vacuum
Tube failure
-Tube arcing (vaporized tungsten collection on envelope)
-filament breakage (“boost” and hold)
-Filament heated
-causes electrons to be released from filament
-similar to filament heating in an incandescent lightbulb
-cathode filament is in a low temperature, pre-heat mode until xray exposure is initiated
Thermionic Emission
Xray tube efficiency
1% xray
99%heat
is housed in focusing cup and produces electrons to produce image
filament
Three functions of the anode:
-Target surface for xray production
-Conducts high voltage
-serves as primary thermal conductor
What changes the charge of the focusing cup from negative to positive
Grid Biased Tubes
Necessary qualities of the anode
High atomic number
high melting point
high heat conduction ability
Heat tolerant pyrex glass or metal
Envelope
What do the electrons become when they hit the anode
photons
What two things control the size of the effective focal spot
Size of the focal spot and anode target angle
-assists with heat loading
-backed with molybdenum and/or graphite
-backing acts as “heat sink”
-Increases xray tube thermal capacity
Anode layering
-space charge effect
-compresses thermionic cloud
-concentrate the electron beam towards the focal spot of the anode
Focusing cup
What is the anode made up of?
Tungsten rhenium alloy
-made of molybdenum
-connects the anode to the rotor
Stem
What is the line focus principle
Spreads heat over a greater area of the anode and allows the effective focal spot to be smaller than the actual focal spot
What is the purpose of the glass envelop
Absorbs xrays and ensures a vacuum
Purpose of the focusing cup
To group the electrons for their passage to the anode
Why do we follow the warm up procedure?
To prevent the tube from cracking and to maintain vacuum
A molybdenum shaft is used to connect the anode to the rotor because
It is a less dense metal with a high melting point that helps anode to spin faster
What does “pitting” mean
Holes on the focal track
Portion of anode that electron stream contacts
Target Area
Purpose of the fan in the tube housing is to
Promote heat dissipations
Average anode rotation speeds in diagnostic ray tubes are in the ranges of:
3,000-10,000
The only thing located outside of the envelope that consists of copper windings
Stator
Made of a copper cylinder in the step of the xray tube and is supported by the high strength ball bearings
Rotor
What does the protective housing consist of ?
Metallic
supports xray tube
controls leakage and scatter radiation
prove mechanisms to cool tube
How can we extend the life of the tube
-tube warm up
-avoid frequent “boosting”
-use low mA when possible
-use low speed rotation when possible
-follow rotating charts
-avoid rough handling
-listen to unusual sounds
What is off focus radiation
Undesirable part of the beam, not hitting anode, low energy and no diagnostic value, produces “ghosting”
What does xray stand for
the X in xray means unknown
What is the divergence of the beam
Energy that is coming out and whats interacting with the patient
Compare and contrast actual focal spot and effective focal spot
Actual focal spot is the area being hit by electrons and effective focal spot is projected area of xray beam.
Effective focal spot should be smaller.
A before E
results in suboptimum anode rotation speed
stator failure
True or False
Xrays are invisible
true
True or false
Xrays can travel around corners
False
Sequence of taking xrays
- Current runs through the filament circuit
- Filament gets hot
- Filament glows
- Filament boils of electrons
- Electrons form a space cloud
- Electrons are repelled from the focusing cup
- Electrons are attracted by the anode
- Electrons move over to the anode
- Electrons slam into the anode at the target
- Electrons lose energy
- Light, heat and X-rays are produced
- Focal spot is formed
- X-rays are emitted isotropically
- X-rays are absorbed by the glass and metal housing
What helps the stator to rotate properly
Ballbearings
-Ferromagnetic bars arranged in cylindrical pattern
-inside xray tube glass envelope
-copper cylinder connected to anode disk by molybdenum stem
-turns when stator is energized
Rotor
what type of body parts would the large filament focus on
large focusing body parts (more heat)
what does the filament length and width impact
recorded detail or special resolution
Typically controlled by the xray circuitry and wont go higher than what is already set
Saturation Current
-Heat tolerant pyrex glass or metal
-Two functions: supports anode/cathode assemblies and maintain a vacuum
-modern tubes now metal
Envelope
Near perfect and critical to efficient xray productions
vacuum
Protective housing provides mechanisms to cool tube
-cooling oil surrounding tube
-cooling fans
-water cooling in high end tube designs
-metallic
-supports xray tube
-controls leakage and scatter radiation(lead lined)
-provides mechanisms to cool tube
Protective housing
Be able to label xray tube
