Historical Perspective Flashcards
Dr. Roentgen used ____ to make the first x-ray
Crookes-Hittorf
Demonstration by crookes that cathode rays travel in straight lines
Cathode
Aluminum cross and anode
Fluorescent image
Dark shadow
There was no ____ so x-rays were emitted in ____ directions
Shielding
Direction
The ____ tube was a major advancement in tube design
Coolidge Hot cathode
It is a component of x-ray imaging system rarely seen by radiologic technologist
X-ray tube
Modern x-ray tube and coolidge tube is _____ tube
Vacuum tube
It contains 2 electrodes
Anode
Cathode
__ to __ cm long and __ cm in diameter
30 to 50 cm
20 cm
2 principal parts
Rotating (anode)
Cathode
Both anode and cathode are
Electrodes
Any tube that has two electrodes is called a
Diode
Self-rectification highest limits are about ___
30 mA at 90 kV
Overstepping these bounds can cause temperature rise in the anode target yo the point of
Thermionic emission
External parts of x-ray tube
Support structure
Protective housing
Glass or metal enclosure
Internal structures
Anode
Cathode
Three main methods of x-ray tube support
Ceiling support system
Floor to ceiling support system
C-arm support system
The most frequently used support system
Ceiling support system
Consist of two perpendicular sets of ceiling-mounted rails
Ceiling support system
This allows for longitudinal and transverse travel of x-ray tube
Ceiling support system
Had a single column with rollers at each end one attached to the ceiling mounted rail and the other attached to the floor mounted rail
Floor to ceiling support system
These system are ceiling-mounted and provide for very flexible x-ray tube positioning
C-arm support system
The tube is housed in a lead line metal
Protective housing
The x-ray photons are generated
Isotropically or in all directions
The housing is designed to ____
Limit the beam to window
The housing controls the ___ and __ , isolates the ___ and provides a means to ____ the tube
Leakage and scatter radiation
High voltage
Cool
Any photons that escape from the housing except at the port
Leakage radiation
Leakage radiation must not exceed ___ at ____
100 mR/hr at 1 meter
The ___ also provide mechanical support and protection from damage
Housing
The housing also contains ___ that provides more insulation and a thermal cushion
Oil
Some housing have ___ for cooling
Fan
The housing incorporates specially designed high voltage receptors to protect against ___
Electric shock
Glass enclosure is made of ___ to enable it to withstand the tremendous heat generated
Pyrex glass
The window is a ____ with thin section of glass where the useful bean is emitted
5 cm2
___ allows for more efficient production of x-ray and longer tube life
Vacuum
With the presence of air,
Electron flow from cathode is reduced
Fewer x-ray are produced
More heat are generated
Improvement in design incorporates metal rather than glass as part or all of the enclosure
Metal enclosure
___ tubes maintain a constant electric potential between the electrons of the tube current and the enclosure
Metal enclosure
They have longer life and less likely to fail
Metal enclosure
All high-capacity x-ray tubes now use ___
Metal enclosure
Cathode is negative side of the tube and contains two primary parts
Filaments
Focusing cup
Is a coil of wire with approx 2mm in diameter and 1-3 cm long
Filament
It emits electrons when heated
Filament
Filaments are made of __
Thoriated tungsten
Melting point of tungsten
3410*C
Add of 1-2% of ___ prolong tube life and efficiency of thermionic emession
Thorium
Most rotating anode x ray tubes have 2 filaments
Dual focus filament
Either filament can be used for lower mA station approx
300 mA or less
*dual focus filaments
Desposition on the inside of glass enclosure is the most common cause of tube failure
Tungsten vaporization
A shallow depression in the cathode assembly designed to house the filament
Focusing cup
It is a metal shroud that surrounds the filament
Focusing cup
The focusing cup has ___ charge
Negative
The effectiveness of focusing cup is determined by the ff:
Its size and shape
Its charge
Filament size and shape
Position of the filament in the focusing cup
X- ray tube current is adjusted by controlling the ___
Filament current
Emmision of electron from heated surface
Thermionic emission
Also known as thermal electron emission
Thermionic emission
Process by which charge carriers such are electrons or ions move over a surface by induction of heat
Thermionic emission
Formation of electron cloud near filament
Space charge
As kVp increases a greater percentage of thermionically emitted electrons are driven toward the anode
Saturation current
Thermionic emission at low kVp and high mA can be ___
Space charge
Consist of anode stator and rotor
Anode assembly
Positive aide of the tube
Anode
Functions of anode
Electrical conductor
Provides
Mechanical support
Thermal dissipator
Anode materials
Copper
Molybdenum
Graphite
It conducts electricity and radiates heat and contains the target
Anode
X ray tube classified by type of anode
Rotating
Stationary
Use in dental x ray imaging system, some portable imaging system w/ch high tube current and power are not required
Stationary anode x ray tube
The must be capable of producing high intensity x ray beams in short time
Rotating anode x ray tube
Allows the electron beam to interact with a much larger target area
Rotating anode
The heat is not confined to small area
Rotating anode
Construction of a rotating anonde
Base is made of ___ for a solid base
Target is made of ___
Parts of holding the target are made of ___
Graphite
Tungsten-rhenium alloy
Molybdenum
Area of anode stuck by the electrons from the cathode
Target
In rotating anode the entire rotating disc is the ___
Target
Target material
Stationary anode ___
Rotating anode ___
Tungsten alloy embedded in copper anode
Tungsten (W) with rhenium
High capacity tubes have ___ or ___ under the tungsten target thus making the anode lighter and easier to rotate
Molybdenum
Graphite
Reasons why tungsten is material of choice
Atomic number
Thermal conductivity
High melting point
Measure of the ability of substance to conduct heat
Thermal conductivity
Melting point of tungsten
3,422c or 6,192f
A form of extremely localize corrosion that leads to creation of small holes in the metal
Pitting corrosion
Actual target for stationary tube is 4mm2
Target area
Total target area of the rotating anode is 1,760 mm2
Target area
Most rotating anodes revolve at 3600 rpm
Rotating anode
Anode of high capacity tubes rotate at up to 10,000 rpm
Rotating anode
Shaft between the anode and the rotor
Anode stem
Sten is usually made of molybdenum because it is a poor heat conductor
Anode stem
