X-ray Tube Construction Flashcards
Milliampere (mA) and Time (s) controls?
Quantity and Density
How does Milliampere (mA) control quantity?
Amount of electrons emitted at the filament by process of thermionic emission
- more # of electrons = more # of x-rays being emitted
- less # of electrons=less # of x-rays being emitted
How does Time (s) control quantity?
determines length of time electrons are allowed to flow from cathode to anode
- more time -> more electrons> more x-ray
- less time-> less electrons-> less x-ray
The combination of Milliampere (mA) and Time (s) is?
mAs (milliampere seconds)
-treated as one unit
Kilovoltage (kV) controls?
- Quality
- Penetrating power
- Energy
- Density and Contrast
What is Contrast?
difference b/w black and white
ex)
- The higher the kV the darker the image
-The lower the kV the lighter the image
What is Density?
Overall degree of darkness
ex)
- too strong of kV the blacker the image will get
-too light of kV the whiter the image
There are three different types of External and Mechanical Support in a X-ray Room Structure. What are they?
- Ceiling
- Floor-to Ceiling
- C arm
Ceiling support
- most common
- freely moves in all directions : transverse
Floor-to- Ceiling support
- Multi-directional
- Requires effort to move
C arm Support
- Nearly limitless in tube position
- Robotic and fluid in motion
- Angiography
Protective Housing is considered to be_____?
Isotropic
The useful beam-emitted through the window of protective housing is also called?
Primary beam
Anything else which escapes the protective housing is called?
Leakage radiation or Secondary beam
-non-diagnostic
- unnecessary exposure to both patient and technologist
Protective housing is lined with what material?
Lead
Why is protective housing lined with lead? and why is protective housing important?
- reduce leakage radiation (<100 mR/hr @1meter)
2.
-Provides mechanical support
- Protects from damage caused by rough handling
Protective housing contains ________ to insulate from shock and dissipate heat.
Oil
Electron to x-ray efficiency is __%
1%
-99% is heat
What is Pyrex glass and why is it important?
- withstands large amounts of heat
- Vacuum
- more efficient x-ray production
- Longer tube life
What is a Cathode ?
Negative Electrode Filament
-(2) coils of wire (toaster vs x-ray filament)
What is Dual Focus?
Refers to Large FSS and Small FSS
What does FSS stand for?
Focal Spot Size
Dual Focus Cathode contains 2 filaments. What are they?
- Small Filament
- Large Filament
Small focal spot size filament uses ____mA or less
200
-provides better detail
- best for small body parts
Large focal spot size filament uses _____mA or more
300
-larger body parts
-can withstand more heat
What is a Focusing Cup?
Negative charge that surrounds the filament on the cathode
-confines electron beam to small area of anode
What is Thermionic Emission?
When electrons are boiled off
What is the space-charge effect?
Prevents subsequent electrons from being boiled off due to electrostatic repulsion (same charges repel)-Coulomb’s Law
What is an Anode?
Positive electron
What is a stationary Anode?
- High tube current and power not required
- Used in dental offices, clinics, portables, simple x-ray units
- Has a copper Anode and Tungsten Target
What is a Tungsten Target?
- In the middle of copper anode
- Most important primary material
What is a con to a stationary anode?
Pitting can occur
What is Pitting?
wear and tear of the Tungsten Target which can also lead to tube failure
What does a Rotating Anode help do?
x-ray tubes capable of producing high-intensity x-ray beams in shorter time periods
-Has Copper, Molybdenum, Rotating Tungsten Target, Target Track
The rotating anode has________ to ________ RPM?
3,600 to 10,000 RPM (Rotations Per Minute)
Why is a Rotating Anode better compared to a Stationary Anode?
- Better for heat dissipation
- Higher tube currents with shorter exposure time (more efficient)
- Increased heat loading abilities
What is a Target (track)?
Area of disc that the electrons strike, and are converted into x-rays
Disc is composed of 3 layers. What are they?
- Tungsten/rhenium
- Molybdenum
- Graphite
Why is Tungsten used?
- High atomic #(74)
- Higher Efficiency
- Thermal Conductivity
- Better at heat dissipation
- High Melting Point
- Minimize occurences of pitting
What is the high melting point of Tungsten?
3410 °C (6170 °F)
