6. The X-ray Tube (P2) Flashcards
What prime factor controls the limits of the focusing cup?
mA
What is the role of focusing cups?
To focus the electrons produced by the tungsten filament coils to the focal spot
What are some characteristics of the focusing cup? ei; materials, conductivity, charge, thermal energy
- Made of nickel
- Conductor
- Negatively charged
- Not a good thermionic emitter (not going to release its own e-)
Why is it important that the filaments are a good thermionic emitter?
Because the filaments are responsible for producing the electrons by heating the coil to energize and release them
What are the pros and cons of a larger focal spot?
Pros: Larger mA, better heat dissapation
Cons: Lower resolution (focal spot blooming), decreased SR
What type of relationship does mA and the filaments have?
A direct relationship
What does increasing the kVp do to the photons?
Increases their energy
What are the 3 functions of the anode?
- Supports the target
- Conducts current
- Dissipates heat
With a stationary anode would you need a higher or lower mA and kVp? Why?
Lower, because you are localized to one area
What is the unit for tungsten? What is its atomic number?
W…yes, just W….nothing else
Atomic #: 74
Does tungsten have a high or low binding energy? Why?
It has a high binding energy which is because it causes high energy to be released
which means its inner shell electrons are tightly bound to the nucleus, requiring a large amount of energy to remove them, resulting in high energy X-ray photons when they are ejected and subsequently replaced by electrons from higher energy levels
What is the stem made out of in a stationary anode?
Copper
What are 4 characteristics that a stationary anode has?
- High conductivity
- Low melting point
- Tungsten Target
What is the atomic number of tungsten?
74
What are 3 characteristics of tungsten?
- High melting point
- High thermal conductivity
- Low vaporization
What is unequal thermal expansion and contraction called?
Pitting
What are the 3 tube ratings?
- mA
- Time
- kVp
What are the 5 parts of the spinning anode?
- Disc
2. Focal track
3. Stem
4. Rotor=inside
5. Stator=outside
What makes up the focal track?
Focal spot + rotation
Why is a spinning anode better in terms of heat?
It allows for better heat dissipation (Looses heat when its spinning so it doesn’t get hot)
What material is the spinning anode made of?
- Made of Tungsten and 10% Rhenium
What are the layers of behind the tungsten?
- Molybdenum
- Carbon (graphite)
What is the stem in a spinning anode and what is it made of?
It connects disc to rotator, is thin and made of molybdenum
What is the rotor and what is it made of?
-Rotates on bearings
-High conductivity
-Made of copper
How fast does the anode rotate?
> 3000rpm up to 12000
What is the function of the stator and what is it made of?
-Causes rotor to spin, but is stationary itself
- Is an Induction motor
-Keeps alternating where the current runs through
-Current that is created in the copper is the same polarity of what is in the coil
What 4 parts of the tube are most likely to wear down?
- Filament-space charge created here
- Anode
- Bearings-helps our disc spin
- Housing wear
What is filament wear caused by?
-High mA
-Longer prep-when your holding halfway (building space charge and rotate anode)
What is anode wear caused by?
- Uneven thermal expansion
- High exposure ratings
What is bearing wear caused by?
-Heavy use (higher techniques)
-Longer prep
What is housing wear caused by?
-Physical Damage
-Overheating
What are the consequences of filament wear?
-Tungsten plating on tube-tungsten vaporizing (builds up metallic substance on tube)
-Arcing- attracts electricity to the tungsten plating
-The filament may break due to arcing over time
What are the consequences of anode wear?
Pitting=Unequal x ray intensity
What are the consequences of bearing wear?
- Slower rotation
- More pitting
- Grinding noise
What are the consequences of housing wear?
Oil leakage=leads to more heat
What are 3 ways to prevent tube wear?
- Lower techniques
- Shorter preps
- Tube warm up-prevents cracking the target
- Helps prevent anode damage
What is the purpose of the rating charts? Why is there two?
-Shows safe and unsafe combinations of kVp and mA
-2 charts for the two different focal spots, for different phase generators, rotation speed
What are the 6 factors that affect tube rating?
- FS size
- Rotation speed
- Disk Diameter
- Waveform
- Segmented/Grooved anode-gives room for expansion
- Metal tube-can control the potential of the tube
What is heat storage capacity?
How many exposures you can do without cooling
(Refers to the bearings)
What are the consequences of composition?
-Differing expansion
-Differing conduction
-Damage to the bearings
What does it mean by heat units/second
-Amount of e- emitted and hitting the target per second
(refers to filament and target)
What are anode cooling charts?
-Shows heat capacity of anode and length of time to completely cool after its received a certain amount of heat
-Only one chart per machine
