Chapter 5 Flashcards
What is general tube construction?
- lead lining
- oil bath
- cooling fans
- electrical insulation
- large cables
- absorbs stray photons
Why would a tube housing get hot?
With continuous use
X-ray tubes act as a what?
As an electronic vacuum
What does an x-ray tube consist of?
- anode
- cathode
- induction motor
- encased in a glass or metal enclosure
What is a glass envelope made up of?
Generally made of borosilicate glass because its heat resistant
What is a metal envelope made up of?
Strong metal like copper or steel, it provides constant electrical potential
What is the positive side of an x-ray tube?
Anode
Anodes provide a _____ for electrons to produce x-rays.
A target
An anode serves as?…
An electrical and thermal conductor
What are 2 types of anode?
- stationary anode
- rotating anode
Stationary anode is made up of?
It’s a tungsten button embedded in a copper rod
What is the advantage and disadvantage of a stationary anode?
Advantage:
Disadvantage: rapidly building heat can damage the tube which limits use
Rotating anode is made up of?
Rotating tungsten-coated molybdenum disc mounted on a copper shaft with a molybdenum core
What is the advantage and disadvantage of a rotating anode?
Advantage: spreads heat produced during x-ray production over a larger surface area
Disadvantage:
Copper is used a part of ?…
Is part of the shaft because it has excellent thermal and electrical conductive properties
Molybdenum is part of?…
Is used as a disc base & core because it has a low thermal conductivity and it is a light but strong alloy
Tungsten is used for?
It’s used because it has a very high melting point and a high atomic # (74), improving the efficiency of x-ray production
What is rhenium used for?…
It can be added to the tungsten to increase thermal capacity and tensil strength
What does an induction motor consist of and do?
Consist of : stator and rotor
It allows the rotation of the anode in a vacuum without engineering a motor into the vacuum
What is a stator?
Is made up of electromagnet arranged in pairs around the rotor
What is the rotor?
an iron core surrounded by coils.
What is the line focus principle?
A large actual focal spot size can be maintained and a small effective focal spot size can be created
Target face less than 45 degrees is ?…
An effective focal spot will be smaller than the actual
Target angles 7 to 18 degrees are?…
Are for a general purpose tube (12 degrees is the most common)
The smaller the effective focal spot, the?…
The sharper the image will be
What is the anode heel affect?
Decreases the intensity of the x-ray beam to be less because it is absorbed in the target heel
What does a cathode do?
It provides the source of the electrons needed for x-ray production
Where is the cathode located?
It’s the negative end of the tube
What is the dual focus tubes?
General purpose tubes with two filaments
What is a focusing cup made up of?
Nickel and surrounding the filaments back and sides
What shortens an x-rays tube life?
- frequent high or maximum exposure factors
- low but longer exposure factors
- overloading the Filament
what are the 3 processes of heat transfer?
- Conduction of heat by tolerant materials
- Radiation of heat energy from anode to oil bath
- Convection of heat into the room by cooling fans
Heat units are a measure of what?
a measure of the amount of heat stored in a particular device
how to calculate heat units?
kVp * mA * s * c
If there are multiple exposures, the formula is multiplied by the # of exposures
how do you extend x-ray tube life?
- warm up machine
- do not prep the rotor exclusively
- do not routinely use extremes of exposure factors
