Tube Flashcards
Helps with leakage radiation and shock from the tube; metal lined
Protective housing
What type of tubes do we use now?
Coolidge tubes
Proper housing measurement
100 mR(milliroetgen)/hr at 1 meter
When x-rays are produced, how are they emitted?
Isotropically
What is used in x-ray tubes that serves as an electrical insulator and a thermal cushion?
Oil
Vacuum tube to withstand large amount of heat
Glass envelope
These are used in place of glass envelopes
Metal envelope
Is needed to provide efficient x-ray production
Vacuum
Why is a vacuum essential for efficient x-ray production?
The removal of air permits electrons to flow from cathode to anode without encountering the gas atoms of air
What is the number one reason for tube failure?
Gassy tube
Negative side of the tube
Cathode
What are the two main parts of the cathode?
Filament
Focusing cup
What is the filament made out of?
Thoriated Tungston
Why is thorium added to the filament?
To increase thermionic emission
Electron buildup when you’re about to send the electrons from the cathode to the anode
Space cloud
Boils electrons off filaments; separation of electrons
Thermionic emission
When do you use a smaller filament?
When you use smaller mA
When do you use a larger filament?
When you use a larger mA
Focuses the electrons to the area in the anode
Focusing cup
Negatively charged so it works on the principle of electrostatic repulsion
Focusing cup
What is a tube called with two electrodes?
Why?
Diode
Because it has a positive and a negative side
Positive side of the x-ray tube
Anode
Target area that is struck by electrons
Anode
What material is the anode made of?
Tungsten
What is the function of the anode?
Electrical conductor; Where x-rays are created
What are the two types of anodes?
Stationary
Rotating
Used in dental and portable machines; aren’t seen very often
Stationary anodes
A lot more productive than the stationary anode
Rotating anode
This type of anode helps dissipate heat and doesn’t wear down as fast
Rotating anode
What is the target angle range of the rotating anode?
5°-20°
Why would you want a larger diameter rotating anode?
Increases workload
What is the range for the speed of rotation for the rotating anode?
3,400 - 10,000 RPMs
What is the speed for a single-phase rotating anode?
3-phase?
What type of frequencies do they each put off?
3,400; low frequency
10,000; high frequency
How does the rotating anode rotate?
Electromagnetic induction
What are the two parts of the rotating anode?
Stator
Rotor
Outside of the glass envelope; Consists of a series of electromagnets
Stator
Inside of glass envelope; is a shaft made of bars of copper and soft iron
Rotor
Why is it important to warm up the anode?
Because if you don’t, the anode can crack
Angling of the target in the anode
Line-Focus Principle
What are the perks to having an angled target?
Gives a larger actual focal spot size and a smaller effective spot size; Helps dissipate heat while creating better detail
Which FSS hits the anode?
Actual FSS
Which FSS hits the patient?
Effective FSS
When is the actual FSS larger than the effective FSS?
Always, no matter what the angle is
What is the range for effective FSS?
0.6-1.2
If you use the larger filament, is your FSS smaller or bigger?
Larger
If you use the smaller filament, is your FSS smaller or bigger?
Smaller
If you lower your target angle, what does it do to the effective FSS?
What happens to your heat load?
Gets smaller
Increases
If you increase your target angle, what happens to your heat load capacity?
Increases
What is the disadvantage of using the line-focus principle?
Heel Effect
What is the heel effect?
The radiation intensity on the cathode side of the x-ray field is higher; the intensity on the anode side of the x-rayed field is lower
Composed of photons that were not produced at the focal spot
Off-focus radiation
3 Devices used to reduce scatter
Beam Restrictors
Grids
OID
What is the formula to calculate the cooling chart for a single phase heat unit?
3-phase?
kVp x mA x time
kVp x mA x time x 1.40
What type of current is the filament current?
Alternating current
