Chapter 6 Flashcards
What does mA control?
Size of the filament, focal spot size, size of the beam, and the resistance
How does mA effect resistance?
The higher the mA, the bigger the electron beam, the less the resistance
What is saturation current?
Filament is heated with mA and there is no more electrons to boil off
What is Thermionic Emission?
Electrons boil off
Where do electrons hang out after boiling off the filament?
Space charge
What charge does the focusing cup have?
Negative
What causes the electrons to move from the cathode to anode?
kVp
Electric potential
Potential difference
What charge does the Anode have?
Positive
Where are Xrays and heat made?
The focal spot
What are the 2 interactions within the tube?
Characteristic
Brems
When does a Charactertistic interaction happen?
When incoming electron is at least 69.5 keV
If kVp is less than 70, then all photons will be:
Brems
What happens during a Brem’s interaction
Filament electron misses tungsten electrons and gets attracted to the nucleus
The stronger the attraction, the more energy the filament loses when it breaks and the stronger the brems photon
What is the average energy of Brems?
1/3 of the kVp selected
What is the beam before filtration?
Heterogenous
What is the beam after filtration?
Homongenous
What does total filtration need to be a minimum off?
2.5mm of Al
Why do we use filtration?
To take out any weak photon that would only contribue to patient dose, they are undiagnostic
How much Al is inherent filtration?
.5mm
What is total filtration?
Inherent + added
What is Beam hardening?
Filtration takes away weak photons and increases the overall average energy of the beam
What are compensation filters?
Used to compensate for vatiations in patient thickness and will create a more uniform exposure
How should a wedge filter be used?
Thick part of wedge over thin part of patient
What is HVL?
Amount of Al necessary to reduce the beam to 1/2 its intensity
What is the normal HVL?
3-5mm Al
How does HVL effect beam quality and quantity?
Increases quality
Decreases quantity
What is beam quantity?
The number of x-rays in a beam
What is beam quantity affected by?
mAs
kVp
Distance
Filtration
Grid
How does beam quantity affect radiation dose to the patient?
An increase in quantity, increases the radiation dose
What type of relationship does mAs have with beam quantity?
Direct
How does a 15% change in kVp affect quantity of Xrays?
Halving or doubling the quantity of xrays reaching the IR
What is the main control to change quantity?
mAs
How does beam quantity vary with distance?
Intensity of the beam gets less over large distances (inverse square law)
How does distance affect divergence?
As distance increase, beam divergence decreases
What is beam quality?
Strength or penetrating ability of the photons transmitted through the body
What color is created when then photons reach the IR?
Black
What color is created when the photons don’t reach the IR?
White
What is the relationship between kVp and quality?
The higher the kVp, the higher the quality of the beam
Other names for beam quantity?
Patient dose
Rate
Amount
Number
Quantity
How does SID affect beam divergence?
The greater the SID, the less the beam divergence
How does FSS affect beam divergence?
The greater the FSS, the greater the beam divergence
How does collimation affect beam divergence?
The greater the collimation, the less the beam divergence
