Factors controlling the X-ray beam intensity Flashcards
(42 cards)
What is the intensity of the beam mean?
Total amount of energy contained in the x-ray beam
What does the quantity mean?
Number of photons in the beam. Primarily related to tube current and exposure time
What is the equation for intensity?
Intensity: Quantity X Quality
What is quantity expressed as?
tube current (mA) X time (sec) → mAs
What is quality?
Average energy the x-ray beam
What is quality of beam controlled by?
tube voltage (kVp)
What is quantity of beam controlled by?
tube current and exposure
time
X-ray of beam is heterogeneous or homogeneous?
heterogeneous
What are the factors that control x-ray beam intensity?
- Tube voltage
- Exposure time
- Tube current
- Filtration
- Collimation
- Source-receptor distance
As the tube voltage increases what happens to the…
Number of photons
Mean energy
Maximum energy
o Number of photons generated increases
o Mean energy of photons increases
o Maximum energy of photons increases
As tube voltage increases the beams become more or less efficient?
more
As the exposure time increases what happens to the…
Number of photons
Mean energy
Maximum energy
o Number of photons generated increases
o Mean energy of photons is unchanged
o Maximum energy of photons is unchanged
As the tube current (mA) increases what happens to the…
Number of photons
Mean energy
Maximum energy
o Number of photons generated increases
o Mean energy of photons is unchanged
o Maximum energy of photons is unchanged
If double the mA you must _____ the time to have the same energy/number of photons
half
What does filtration do?
Selectively removes long wavelength (low energy) x-rays
What are the inherent filtrations in the x-ray machine?
o Glass envelope
o Immersion oil
o Metal housing
o Tube window
What are the added filtrations in the x-ray machine?
aluminum disks
As the filtration increases what happens to the…
Number of photons
Mean energy
Maximum energy
o Number of photons decreases
o Mean energy of photons increases
o Maximum energy of photons is unchanged
What does collimation do?
Restricts the size and shape of the beam.
Adding a collimator does what to the…
Number of photons
Mean energy
Maximum energy
o Number of photons decreases
o Mean energy of photons is unchanged
o Maximum energy of photons is unchanged
What is the inverse square law for the source-to-receptor distance?
Intensity of the beam varies inversely to the square of the source-to-receptor distance.
What does the inverse square law say if the distance is doubled the intensity will be…
1/4
What does the inverse square law say if the distance is tripled the intensity will be…
1/9
What does the inverse square law say if the distance is halved the intensity will be…
4x
