X-ray Beam Production 2 Flashcards
What is the energy level of a photon produced by a M–>K shell transformation?
Roughly 69.5 kEV. This transformation is known as K-beta
What is the energy level of a photon produced by a L–>K shell transformation?
Roughly 60 kEV. This is a K-alpha transformation?
In an intensity-photon energy graph, what are the two peaks seen?
These are K-alpha and beta characteristic radiation production. They occur at energies 60 and 69.5kV respectively.
What is the smooth curve seen on an intensity-photon energy graph?
This represents the x-ray photons generated via bremsstrahlung radiation.
What is the maximum energy of photon dictated by?
The max. photon energy is the same as the tube current. No photon can have more energy than that.
Why is there a lack of photons with low and high energy in an intensity-photon energy graph?
These photons are absorbed by the tissue and filters (within the tube). These regions are known as the low/high energy cut-offs.
Can you see M–>L or N–>M transition characteristic radiation on an intensity-photon energy graph?
No, because the photons produced via these transitions are so low-energy that they are absorbed by filters/the anode/tissue.
What happens to an intensity-photon energy graph if you decrease the tube current?
- Smaller area under the curve. Intensity is proportional to kEV squared, decrease in kEV means an exponential decrease in intensity.
- The line would tail-off at a lower photon energy (i.e. the tube current)
- Characteristic lines would move towards the left, but stay above their respective energy levels (60 and 69.5 kEV)
What happens to an intensity-photon energy graph if you increase the tube current?
- Larger area under the curve (I is proportional to kEV squared)
- Line tails off at new tube current/kEV max.
- Characteristic lines
What does ‘intensity’ refer to?
Number of x-ray photons in the primary beam per unity time
What does ‘beam quality’ refer to?
Penetrating power of the beam and is dependent on kV
What does ‘beam quantity’ refer to?
Number of photons in the x-ray beam. It is dependent on mA (tube current) and kV (potential difference across tube)
Which x-ray photon interaction is proportional to atomic number cubed (Z3)?
Photoelectric absorption
This makes it useful for imaging regions of similar atomic densities (low subject contrast), by highlighting the differences in regions by a factor of cubed.
Which photon interaction is inversely proportional to energy cubed (1/E3)?
Photoelectric absorption. I.e. increasing energy decreases the occurance of PEA by a factor of 3.
How does photoelectric absorption affect absorbed dose?
Ejection of an electron (ionisation) of atoms in the body lead to the release of small amount of characteristic radiation. Atoms in the body are small so the energy of these photons is low and are absorbed by the tissues.
