Beam parameters, filtration, xray interactions Flashcards
What imapct does modifying tube current have on the energy spectrum?
Impacts the amplitude
Impact of modifying tube voltage on energy spectrum.
Impacts amplitude and position
Impact of modifying filtration on energy spectrum
impacts amplitude and shows most impact on lower energies.
Impact of modifying target material on energy spectrum
Amplitude and position of line (characteristic peak)
Impact of modifying voltage waveform on energy spectrum
Amplitude and shows most impact for higher energies.
Why is modifying the beam important?
It ensures that the overall patient dose is reduced and also overall dose for the other radiographers is also reduced.
What parameters increase x-ray quantity?
increasing mAs, kVp
What parameters decrease x-ray quantity?
increasing distance and filtration
How is x-ray quality defined?
As the penetrability of the beam.
How is x-ray quality measured?
HVL
What is half value layer?
the thickness of a material at which the intensity of radiation is reduced by a half.
How is the half value layer increased?
increasing kilovolt peak (kVp) = increasing quality of beam = increasing HVL
What is filtration?
The process of filtration is to remove low energy x-rays (by absorbing them) so the consequent beam is of high energy.
What one factor increases both quality AND quantity of a beam and how?
Tube voltage.
By changing the tube voltage, the potential difference between the anode and cathode is modified. As the electrons are accelerated, more x-rays reach the detector (increasing quantity) as well as there is an increase in overall beam energy (quality).
State the inverse square law
Intensity = 1/ distance^2
What are the 3 things that can happen when x-ray beams come into contact with a material?
They can be either absorbed, scattered or transversed w/o any interaction.
What does attentuation mean?
Attenuation refers to the x-rays that are absorbed and scattered.
Define mono and poly energetic energies.
Mono - a type of energy which which is fixed and does not change with attenuation at any depth. A hVL can be calculated for this type of energy.
Poly - Consist of both low and high energies. Low energy rays are absorbed faster and the high energy xrays are more penetrating. The hvl for this also keeps chagnging.
These are the beams we see in real life.
Why is filtration important?
- As lower energies are absorbed, the overall beam energy increases.
- The absorption of lower energy x-rays that dont add to the image, ensures that they are not absorbed by tissues (thus adding to patient dose).
What are the 2 types of filtration?
Inherent and added filtration
What is inherent filtration? What material does it use and at what thickness?
includes the windows of x-ray tubes and other enclosures of the tube itself.
The filter used is 0.5 mm of aluminium.
What is added filtration? What material does it use and at what thickness?
includes a thin layer of Al between the x-ray tube and the beam collimator.
The filter uses I mm of Al to filter the collimator.
Why is Al a good choice of filter?
- removes x-rays beams w/o decreasing beam intensity
- Lightweight and sturdy
- inexpensive
An alternative to Al for filter material?
copper
What is a compensating filter? Give an example.
it is a filter used when producing an image with non-uniform intensity (with varying thickness and tissue composition).
For e.g. a block filter is used when takingan x-ray of the foot (which is non-uniform).
