Control Of Scatter & Grid Flashcards
What is a beam restricting device?
Tools an RT can use to limit the amount of scatter radiation reaching the IR.
What is scatter?
X-ray photons that have changed direction after interacting with matter.
What are three factors that contribute to scatter?
Increased kVp
Increased X-ray field size
Increased pt thickness
Beam restricting devices reduce scatter by:
Decrease X-ray beam
Decrease amount of tissue irradiated
As scatter radiation increases, the radiograph loses contrast & appears:
Gray and dull due to fog.
Fog is:
Unintended optical density on a radiograph that reduces contrast because of light or chemical contamination.
Three effects of scatter:
Degrades visibility of detail or image detail
Degrades contrast resolution
Degrades spatial resolution
Spatial resolution is controlled by:
Focal spot size.
Contrast resolution is affected by:
Scatter radiation
Scatter can be controlled by:
Beam restricting devices, grids & collimation.
Collimation reduces _________ & improves _________.
Pt dose/contrast resolution
As X-ray energy increases (kVp) scatter (increases or decreases?)
increases
It is not possible to use low kVp on all of our exams because:
Fewer X-rays reach the IR at low kVp (Higher percentage of a low energy beam gets attenuated by the pt).
With larger pt’s, kVp must be ______ (high or low) to ensure adequate penetration.
high
With increased kVp comes increased _______ and decreased _______.
Scatter/contrast.
Because of reduction in patient dose, ____ kVp is preferred to ___ kVp.
High/low
As field size is increased, scatter radiation is _______.
Increased.
As we collimate, we reduce the amount of OD as well as the amount of X-rays reaching the IR, therefore we must ______ our technique.
increase.
Imaging thick parts of the body results in ___________ than when we X-ray thinner parts.
More scatter
Thicker body parts require (more or less) technique.
More
The angle of the scatter is greater in
the remnant beam.
A compression paddle can reduce the thickness of pt anatomy & bring the body closer to the IR, and therefore:
Improves spatial resolution.
Reasons to restrict the X-ray beam:
Only the part being examined should be exposed and large X-ray fields result in more scatter radiation.
Types of beam-restricting devices:
Aperture diaphragm
Cones
Cylinders
Collimators