Scatter Reduction Flashcards
what do scattered photons do to an image
they degrade the image
what two things does scatter reduce
scatter reduces both image contrast and image quality
what is compton scatter responsible for?
impaired tissue contrast and staff doses
what are the ways of reducing scatter?
collimation
patient compression
anti-scatter grid
air-gap technique
reduce kVp
what is a collimator
a collimator incorporates a series of blades usually made of lead which can shape the beam into rectangular or square fields, incorporates a light to outline the beam profile
what does patient compression improve in terms of the image obtained?
improves spatial resolution and tissue contrast
what are antiscatter grids made of and what is the arrangement?
anti-scatter grids are made of lead strips separated by either aluminum or carbon fibre interspaces
what % of scattered radiation do grids attenuate?
grids attenuate 80-90% of scattered radiation
how is the grid ratio defined?
grid ratio = h/D
h = height of lead strips
D = distance between lead strip
higher the grid ratio…
more effective at reducing scatter
what is the grid frequency?
the number of grid lines per cm
what can happen if there is poor positioning of the grid
there can be a loss of primary radiation due to poor geometrical positioning of the grid, known as grid cut-off
name instances where grids are not used
in pediatrics and when x-raying the extremities
what do grids do during exposure?
grids oscillate during exposure to blur out grid lines in the radiograph
do grids increase or decrease patient dose?
grids increase patient dose
