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Flashcards in Grids Deck (8)
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Why are grids used

When higher voltage used for thick tissues some x-rays undergo changes and emerge as scatter
Results in image blur

Used with areas >10cm


Describe grid construction (general)

Flat plate with lead strips separated by radiolucent material
Lead strips absorb scatter


Describe parallel grid construction

Vertical parallel strips
Edge of beam may also be absorbed along with scatter resulting in cut-off


Describe focussed grid construction

Strips angled to correspond with divergence of x-rays
Prevents cut-off


Describe pseudo-focussed grid construction

Vertical strips shorten towards edge
Reduced absorption and cut-off


Describe moving grid construction

Strips move slightly during exposure
Prevents parallel lines on final image
Req. connection between machine & grid (PBS)


Describe crossed grid construction

Strips running in both directions
Greater scatter absorption


How do grids affect exposure settings

Exposure time must be increased due to absorption by grid
mAs must be multiplied by grid factor to counteract potential under-exposure