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Flashcards in Grids Deck (8)
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1

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

2

Describe grid construction (general)

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

3

Describe parallel grid construction

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

4

Describe focussed grid construction

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

5

Describe pseudo-focussed grid construction

Vertical strips shorten towards edge
Reduced absorption and cut-off

6

Describe moving grid construction

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

7

Describe crossed grid construction

Strips running in both directions
Greater scatter absorption

8

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