Rad Grids
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| what would be the only advantage of a linear parallel grid over a linear focus grid? | place grid at any SID
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| what is the advantage of a focus grid over a linear grid | do not get grid cutoff, only in periphery
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| if you have a situation where you had no control over SID then what grid would you want to use? | parallel grid
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| what is defined by the loss of density due to absorption of the image forming beam by the lead strips | grid cutoff
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| if you have two grids, either linear focus or linear non focused perpedicular to each other would be ....? is there any positioning latitude then? | Crossed Grid. No
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| what is grid focusing range or grid radius when we have a focus grid | *
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| whats the purpose of a potter bucky moving grid? what are the two motions it moves? | move out the grid line. oscillating and receptacle
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| does the grid start before or after exposure | before, and has to continue until after
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| what is the definition of grid ratio | the height of the grid divided by the interspace width. grid ratio= h/D h(height of grid) D(Interspace material) it can be aluminum(Best), plastic or carbon fiber
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| if we have a higher ratio grid which we would use anytime when thier is more scatter produced, what would happen to interspace? would the grid be more or less efficent? | get smaller. More
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| what are the rules of thumb for using a grid | greater 60 Kvp and more than 10cm in pathology
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| whats the formula for grid ratio | h/D
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| what are some common grid ratio's we might use? | 5:1, 2:1, 6:1, High ratio 16:1, 10:1, 12:1
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| what is defined when the number of lead strips per unit measure. how does that help determine the efficency of a grid? | grid frequency. *
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| if we were doing film screen technology what would be the most efficent grid you could buy | high ratio low freq
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| bucky factor | amount of exposure patient recieves with a grid vs. without a grid.
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| contrast improvement factor | looks at the contrast on image with a grid vs. a contrast on a image without a grid
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| what is the air-gap | *
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| whats an alternative when using film screen technology | backwards cassette
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| with electronic imaging, what causes the moire effect | thick lead lines
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| what is the type of radio-opaque material used for grids | lead
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| what are some types of radio lucicent material used for grid | carbon fiber, plastic, aluminum
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| what two factors determine grid efficency | grid ratio and frequency(amount of lead)
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| what is a disadvantage of using a grid | increase patient dose
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| what is the main purpose of a grid | clean up scatter
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| if we clean up scatter what happens to contrast | Increases
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| when we use a grid why do we have to increase technique. | because everything is being absorbed
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| what % of the useful density is from scatter on a chest? abdomen | 50, 90
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| what is scatter | weaken photons from patient that change direction
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| what technical factor controls amount of scatter produce | kvp
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| what are some patient factors that control amount of scatter | pathology,type of tissue,thickness
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| if you use a grid that is more efficent would we clean up more or less scatter | more
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| what are two ways a manufacture can make a grid more efficent | high grid ratios(thiner interspace), low frequency (thicker lead lines)
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| so if you have less of an interspace and thick lead lines, very effiecent grid. do you have a lot of positioning latitude | no
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| if we clean up scatter properly what does that do to our image. how does it improve the image | better contrast, improved visibility detail
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| what is contrast | density difference, more black than white
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| if we increase the ratio of the grid to make it more efficent, what do we have to do to our techniques to compenstate for the loss of density | increase technique(mAs, Kvp), patient does increase
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| which with electronic imaging system do the recomend today which better meets ALARA standards | kvp
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| where is the highest % of scatter produced | 180 degrees highest quanity , but 90 degrees gets the highest intesty
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| scatter is what % or what fraction of the xray photon | 1/1000 or .1%
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| which two tissues in your body make the most scatter | adipose, muscle(fluid filled)
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| do grids have anything to do with production of scatter | No, But they will reduce after it is produced.
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| if we are doing a chest at the chest board what kvp do we use. if we have high kvp would we have more or less scatter produced, then would we want to use a what type of ratio grid | 117 high. thicker than 10 cm, so use grid. more, higher
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| what do we use for abd work | low kvp 70-80, so use intermediate speed grid(10:1, 12:1)
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| what grid ratio do we use on portable xrays | 8:1
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| why is it better to do kvp than mas | less patient dose
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| for mAs ratio 5:1, 6:1, 8:1, 12:1, 15:1 what do you multiply by (for non grid to grid) | 5:1(2), 6:1(3), 8:1(4), 12:1(5), 15:1(6)
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| what is the definition of grid cutoff | loss of density due to bad angle that causes image forming rays to be absorb by lead strips
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| of focus grid was upside down on chest xray where would you see the cutoff | severe peripheral, where both lung shadows should be
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| where would you see cutoff if you have a grid that was off center | more to one side than another
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| what is the purpose of using a focus grid vs. a parallel grid | to prevent periphreal cutoff,
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| what happens if we dont use right SID | periphreal
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| where would be the cutoff if the central ray is perpendicular to grid lines | image would be light*
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| if we use a grid and dont change technique whats going to happen to density | go down, so increase kvp or mas to maintain it, and the contrast improves
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