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Rad Grids
| Question | Answer |
|---|---|
| what would be the only advantage of a linear parallel grid over a linear focus grid? | place grid at any SID |
| what is the advantage of a focus grid over a linear grid | do not get grid cutoff, only in periphery |
| if you have a situation where you had no control over SID then what grid would you want to use? | parallel grid |
| what is defined by the loss of density due to absorption of the image forming beam by the lead strips | grid cutoff |
| 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 |
| what is grid focusing range or grid radius when we have a focus grid | * |
| whats the purpose of a potter bucky moving grid? what are the two motions it moves? | move out the grid line. oscillating and receptacle |
| does the grid start before or after exposure | before, and has to continue until after |
| 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 |
| 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 |
| what are the rules of thumb for using a grid | greater 60 Kvp and more than 10cm in pathology |
| whats the formula for grid ratio | h/D |
| what are some common grid ratio's we might use? | 5:1, 2:1, 6:1, High ratio 16:1, 10:1, 12:1 |
| what is defined when the number of lead strips per unit measure. how does that help determine the efficency of a grid? | grid frequency. * |
| if we were doing film screen technology what would be the most efficent grid you could buy | high ratio low freq |
| bucky factor | amount of exposure patient recieves with a grid vs. without a grid. |
| contrast improvement factor | looks at the contrast on image with a grid vs. a contrast on a image without a grid |
| what is the air-gap | * |
| whats an alternative when using film screen technology | backwards cassette |
| with electronic imaging, what causes the moire effect | thick lead lines |
| what is the type of radio-opaque material used for grids | lead |
| what are some types of radio lucicent material used for grid | carbon fiber, plastic, aluminum |
| what two factors determine grid efficency | grid ratio and frequency(amount of lead) |
| what is a disadvantage of using a grid | increase patient dose |
| what is the main purpose of a grid | clean up scatter |
| if we clean up scatter what happens to contrast | Increases |
| when we use a grid why do we have to increase technique. | because everything is being absorbed |
| what % of the useful density is from scatter on a chest? abdomen | 50, 90 |
| what is scatter | weaken photons from patient that change direction |
| what technical factor controls amount of scatter produce | kvp |
| what are some patient factors that control amount of scatter | pathology,type of tissue,thickness |
| if you use a grid that is more efficent would we clean up more or less scatter | more |
| what are two ways a manufacture can make a grid more efficent | high grid ratios(thiner interspace), low frequency (thicker lead lines) |
| so if you have less of an interspace and thick lead lines, very effiecent grid. do you have a lot of positioning latitude | no |
| if we clean up scatter properly what does that do to our image. how does it improve the image | better contrast, improved visibility detail |
| what is contrast | density difference, more black than white |
| 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 |
| which with electronic imaging system do the recomend today which better meets ALARA standards | kvp |
| where is the highest % of scatter produced | 180 degrees highest quanity , but 90 degrees gets the highest intesty |
| scatter is what % or what fraction of the xray photon | 1/1000 or .1% |
| which two tissues in your body make the most scatter | adipose, muscle(fluid filled) |
| do grids have anything to do with production of scatter | No, But they will reduce after it is produced. |
| 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 |
| what do we use for abd work | low kvp 70-80, so use intermediate speed grid(10:1, 12:1) |
| what grid ratio do we use on portable xrays | 8:1 |
| why is it better to do kvp than mas | less patient dose |
| 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) |
| 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 |
| of focus grid was upside down on chest xray where would you see the cutoff | severe peripheral, where both lung shadows should be |
| where would you see cutoff if you have a grid that was off center | more to one side than another |
| what is the purpose of using a focus grid vs. a parallel grid | to prevent periphreal cutoff, |
| what happens if we dont use right SID | periphreal |
| where would be the cutoff if the central ray is perpendicular to grid lines | image would be light* |
| 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 |
Created by:
johnsoni1986
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