Quiz3 Mon. 9/30 Flashcards
Does the grid have anything to do with production of 2nd radiation
- no
* primary purpose to absorb (scatter)
Grid ratio / formula
- H/D
* hight of the grid strips to the distance in between
Grid frequency / high grid frequency=
- # of grid strips per inch
- higher frequency= fewer grid lines, absorb more scatter,
- but increase patient dose
Which would have better grid clean up if two grids have the same ratio but different frequency?
•the grid with the higher frequency
Grid cutoff
•primary beam / useful beam is blocked from reaching the image receptor can be partial or complete
What grid ratio gives patients highest dose
•16:1 the higher the grid ratio the more patient dose
Which grid requires the least amount centering
•parallel
What has more grid lines stationary grids or moving grids?
•stationary grids
Grid types
- parallel ||||| most forgiving, simple
- crosshatch # must be centered, better cleanup
- focused //|||\
Grid problems
- off level-grid or tube is not even/leveled
- off center-tube is not centered with grid (most often crosshatch)
- off focused-not using the proper SID
- upside down-
Air gap technique
- is equal to 8:1 grid
- I.R. Is 10-15 cm or 5 inch from patient
- requires increase SID to compensate for OID
- requires increase in mAs of 10% increasing patient dose
Affects of grid ratio Patient dose
- dose increases as ratio increases
* but as kVp increases dose decreases
Moving grids require how much more radiation to patient
- 15% more radiation
* however advantages far out way the disadvantages
Grid selection below 90 kVp and above 90 kVp
- below 90 kVp 8:1
- above 90 kVp higher ratio grid
- higher kVp produces more scatter requiring higher ratio grid
Grids improve
•image quality & contrast
