Help
Options
Didn't know it?
click below
click below
Knew it?
click below
click below
Don't Know
Remaining cards (0)
Know
retry
shuffle
restart
0:00
Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.
Normal Size Small Size show me how
Normal Size Small Size show me how
Grids
Grids Review
| Question | Answer |
|---|---|
| what is the energy of the scattered xrays 1 meter from the pt. | .1% or 1/1000 of primary beam |
| what are the patient factors that affect scatter radiation | -tissue density -size of part -atomic # of tissue -atomic mass of tissue -beam restriction *barium causes more scatter |
| what percentage of scatter makes up the useful density on a chest xray | 50% |
| what percentage of scatter makes up the useful density on a abdomen xray | 90% |
| what happens if you have too much scatter | -fogs image -reduces contrast -reduces visibility of detail |
| what is the purpose of an xray grid | improves contrast by reducing the amount of scatter reaching the IR |
| where is the grid located | between the patient and the IR |
| when should we use a grid | -kVp higer than 60 -part thicker than 10-12 cm -pathology such as edema or ascites |
| how are grids constructed | alternating radio-opaque lead and radiolucent interspace(aluminum,carbon fiber,or plastic fiber) |
| what causes grid cutoff | loss of density due to absorbtion of unatenuated beam from pt |
| _________ grids cause grid cutoff on the periphery, but you can use any SID | parallel grid |
| __________ are the most commonly used grid. eliminates grid cutoff on periphery, but has limited SID(SID must be in focussing range to avoid cutoff) | focussed grids |
| cross type grid | can only be used in stationary bucky and provides no positioning lattitude |
| grid ratio | -determines grid efficiency along with amont lead in grid -R=H/D (H=heigt of strips, D=interspace distance) -ratio range=2:1-16:1 |
| grid frequency | -number of grid lines per unit of measurement -60-196 per inch or 152-498 per cm -80-103 lines/in or 203-261 lines/cm is common |
| what kind of grids are used for mobile imaging | -stationary -clip on -grid cassettes |
| potter bucky diaphragm | -grid is held inside bucky -recipricating or oscilating -motion statrts before exposure and ends after and is used to blur out grid lines |
| bucky factor | -measures grid quality by analyzing pt dose with a grid vs. dose w/o a grid -exit radiation vs radiation that actually forms image |
| when using a grid what must we do | increase mAs or kVp |
| using a grid does what to our gray scale | shortens it |
| contrast improvement ability | -measures grid quality by analyzing contrast with a grid vs. contrast w/o a grid -increased contrast improvement ability=increased contrast |
| what are the types of grid positioning errors | -upside down -off level -off center -off focus |
| causes severe peripheral cut-off and is the least common of grid errors | upside down grid |
| an angled grid or tube, causes cut-off over entire image due to oblique nature, CR cuts across or perpendicular to grid lines and is the most common of all grid errors | off level grid |
| causes cut-off of entire image with more on one side | off center(lateral decentering)grid |
| causes cut-off on periphery of image | off focus grid |
| stroboscopic effect | -in moving grids -motion of the grid is frozen -when using exposure time shorter than grid movement -reciprocating mechanism may be broken |
| what are some alternate methods of reducing scatter | -in film screen, you can use a backwards cassette -air gap technique |
| what is the rule for distance when using the air gap tecnique | for every inch of OID you must increase SID by a foot |
| focusing distance | specific range of SID's that can be used for focused grids |
Created by:
bigad1982
Popular Radiology sets