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43 Cards in this Set
- Front
- Back
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Film-screen combo summary
* faster-speed system |
*higher contrast (blk/wht)
*narrow latitude *less recorded detail *increased density |
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speed controlled by...
contrast controlled by... |
A. screen
B. film |
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Film-screen combo summary
* slower-speed system |
*lower contrast (gray-scale)
*wider latitude *greater recorded detail *decreased density |
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Film-screen combo summary
* single emulsion films |
*one intensifying screen
*slower *lower contrast (grays) *wider latitude *better recorded detail *decreased density |
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Film-screen combo summary
* double emulsion film |
*2 intensifying screens
*faster *higher contrast (blk/wht) *narrower latitude *pooper recorded detail |
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Identified by relative speed #'s - 100sp is base
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*based on IF
exp w/o screens IF = --------------- exp w/ screens |
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thicker phosphor layer means
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*increased screen speed
*decreased recorded detail *decrease patient dose |
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lrg phosphor crystal sz means
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*increased screen speed
*decreased recorded detail *decreased patient dose |
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reflectv layer
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*increased screen speed
*decreased recorded detail *decreased patient dose |
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absorbing layer
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*decreased screen speed
*increased recorded detail *increased patient dose |
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dye in phosphor layer means..
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*decreased screen speed
*increased recorded detail *increased patient dose |
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200 screen sp system is twice as fast, so...
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1/2 the mAs is required to produce same density
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slower systems used for...
faster systems used for... |
A. extremity radiography
B. spine, abd, trauma, peds |
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Spectral Matching
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*wavelength of light emitted by screens must match w/ wavelengths to which film is most sensitive
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film-screen contact
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*must be perfect
*poor contact = loss of recorded detail |
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Film-screen contact tested by...
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radiographing a wire/mesh screen
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What are grids used for?
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* to reduce the amt of scatter radiation reaching the film
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Scatter travels in divergent paths and is...
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* more likely absorbed in the grid
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Grid Construction
lead strips separated by... |
* aluminum interspacers
(increase technique) |
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Grid Ratio is
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height of the lead strips divided by the distance between the lead strips
H/D |
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Ratios range frm 4:1 to 16:1
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no grid - x1
4:1 - x2 6:1 - x3 8:1 - x4 12:1 - x5 16:1 - x6 |
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Grid Frequency is...
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* Number of lead strips per inch (centimeter)
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what do grids do?
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* reduce the amt of scatter reaching film
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scatter travels...
image producing rays... |
A. in divergent paths
B. perpindicular path |
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scatter is...
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likely absorbed in the grid
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grids are used when...
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* parts are more than 10 cm thick
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grid construction
lead strips separated by... |
* aluminum interspaces
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grid ratio
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* height of the lead strips divided by the distance between the lead strips
H/D |
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grid frequency
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* number of strips per inch
* as grid frequency increases, lead strip thickness decreases and becomes less visible |
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grid frequency ranges frm???
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* 60 to 150 lines per inch
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grid types
* linear grids |
* lead strips are parallel
* tube may be angled along the length of the grid w/o cutoff * grid cutoff-decreased density along the periphery of the image caused by absorption of image-forming rays * used w/ lrg sid or sm field |
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grid types
* focused grids |
* lead strips are angled to coincide w/ divergence of xray beam
* used specific ranges of SID * grid radius: distance at which focused grid may be used * focal range is wide for low-ratio grids * focal range is narrow for high-ratio grids * focal range is stated on the front of the grid |
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grid types
* crossed grids |
* also known as crosshatch
* consist of 2 linear grids placed perpindicular to each other * superior clean-up * no angulation of xray beam * requires perfect positioning & centering * primary use is biplane cerebral angiography |
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grid characteristics
contrast improvement factor?? |
* measure of a grids ability to increase contrast
* expressed as ratio of contrast w/ grid to w/o grid |
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grid selectivity
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* espressed as ratio of primary rad transmitted thru grid to 2nd rad transmitted thru the grid
* higher grid frequency & grid ratio, the more selectv it will be * high selectv, high efficiency of scatter cleanup |
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grid conversion factor (known as bucky factor)
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* amt of increased tech to compensate for absorption of scatter and image forming ray
* used to indicate increase in mAs when converting frm grid to nongrid * grid conversion factors increase w/ higher kVp due to increased Comptons |
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grid motion
stationary grids |
* do not mv during exposure
* grid lines may be seen |
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grid motion
moving grids |
* mv back and forth during exposure
* eliminate visibility of grid lines |
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grid characteristics
contrast improvement factor?? |
* measure of a grids ability to increase contrast
* expressed as ratio of contrast w/ grid to w/o grid |
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grid selectivity
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* espressed as ratio of primary rad transmitted thru grid to 2nd rad transmitted thru the grid
* higher grid frequency & grid ratio, the more selectv it will be * high selectv, high efficiency of scatter cleanup |
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grid conversion factor (known as bucky factor)
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* amt of increased tech to compensate for absorption of scatter and image forming ray
* used to indicate increase in mAs when converting frm grid to nongrid * grid conversion factors increase w/ higher kVp due to increased Comptons |
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grid motion
stationary grids |
* do not mv during exposure
* grid lines may be seen |
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grid motion
moving grids |
* mv back and forth during exposure
* eliminate visibility of grid lines |
