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43 Cards in this Set

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Film-screen combo summary

* faster-speed system
*higher contrast (blk/wht)
*narrow latitude
*less recorded detail
*increased density
speed controlled by...

contrast controlled by...
A. screen
B. film
Film-screen combo summary

* slower-speed system
*lower contrast (gray-scale)
*wider latitude
*greater recorded detail
*decreased density
Film-screen combo summary

* single emulsion films
*one intensifying screen
*slower
*lower contrast (grays)
*wider latitude
*better recorded detail
*decreased density
Film-screen combo summary

* double emulsion film
*2 intensifying screens
*faster
*higher contrast (blk/wht)
*narrower latitude
*pooper recorded detail
Identified by relative speed #'s - 100sp is base
*based on IF
exp w/o screens
IF = ---------------
exp w/ screens
thicker phosphor layer means
*increased screen speed
*decreased recorded detail
*decrease patient dose
lrg phosphor crystal sz means
*increased screen speed
*decreased recorded detail
*decreased patient dose
reflectv layer
*increased screen speed
*decreased recorded detail
*decreased patient dose
absorbing layer
*decreased screen speed
*increased recorded detail
*increased patient dose
dye in phosphor layer means..
*decreased screen speed
*increased recorded detail
*increased patient dose
200 screen sp system is twice as fast, so...
1/2 the mAs is required to produce same density
slower systems used for...

faster systems used for...
A. extremity radiography

B. spine, abd, trauma, peds
Spectral Matching
*wavelength of light emitted by screens must match w/ wavelengths to which film is most sensitive
film-screen contact
*must be perfect
*poor contact = loss of recorded detail
Film-screen contact tested by...
radiographing a wire/mesh screen
What are grids used for?
* to reduce the amt of scatter radiation reaching the film
Scatter travels in divergent paths and is...
* more likely absorbed in the grid
Grid Construction

lead strips separated by...
* aluminum interspacers

(increase technique)
Grid Ratio is
height of the lead strips divided by the distance between the lead strips
H/D
Ratios range frm 4:1 to 16:1
no grid - x1
4:1 - x2
6:1 - x3
8:1 - x4
12:1 - x5
16:1 - x6
Grid Frequency is...
* Number of lead strips per inch (centimeter)
what do grids do?
* reduce the amt of scatter reaching film
scatter travels...

image producing rays...
A. in divergent paths

B. perpindicular path
scatter is...
likely absorbed in the grid
grids are used when...
* parts are more than 10 cm thick
grid construction

lead strips separated by...
* aluminum interspaces
grid ratio
* height of the lead strips divided by the distance between the lead strips
H/D
grid frequency
* number of strips per inch

* as grid frequency increases, lead strip thickness decreases and becomes less visible
grid frequency ranges frm???
* 60 to 150 lines per inch
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
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
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
grid characteristics

contrast improvement factor??
* measure of a grids ability to increase contrast

* expressed as ratio of contrast w/ grid to w/o grid
grid selectivity
* 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
grid conversion factor (known as bucky factor)
* 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
grid motion

stationary grids
* do not mv during exposure
* grid lines may be seen
grid motion

moving grids
* mv back and forth during exposure
* eliminate visibility of grid lines
grid characteristics

contrast improvement factor??
* measure of a grids ability to increase contrast

* expressed as ratio of contrast w/ grid to w/o grid
grid selectivity
* 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
grid conversion factor (known as bucky factor)
* 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
grid motion

stationary grids
* do not mv during exposure
* grid lines may be seen
grid motion

moving grids
* mv back and forth during exposure
* eliminate visibility of grid lines