how is scatter produced?
xray photons interact w atoms in tissues and that causes them to change direction therefore creating scatter
why do we want the least amt of scatter to interact w the IR
becauyse it reduces image contrast
what helps to reduce scatter reaching the IR
collimation and grids
what does it mean for grid ratio and scatter if you have a smaller light field
gr- increase
s- decreased
how does having a taller grid affect grid ratio, scatter, and mAs
gr- increases
s- decreases
mAs- increases
gives us better image quality even tho theres a higher dose
what is the convergence line
where the lead strips would all meet if they were to extend to 100 or 180 cm. they are angled and will all join together as the beam would
what is the purpose of the grid ratio chart
it determines mAs
what type of grids are in the buckys? why?
moving grids, they move to blur the lead strip lines
what are the 2 types of moving grids
reciprocating- moves back and forth 2cm during expo
oscillating- moves in circular motion
what does the wine glass image indicate on a grid
indicates the tube side of grid
what info will be seen on all grids
grid ratio, focal distance, and lines/cm
what grid is used outside the bucky
stationary
what are stationary grids
used in moblie, may produce grid lines on image bc it doesnt move.
has thin strips
built in function called suppression which is a software on computer that removes grid lines from image
what does the centre line on a stationary grid mean
the direction of lead strips and where the middle is
what are the 3 lead strip positions? which do we commonly use?
linear parallel
linear focused - we use
criss-cross - mammography
explain what parallel grids are
lead strip does stright up and down.
often gets grid cut off at the edges and the edges will be brighter
when is grid cut off most noticeable w parallel grids
w short SID
explain what a cross grid is
strips are both vertical and horizontal bc they use two grids superimposed.
rarely used bc central ray and tube must be exact and not angled or else grid cut off
which grid strip position is best for scatter clean up
cross grid
explain what focus grids are
strips are focused to a point, if they were to be extended they would all meet at a point (100-180 cm) aka convergence line.
central ray must be centred to grid
why are the strips slightly angled on a focused grid
to match the beam as it leaves the tube
what are virtual grids
built into the software of a computer to improve image contrast after image has been taken.
used in mobile
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M1 L18
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M1 L2 basic elements6
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M1 L334
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cathode36
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anode30
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line focus principle M1L623
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anode heel effect M1L714
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tube preservation21
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M2 L1 scatter19
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M2 L2 collimator31
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M2 L3 intro to grids26
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M2L4 grid formulas14
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M2 L523
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M2 L6 grid errors14
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M3 L1 & 231
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M3 L3 & 416
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M3 L520
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M4 L1 & 230
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M4 L315
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M4L4 & questions from review15
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M5 L1, 2, & 329
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M5 L423
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M5 L5-732
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M6 L1-338
