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18 Cards in this Set
- Front
- Back
- 3rd side (hint)
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What is the major purpose of intensifying screens?
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To reduce patient dose by increasing efficiency of producing image and decreasing exposure level and time
(also increases tube life) |
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Most of the image is produced by visible light when using intensifying screen; true or false
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True, the x rays cause the phosphor crystals in the screen to glow that actually form the latent image
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Does use of an intensifying screen cause better recorded detail?
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No, the light spreads causes some blurriness
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What are the 4 parts of an intensifying screen?
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Base
Reflective layer Phosphor layer Protective coating Which is the active layer? |
The phosphor layer gives off light when stimulated by x-ray photons
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A good phosphor will have good ______________ , which is instant light reaction to x-rays but not ___________, which causes screen lag
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A good phosphor will have good Fluorescence, which is instant light reaction to x-rays but not Phosphorescence, which causes screen lag
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What is spectral emission of phosphors? and why is it important?
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Wavelength of light that is emitted by the screen. it must match the sensitivity of the film
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What is the only advantage of using rare earth phosphors over the older type?
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The conversion efficiency (ability to covert x-rays to light) These are at least twice as fast as older ones
5% compared to 15% efficiency get good resolution without over exposing patient. |
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What is one problem with using rare earth phosphor screen?
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Possibility of having "quantum mottle", which is radiographic noise because of using lower mAs
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What is the purpose of the reflective layer?
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Reflected light back to the film.
Is this used in rare earth screens? |
No, because of the greater efficiency of rare earth phosphors these are not needed
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Where is the base in relation to the film and what is it for?
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furthest away from the film and is a support for the phosphors, has to be chemically inert, radiolucent and flexible
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As crystal size goes up what goes up and what goes down?
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Speed goes up but recorded detail goes down....so resolution is inversely proportional to crystal size
What is the definition of resolution? |
The ability of a system to record an image
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How is resolution detail measured?
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In line pairs per millimeter, expressed as lp/mm
What is the best we can see with the naked eye? give the 3 levels of screen speeds and the resolution they are capable of: high speed, par and detail? |
naked eye: 10-20 lp/mm
detail: 15 lp/mm par: 10 lp/mm high speed 7 lp/mm |
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What is intensification factor and how is it arrived at?
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It is a ratio of a screen without a screen divided by one with a screen
film/screens are described as having a relative speed: Fine detail 20-80 RS Par speed 100 RS High speed 200 -1200 RS |
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What is the k-shell absorption edge of rare earth phosphor crystals and what is the advantage over older calcium tungstate crystals?
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the k-shell binding energy of the rare earths is lower than tungsten and can absorb 5 times more x-rays resulting in a dramatic increase in light production
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Because rare earths are more efficient screens than calcium tungstate and the crystal layer can be thinner what is the big advantage in using them?
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can reduce pt dose and get better recorded detail than having a thicker phosphor layer
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What is photoelectric absorption or interaction?
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When an x-ray photons match the k-shell electrons of phosphor
(tungsten atom has at #74, rare earths range 57-71) binding energy of W is 70 keV, rare earths are actually lower EXCEPT at k-shell binding energy which is why they are so good, they match causing an interaction which is the k-shell edge, giving better light production all in the 35-70kev range which is 40-75 kVp range |
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True or False
The back of the cassette is lined with lead to absorb with backscatter |
True, it is a very thin foil layer, which means you can actually use the cassette backwards but you would see artifacts
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Phosphors can be activated by what?
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Heat
Light Radiation |
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