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Screens
Screen review
Question | Answer |
---|---|
what is the purpose of intensifying screens | converts small quantity of xrays to larger quantity of light photons |
what are the advantages of intensifying screens | -less pt dose -less wear and tear on the euipment |
what is the disadvantage of intensifying screens | low spatial resolution |
how are screens constructed | -base layer -reflective layer -phosphor/active layer -protectcive coat |
functions to provide mechanical support for phosphor | base layer |
-redirects isotropically emitted light to film -uses 2x light, so it decreases pt dose, but loses spatial resoltin -detail screens use yellowish/brown light absorbing dye to absorb spread of long wavelength light which improves spatial resolution | reflective layer |
isotropic propagation | light emitted in all directions |
converts xrays to light/intensification | phosphor or active layer |
what color light would calcium tungstate phosphor give off | blue |
what color light would a pure rare earth phosphor give off | green |
when rare earth phosphors are combined with additional elements what color do they give off | blue violet |
what are the three rare earth phosphors | -gadolinium -lanthanum -yitrium |
between rare earth phosphors and calcium tungstate which has a higer DQE and conversion efficiency | rare earth |
as screen speed increases, does it give off more or less light | more |
what is the advantage of a fast speed screen | less dose |
what is the disadvantage of a fast speed screen | less spatial resolution |
what size crysatls give more speed | large |
do you have more speed with thick or thin emulsion | thick |
do you have more speed with or without a reflective layer | with |
what does excessive heat do to the speed of your screen | slows it down |
what is the test for resolution | line pair test(line pair bar phantom) |
what is spectral matching | matching the color light given off by the screen to film that is sensitive to that color |
clumping of phosphor causes what | screen structure mottle |
clumping of crystal in film causes what | film graininess |
low mas will cause what | quantum mottle |
what can cause poor film-screen contact | -worn felt -broken hinges or latches -foreign matter -warped cassettes -bent frame -trapped air(transitory-comes and goes) |
what does poor film-screen contact look like on a film | blurry spot |
what is the test used to detect poor film-screen contact | wire mesh test |
fluorescence | emits light only while stimulated |
phosphorescence | emits light for short period after stimulation has ended |
photostimuable | gives of luminescence twice |
spatial resolution/resolving power | ability to image an object faithfuly |
speed/sensitivity/coversion efficiency | how fast a minimal exposure is converted to light |
high DQE allows us to do what | lower our mas |
what will happen if you use a high speed screen with a technique for a slow speed screen | you will over expose the film(therefore you would underexpose film if you used a low speed screen with a high speed technique) |
if you only cared about pt dose what film/screen combo would you use | fast/fast |
if you only cared about image quality or resolution what film/screen combo would you use | slow/slow |
if you wanted a good balance between dose and resolution what are your film/screen options | -fast/slow -medium/medium |
what is the main purpose of a film cassette | -light tight -good film/screen contact |
what is the purpose fo the protective coat | -protects from abrasions,stains,and scratches(white line artifact) -provides cleaning surface |
how is tube side of cassette constructed | -radioluscent -carbon fiber or bakelit |
how is backside of cassette constructed | -radiopaque -w/ lead foil to prevent backscatter |
what is the primary difference between the imaging plate cassette and film cassette | blocker |
what is spatial resolution in film screens dependant upon | -phosphor crystal size -phosphor layer thickness -phosphor concentration -type of phosphor -reflective layer -yellow light absorbing dye |
what is the modular transfer function to measure resolution | measures information lost between subject an IR caused by light diffusion |
what is the line spread function to measure resolution | microdesitometer to measure the film screen combos ablility to accurately measure boundries of images |
what is intensification factor | exposure with a screen vs. exposure w/o a screen |