cassette and IS
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| function of a cassette | portable light proof case for film to protect it from light
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| name the layered parts of a cassette | cassette thats radiolucent,IS, film,IS,cassette w/lead backing
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| what is the test for poor contact for film and IS | wire mesh test for fuzziness, space or poor contact
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| the IS provides added ________ to the image | added density if area of phosphers are blocked there will be a white spot on image
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| what are some types of holders | cardboard like envelope,conventional w/latches,double and single screens like sandwich,CVD cassettes
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| what are IS used for | to amplify incoming x-rays,forms 99% of latent image,reduces PT radiation
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| how does the IS absorb radiation | photoelectric light
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| what are the two types of luminescence | fluorescence-instantaneous and phosphorescence-delayed
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| what are some names for delayed phosphorescent emission | screen lagg or afterglow,,happens w/aging phosphers
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| what is the IS coated with | radiolucent plastic coating
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| what are the layers of an IS | base,relflective layer,phospher layer,protective layer
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| what is the base of the IS made of | polyester plastic 1mm thick has to be flexible,rigid,chemically inert,radiolucent
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| what is the reflective layer of the IS made of | magnesium oxide or titanium dioxide 25mi thick that reflects light back toward film,decreases PT radiation by adding more light to the image
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| what is the phosphor layer of the IS known as | the active layer,converts active photons to light photons
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| what makes up the protective layer of the IS | protective plastic appled to top of phospher to allow cleaning,prevent scratches and build-up of static electricity
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| what are two factors affecting IS speed | resolution controlled by crystal size and density,speed-more phosphors and higher kV more speed but less detail
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| what are the screen speeds labeled as and the formula | Releative SpeedRs1(mAs1)/Rs2=mAs2
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| why are rare earths the preferred phosphors | they have great absorption abilities,intensification factors and conversion of efficiency
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| two rare earths that offer increased speed and maintain resolution | lanthanum and gadolinium
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| qualities in choosing a phospher for IS | not to deteriate rapidly,not a lg amount of light per interaction,low enough atomic number,no afterglow and provide uniform quality
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| criteria for good recorded detail provided by IS | thin layer of crystals,too much will give off too much light
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| quantum mottle is most often seen in what kind of exam | fluoro,an increase in mAs will prevent it
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| some problems with cassettes are | droppping them causes bending and hinges and compression bands to loose contact w/film making images fuzzy
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| film speed is dependent on | the size of the crystals
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| fast film has more or less crystals | more or larger, makes it faster because they need less exposure to be ionized,but grainier images
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| if the film is too white,not enough density what is the most common fault | mAs or kV too low
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| what is the main function of screens | to reduce PT radiation
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| what are phosphors | they convert photon energy into light
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| what is the criteria for film speed and its down fall | thicker phosphor layer,higher absorption,but decreased resolution
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| the purpose or the back of the cassette being lined with lead is | to absorb secondary radiation so not to have back scatter get back to the film
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| what are artifacts | unwanted marks or images on a radiograph
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| felt padding is for | to ensure secure contact w/film
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| what are intensifying screens | thin sheets or layers of fluorescent that is housed in a cassette,x-ray energy is absorbed by material and converted to light
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| why are two IS seen more often than one | one is mostly seen in mamography for fine detail,two increase absorption and receptor sensitivity of image blurring
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| when is x-ray absorption most probable | when photon energy is just slightly higher than k-energy of absorbing material
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| lanthanum and gadolinium,rare earths, are most used for what reason | k-edge of these elements is in the x-ray beam spectrum whichh increase the chance of x-ray interaction and absorption
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| is speed and sensitivity constant for a an intensifying screen or is there a dependent variable | kV selected for specific exams changes speed and sensitivity
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| purpose of IS is to add ________ on film of x-ray exposure | blackening effect
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| early phosphors such as calcium tungstate emitted a _______ emitter | blue
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| lanthanide series are also called | rare earth elements
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| what are the atomic numbers for the rare earths | 57-71 and 39 has same properties
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| what is the function of the activator mixed with the phosphor layer and name | enhance light output in speed and wavelength Terbium and Europium w/Terbium are most used
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| does x-ray absorption increase or decrease with atomic number of the phosphor | increases
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| quantum mottle is due to | non even light emission from the IS,irregular spread of image points
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| Screen Speed is | amount of luminance for a given x-rayex. 200 screen needs half the exposure than a 100 screen
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| describe relationship of screen speed and light emission | direct relation-faster screen,more light emitted for same intensity of exposure
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| describe the relationship of screen speed and PT dose | inverse relation-as speed increases less radiation necessary and radiation decreases, slower screens need more radiation thus upping PT dose
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| screen speed and density have what type of relation | direct-as screen speed increases with the same exposure factors, density increases -as screen speed decreases density decreases
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| why are rare earths phosphors so much faster than calcium tungstate | increased absorption and conversion factors
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| poor screen contact can be caused by | warped,bent or broken cassette
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| why do some IR contain lead foil | to stop backscatter from fogging the film
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| does the IS need to be protected from light | no
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| poor screen contact could cause | blurred image
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| single IS raise PT dose but are used for | better recorded detail
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| a 200 speed screen with the same technical factors shows less or more density than a 50 screen | more density, more crystals to produce density
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| when comparing a 50 to 100 speed screen which one would require a greater exposure | 50 speed less dense crystal thickness to produce image
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| Principle action of the crystals in IS is to produce | x-rays into visible light
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| rare earths predominently give off what color emittance | blue and green
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| quantum mottle is mostly seen in high or low speed systems | high speed, irratic exposure
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| film speed can be increased by | thickness of phosphor layer and adding reflective backing to phosphor layer
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| resolution can be improved by | adding dye to slow speed or using slower speed screen
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| what is spectral matching | to obtain maximum efficiency from a film-screen IR light emitted by screens should correspond to maximum light sensittivity of the film
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| the amount of x-ray absorption by IS phosphor is dependent upon | photo electric effect
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| resolution is measured in | lines pairs per millimeter
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| what is conversion efficiency | ratio of the x-ray energy absorbed by a phosphor to the visible light energy emitted
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| the front of cassette must be covered by a light tight substance that is | homogeneous and radiolucent to keep one density through out
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| describe the affect of density because of thickness layer of phosphor | SMALLER crystal size, less dense layer will darken smaller area of a film-LARGER more density of crystals will darken or produce more larger area of darkness to film
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| poor contact between film and IS increases or decreases image density | decreases
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| when screen speed is increased should technique be increased or decreased to maintain density | decrease technique with higher more dense layers of phosphor IS
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| why are rare earths mixed with an activator like Terbium | they do not fluoresce well
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| describe the intensification facor of IS | increase kV more absorption of x-rays in screen, more intensification
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| calcium tungstate has a conversion efficiency of____% and rare earths are between ______% | 5% for calcium tungstate and 15-30% for rare earths
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