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