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RADT 412
Exposure- unit 2
| Question | Answer |
|---|---|
| the layers of an intensifying screen in order are: | base, white reflecting surface, active layer, and protective coating |
| a material that gives off light when struck by x-ray photons is called: | phosphor |
| in places where a large amount of radiation got thru the patient's body, the intensifying screen would give off _____ of light, and this area on the radiograph would be developed as _____ | large amount, black |
| which are the 2 main parts of an intensifying screen? base and emulsion, base and active layer, emulsion and active layer, or active and protective layer | base and active layer |
| delayed light emission of an intensifying screen after the xray photons have been turned off is called | phosphorescence |
| which one of these is the phenomenon that causes a loss of recorded detail with intensifying screens? afterglow, light diffusion, phosphorescence, or fluorescence | light diffusion |
| fast screens emit _____ light than slow screens | more |
| changing from a slower screen to a faster screen will have what effect on the patient's radiation dose | it will decrease dose |
| the part of the active layer of an intensifying screen that produces light is the: | phosphor |
| an area of poor screen contact occurs: | when there is an increased distance between the screen and film inside the cassette |
| changing from a slower screen to a faster screen will have what effect on density | it will increase it |
| a relative speed value of 100 corresponds to a: | medium speed screen |
| the ability of a material to give off light when struck by xrays is called: | fluorescence |
| increasing the speed of an intensifying screen also increases | light diffusion |
| a test for poor screen contact is performed with which one of these devices | a wire mesh |
| changing from a slower screen to a faster screen will have what effect on recorded detail | it will decrease it |
| which one of these systems would require the highest mAs to produce the image? direct exposure, calcium tungstate screen system, computed radiography, or rare earth screen system | direct exposure |
| the color of light given off by a rare earth intensifying screen is: | yellow green |
| which one of these systems is usually better for producing a low radiation dose to the patient? calcium tungstate, rare earth, or direct exposure | rare earth |
| the type of film used with an intensifying screen and the safelight used must be matched with the type of screen | fluorescence |
| the brightness of a computed radiography image is similar to the film/ screen system quality of: | density |
| the 2 different intensifying screen systems in use today are: | rare earth and calcium tungstate |
| conversion efficiency is the ability to convert: | xray energy to light energy |
| direct exposure systems produce good recorded detail because: | no light is used to record the image |
| the recorded detail of a computed radiography system is determined by: | the number of pixels used in the matrix |
| list 7 factors that affect recorded detail | SID, OID, focal spot, screen speed, film speed, film/ screen contact, and motion |
| which one of these help the film travel from one processing section to the next? turnarounds, crossovers, guide shoes, or entrance rollers | crossovers |
| the layer of film that touches the protective coating of the intensifying screen in a closed cassette is the: | supercoating |
| one type of film used to record an image from a computer screen is: | laser film |
| the device used to test the resolution of a film/ screen imaging system is a: | resolution grid |
| if the OID is decreased, unsharpness ____ and recorded detail ____ | decreases, increases |
| what is the amount of unsharpness if the focal spot size is a .6, the OID is 7 inches, and the SID is 40 inches: | .13 |
| what new mAs should be used when changing from a 100-speed screen to a 400-speed screen if 5 mAs was used originally | 1.25 |
| film emulsion is composed of | silver bromide and gelatin |
| if the SID is increased, unsharpness ____, and recorded detail _____ | decreases, increases |
| which one of these chemicals is the hardener used in the developer? sodium sulfite, glutaraldehyde, potassium bromide, or hydroquinone | glutaraldehyde |
| which one of these processor sections clears the film of unexposed and undeveloped silver bromide? wash, dryer, developer, fixer | fixer |
| if the focal spot is decreased, unsharpness ____ and recorded detail ____ | decreases, increases |
| which one of these intensifying screen systems gives off a yellow-green light? rare earth or calcium tungstate | rare earth |
| poor screen contact is tested with a: | wire mesh |
| which one of these agents stops developer action? hardener restrainer, activator, preservative | activator |
| which one of these agents reduces the exposed silver bromide crystals to metallic silver? fixing, developing, hardener, preservative | developing |
| if the intensifying screen speed is increased, unsharpness ____ and recorded detail ____ | increases, decreases |
| which chemical is responsible for producing the fray tones of the image? acetic acid, hydroquinone, phenidone, or sodium sulfate | phenidone |
| which one of these has the least effect on recorded detail? SID, OID, screed speed, or film speed | film speed |
| where is base-plus-fog measured | on any blank area of the film |
| the ability of an imaging system to record 2 adjacent structures as separate structures is: | resolution |
| if magnification increases: | recorded detail decreases |
| the blue tint of the film base stops how much light from getting through it | 15% |
| which is the correct order for film travel through the processor | developer, fixer, wash, dryer |
| the latent image is on the film | after exposure and before development |
| a developer temp that is too high may: | increase density |
| light diffusion | reduces recorded detail, caused by the space between the phosphor and film |
| which one of these intensifying screen speeds would produce the best recorded detail? 100 speed, 200 speed, 300 speed, or 400 speed | 100 speed |
| which one of these sysetems has the best conversation efficiency? direct exposure, calcium tungstate, rare earth, computed radiography | rare earth |
| calculate the amount of unsharpness with these conditions: 20 mAs, 70 kV, 1.5 mm focal spot, 2.5mm A1 filtration, 94 degree developer temp, 2 inch OID, 72 inch SID | .04 |
| calculate the new mAs to be used when changing from a 200 speed screen to a 600 speed screen when the origional exposure factors were: 500 mA, .05 sec, 80 kV, 12:1 grid | 8.5 |
| which term is the same as density in a computed radiography system? brightness, gray scale, resolution, or matrix | brightness |
| a quality system for an automatic processor measures: | speed, contrast, and base-plus-fog |
| which gets replinished in an auntomatic processor? wash, developer, and fixer dryer, developer, and fixer fixer and developer developer and wash | fixer and developer |
| what controls the film feeding rate and the replenishment rate? | the enterance rollers |
| base | has a white reflective surface, made out of cardboard or plastic, needs to be flexible, rugged, moisture resistance, and chemically inert |
| conversion efficiency | the number of light photons produced by one x-ray photon |
| luminescence | ability of a material to emit light |
| fluorescence | ability of a material to give off light when struck by xrays |
| intensifying screens | increase efficiency of xray absorption and decrease the dose of the patient |
| orthochromatic | film used with green light emitting rare earth intensifying screens |
| panchromatic | film used with calcium tungstate and other blue light emitting screens |
| protective coat | thin plastic layer about 25 micrometers thick that protects the phosphor layer from abrasion |
| phosphorescence | continued light emission after xrays have been turned off |
| quantum mottle | random speckled appearance of an image |
| rare earth screens | elements from the rare earth section of the periodic table, intensifying screens include gadolinium, lanthanum, and yttrium, 15-20% efficient in converting xray energy into light as compared to the calcium tungstate |
| phosphor | gives off light when struck by xray photons |
| what makes a screen faster? | add more phosphor layers and increase phosphor crystal size |
| there is an inverse between screen speed and what? | recorded detail |
| what is one of the rare earth elements used for rare earth intensifying screens? | gadolinium |
| what is one of the rare earth elements used for rare earth intensifying screens? | lanthanum |
| what is one of the rare earth elements used for rare earth intensifying screens? | yttrium |
| what is the safelights in the darkroom must be matched to the calcium tungstate or rare earth screens so that they will subtract out the color of light given off by the screens? | spectral matching |
| what is the relative speed of slow screen speeds? | 50 RS |
| what is the relative speed of par screen speeds? | 100 RS |
| what is the relative speed of high screen speeds? | 200-1200 RS |
| what anatomy is used with slow screen speed? | smaller extremities |
| what anatomy is used with par screen speed? | larger extremities |
| what anatomy is used with high screen speed? | abdomen |
| what is the purpose of an intensifying screen? | increase the efficiency of x-ray absorption and decrease patient dose |
| what does an intensifying screen convert a single photon into? | thousands of lower energy light |
| what happens to amount of radiation required to produce an acceptable image? | amount of radiation needed is reduced using intensifying screens |
| what percent of interactions in the IR are the result of the intensifying screen? | 99% comes from light conversion |
| what percent of interactions in the IR are produced directly by an x-ray photon? | 1% from direct interaction with x-rays |
| why is it important for the bases to be chemically inert and uniformly radiolucent? | chemically inert so that it will not react with the phosphor layer or interfere with the conversion of x-ray photons to light photons |
| why is it important for the bases to be chemically inert and uniformly radiolucent? | uniformly radiolucent to allow transmission of x-ray photons without causing artifacts to the image |
| what is a reflective materials? | titanium dioxide |
| what is the major function of the reflective layer? | reflects light back to film - allows for reduction of patient dose |
| why do some intensifying screens use dyes? | selectively absorb the diverging light photons that have a longer wavelength |
| what do the phosphor crystals convert? | incident x-ray photons into visible light photons |
| what is the main purpose of the protective coat? | limits the phosphor layer from abrasions and staining from use |
| what are white line artifact from? | scratches |
| what are primary characteristics of phosphor materials important to radiographs? | atomic number, conversion efficiency, luminescence |
| how many light photons are produced by each x-ray photon? | about 5,000 |
| what happens to radiation dose to patient as the conversion efficiency increases? | increased conversion efficiency, decreased patient dose |
| what does delayed phosphorescence create? | screen lag or afterglow |
| what does spectral matching refer to? | matching the wavelength, or color of the light from the screen, to the film sensitivity |
| what did Thomas Edison use to make the first intensifying screens? | calcium tungstate (CaWO4) |
| what color of light does the calcium tungstate crystals give off? | blue violet |
| tungstate crystals in converting x-ray energy into light? | 3-5% conversion efficiency |
| how efficient are the rare earth crystals in converting x-ray energy into light? | 15-20% conversion efficiency |
| what are the three types of screens? | detail or slow, medium or par speed, and high speed |
| how much will the calcium tungstate screens absorb? | 20-40% of the beam |
| how much will the rare earth screens absorb? | 50-60% of the beam (more efficient) |
| spatial resolution | minimum distance between two objects at which they can be recognized as two separate objects |
| 2 reflective materials | magnesium oxide and titanium dioxide |
| why do some intensifying screens use dyes? | it’s used in the reflective layer to selectively absorb this longer-wavelength light |
| what happens to the radiation dose to the patient as the conversion efficiency increases? | patient dose decreases |
Created by:
meechthebeech91
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