chapter 8 fosbinder
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| What type of radiation produces an image of body parts in direct exposure radiography? | transmitted and exit radiation
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| why does direct exposure radiography increase patient dose? | because without screens the total amount of energy exposing film is radiation
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| What does direct exposure film do to recorded detail? | increases it.
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| define- intensifying screens | Device found in cassettes that contain phosphors that convert x-rays in to light which then exposes film
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| What do the phosphors in intensifying screens do? | They are a chemical that emits light when struck by radiation.
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| what is the purpose of intensifying screens? | to decrease patient dose
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| What percentage of screens can be exposed by light and x-rays? | 90-99% light and 10% x-rays
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| What does an intensifying screen do to recorded detail? | decreases recorded detail
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| What are the 4 layers of the screen? | 1.protective layer (closest to film)
2.phosphor layer
3.reflecting or absorbing layer
4.base layer (farthest from film/closest to the cassette)
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| what is the base layer made of? | polyester plastic or cardboard
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| 3 characteristics of the base layer | 1.flexible and chemically stable and provides support/stability for phosphor layer.
2.chemically inert
3.radiolucent
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| Does a screen have both a reflective layer and an absorbing layer? | No. one or the other but not both.
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| What does the reflecting layer do? | It's used to reflect light back toward the film.
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| What does the absorbing layer do? | It consists of a light absorbing dye that absorbs low wavelength light photons directed toward the phosphor layer.
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| how does the reflective layer of the intensifying screen effect the efficiency of the screen? | increases efficiency
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| How does the reflective layer of the intensifying screen effect the overall recorded detail of the image? | decreases recorded detail
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| How does the absorbing layer of the intensifying screen affect the recorded detail of the image? | increases recorded detail
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| What is the phosphor layer known as? | The active layer
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| Why is the phosphor layer the most important screen component? | because it contains phosphor materials that absorb transmitted radiation and converts them to visible light.
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| What is the protective layer made of? | Plastics and protects fragile phosphor material beneath it.
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| What will happen if there is damage to the protective layer? | May result in the removal of underlying phosphors. This could create a negative density which causes a white area on the film.
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| Dirt/dust on the screen results in what type of negative density? | white dots/specks
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| the negative density of white lines on a film are the result of? | Scratches that result in loss of phosphors in that area of the screen.
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| What are the 3 characteristics of phosphor material? | 1.high atomic number
2.conversion efficiency
3.luminescence
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| Why is a high atomic number required for phosphor material? | to ensure interaction with x-ray photons
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| what is conversion efficiency? | Refers to the number of light photons that are generated for every x-ray photon.
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| What is luminescence? | The production of light from the phosphor upon interaction with a x-ray photon.
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| What are the 2 types of luminescence? | 1.fluorescence (good)
2.phosphorescence (bad)
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| What is fluorescence? | The desired type of luminescence. The ability of phosphors to instantaneously produce visible light when exposed to x-rays.then stops when exposure ceases.
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| What is phosphorescence? | When screen phosphors continue to emit light after x-ray exposure stops. known as screen lag/afterglow.
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| how does afterglow affect density on the image? | increases density
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| What is spectral emission? | Color of light emitted by a particular intensifying screen due to the phosphors used. Different phosphors will emit different colors when stimulated.
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| what is spectral sensitivity? | The color of light to which a particular film is most sensitive.
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| What type of film is sensitive to blue light? | panchromatic
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| What type of film is sensitive to green light? | orthrochromatic
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| What is spectral matching? | Correctly matching the color sensitivity of film to color emission of intensifying screens.
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| If a blue emitting intensifying screen is paired with orthochromatic film,what will occur to the image after exposure? | No image will be recorded
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| what is the chemical equation for calcium tungstate phosphors? | CaWO4
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| What color light does Calcium tungstate phosphors emit? | blue light
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| what % of x-rays are converted into light by calcium tungstate phosphors? | 3-5%
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| what % of x-rays are converted into light by rare earth screens? | 15-20%
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| what are the 3 types of rare earth screens? | 1.gadolinium
2.lanthanum
3.yttrium
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| What type of light does lanthanum and yttrium emit? | blue light
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| what type of light does gadolinium emit? | green light
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| What is the intensification factor? | Refers to a measurement of an intensification screen's ability to intensify the x-ray beam. It can also be used to determine how much patient dose is reduced.
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| what is screen speed/relative speed? | The ability of the intensifying screen to produce light and therefore produce light and therefore produce radiographic density.
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| what is the relationship between screen speed and recorded detail? | inverse-increased screen speed = decreased recorded detail
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| what are the 10 factors effecting screen speed? | 1.size of phosphor crystals
2.thickness of phosphor layer
3.materials used
4.distribution
5.kvp
6.temperature
7.presence of reflecting layer
8.light absorbing layer/dyes
9.absorption efficiency
10.conversion efficiency
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| what does the size of the phosphors do to recorded detail? | the larger the phosphor, the more divergence of light,therefore there is a decrease in recorded detail.
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| what does the thickness of the phosphor layer mean for screen speed? | The thicker the phosphor layer means that there are more phosphor crystals present= more efficient at producing light= increases screen speed
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| how does distribution of the phosphors effect the intensifying screen? | smaller phosphors and a more dense concentration limits the amount of divergence of light which will increase recorded detail.
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| how does kvp effect intensifying screens? | phosphors within the intensifying screens have high atomic numbers, therefore increasing kvp will increase light producing interaction with the phosphors.
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| what effect does temperature have on intensifying screens? | increasing temperature causes significant damage to the phosphors and will impede light production.
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| What does the reflecting layer in a screen do? | reflects light back toward film and increases speed of screen
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| what does the absorbing layer in a screen do? | absorbs light that would otherwise reach film and decreases speed of scree. which would increase recorded detail.
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| what is absorption efficiency? | the ability of the screen to absorb the incident photon.
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| increasing the atomic number of the phosphors in screens does what to absorption? | increases absorption of incident photons
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| what is the absorption percentage for rare earth? | 60%
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| what is the absorption percentage for calcium tungstate? | 30-40%
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| What is conversion efficiency? | refers to how well screen phosphors convert incident photons to light
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| what produces more light rare earth or calcium tungstate? | Rare earth because it produces 3-4 times more light
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| what does decreasing the thickness of the phosphor layer do to recorded detail? | increases recorded detail
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| what is the average fast screen speed? | 400SS
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| What is the average slow screen speed? | 100SS
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| What is the relationship between mAs and screen speed? | inversely related.
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| what is the mAs conversion formula? | mas1/mas2=SS2/SS1
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| What type of screens are AECs usually calibrated to work with? | generally fast screen speeds
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| what would happen if a detail screen was used with AEC? | Decreased density since AEC usually work with fast screen a when paired with a slow speed the image would come out under developed.
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| What is quantum mottle/image noise | when very low number of photons are used to produce image density, image appears mottled/blotchy.
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| how does increased screen speed affect quantum mottle and recorded detail? | increases quantum mottle and decreases recorded detail
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| what can you do to correct quantum mottle? | increase mAs while using a slower screen speed OR increase mAs and decrease kvp while using increased screen speed.
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| 5 qualities of the cassette/container for film and screen | 1.front is made of material with low atomic numbers to allow x-rays to pass
2.light proof
3.light weight
4. rigid/sturdy
5.promotes good film screen contact
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| what is used to test good film and screen contact? | wire mesh tool
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| what is the photographic formula? | PE= mA X time X kvp^2 X SS / SID^2 X GCF
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