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29 Cards in this Set
- Front
- Back
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The active layer of the readiographic intensifying screen that emits light
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phosphor
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Examples of rare earths
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*gadolinium
*lanthanum *yttrium |
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Purpose of cassette with screens
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reduces radiation dose
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Intercepts light headed in other directions and redirects it to the film.
Increases the efficiency of the radiographic intensifying screen, nearly douling the number of light photons reaching the film. |
reflective layer
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Activates rare earths
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Turbian
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Any material that emits light in response to some outside stimulation.
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luminescent material/phosphor
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The emitted visible light from phosphor
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luminescence
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Two types of luminescence
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*fluorescence
*phosphorescence |
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When visible light is emitted only while the phophor is stimulated
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fluorescence
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When the phosphor continues to emit light after stimulation
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phosphorescence
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Undesirable phosphorescence in an intensifying screen
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screen lag/ afterglow
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Occurs when an outer-shell electron is raised to an excited state and returns to its ground state with the emission of a light photon.
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luminescence
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Three primary characteristics of radiographic intensifying screens
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*screen speed
*image noise *spatial resolution |
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A relative number that describes how efficiently x-rays are converted into usable light.
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screen speed
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The faster the screen speed, the _______ the resolution.
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lower
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Information concerning patient dose
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(IF)intensification factor
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IF equation
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Exposure required without screen / Exposure required with screens
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Screen speed is determined by
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*the # of xrays interacting with the phosphor
*how efficiently xray energy is converted to visible light that interacts with film |
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Radiographic conditions controlled by the radiologic technologist.
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*radiation quality
*image processing *temperature *film speed *screen speed |
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Two characteristics why rare earth screens have increased speed.
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*higher DQE
*higher CE |
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The percentage of x-rays absorbed by the screen.
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(DQE)Detective quantum efficiency
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The amount of light emitted for each e-ray absorbed.
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(CE)Conversion efficiency
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Calcium tungstate screen has a DQE of _____ and a CE of ____.
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20% and 5%
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Measured in a number of ways and can be given a numerical value.
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spatial resolution
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Screen blur is ________ in thinner screens.
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reduced
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Lead lines separated by interspaces of equal size.
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line-test pattern
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Reduction in spatial resolution is greater when phosphor layers are _____.
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thick
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Reduction is greater when crystal size is ______.
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large
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Screen-film contact can be checked by radiographing a ______. If there are any darker areas of blurring, screen-film contact is _____.
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wire mesh, poor
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