H F INTENSIFYING SCREENS
Quiz yourself by thinking what should be in
each of the black spaces below before clicking
on it to display the answer.
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| What % of the x-rays incident on the radiographic film interact with the film | Less than 1%
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| Use of screens results in a _____ radiation dose to the patient but there may be a slight _______ to the film | lower/ blur
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| Visible light interacts with the film to form | latent image
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| Any material that emits light in response to some outside stimulus | luminescent material or a phosphor
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| 2 types of luminescence | 1. Fluorescence 2. Phosphorescence
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| Radiographic intensifying screens convert x-ray energy to | visible light
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| visible light is emitted only when stimulated | Fluorescence
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| the phosphor continues to emit light after stimulated | Phosphorescence
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| the phosphor continues to emit light after stimulated | screen lag or after glow
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| relative number used to identify the efficiency of conversion of x-rays to visible light | Screen speed
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| emits light during stimulation | phosphor
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| phosphor used before 1980 | calcium tungstate
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| rare earth phosphors | gadolinium, lanthanum, and yttrium
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| Can produce more light with less exposure | Rare earth screens
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| faster than calcium tungstate screens | Rare earth screens
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| reflects the light that is going in the opposite direction and directs it to the film | reflective layer
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| This is the thickest layer | base
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| This layer is primarily for mechanical support | base
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| Light photons are produced | isotropically
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| amaount of photons are emitted in the direction of the film | Less than 1/2
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| the speed of the screens are influenced by | The thickness of the phosphor layer and the size of the crystals
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| This layer helps to resist abrasion and damage | Protective coating
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| This layer also helps to decrease static electricity on the screen | Protective coating
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| layer that is closest to the film | Protective coating
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| what are the layers of the screen | 1. Protective coating 2. Phosphor 3. Reflective layer 4. Base
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| Two reasons to limit the size of the x-ray field: | to decrease unnecessary exposure and Decrease scatter radiation so that image contrast improves
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| X-rays that enter the image receptor | image forming x-rays
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| X-rays that exit the patient | remnant x-rays
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| The simplest beam restricting device | Aperture diaphragms
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| positive beam limiting devices | Automatic collimators
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| the most common beam limiting devices for radiography | Variable aperture collimators
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| Has a white light and mirror to show the field and the central ray | Collimators
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| These are metal structures that extend from the x-ray tube and restrict the useful beam to the required size | Cones and cylinders
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| Consists of 2 sets of adjustable lead shutters that provided a rectangular or square field | Collimators
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| used to decrease the patient dose | Screens
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| the way to determine how efficient the screens are at reducing the dose | The intensification factor
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| IF = | Exposure without a screen / Exposure with a screen
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| refers to how small an object can be to be identified on an image | Spatial resolution
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| refers to the ability to distinguish between and image tissues of similar density | Contrast resolution
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| Speckled background and is seen with fast screens | Image Noise
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| Quantum mottle | Image Noise
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| Screen speed categories | Par, High speed, Fine detail
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| rare earth – 50 to 80 speed | Fine detail
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| High spatial resolution | Fine detail
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| rare earth – up to 1200 speed | High speed
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| Most use from 400-600 | High speed
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| Calcium tungstate – 100 speed | Par
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| % of the x-rays striking the radiographic screens interact with the screen | 30
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| involves the outer shell electrons | Luminescence
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Created by:
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