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