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intensifying screens

QuestionAnswer
the principle action of the crystals found in intensifying screens is the conversion of x-rays into visible light CE
the process by which a crystalline material gives off visible light in response to x-radiation is termed luminescence
gadolinium and lanthanum are two common materials used in a new class of high speed screens rare earth phosphors
the effect of grainy appearance on radiographic image caused by quantum mottle is most commonly seen when extremely high speed imaging systems are used
the main reason that rare earth phosphors have all but replaced the older calcium tungstate phosphors in modern intensifying screens is their higher conversion efficiency
when all other factors remain unchanged an increase in the size of the crystals in the phosphor lay will not be associated with which of the following increase in the resolution of the imaging system
the speed of a film screen image receptor can be increased by making the following modification to the phosphor layer of the intensifying screens increase the thickness of the phosphor layer, add reflective backing to the phosphor layer
the primary advantage of the use of rare earth phosphors in modern film screen type image receptors is q the reduction in the exposure received by the patient the reduction in the exposure received by the patient
many of the phosphors employed in intensifying and fluoroscopic screens were first discovered by Thomas edison
the intensification factor for film screen imaging system can be determined by the formula intensification facto = exposure without screens/exposure with screens
which film holder image receptor is normally associated with the highest intensification factor the fastest speed
which of the following photoemissive chemicals is associated with the highest conversion efficiency gadolinium oxysulfide
the resolution of an intensifying screen can be improved by using light absorbing dyes in the phosphor layer
in order to obtain the maximum efficiency from a film screen image receptor the light emitted by the screens should correspond to the maximum light sensitivity of the film the process is termed spectral matching
The emission of light from a phosphor after the incident radiation exposure is terminated is called phosphorescence
the speed of a film screen image receptor can be increased by reflective backing behind each screen
the emission of light equal in all directions when phosphors are exposed to a stimulus is termed isotropic propagation
as the speed of a film screen imaging system increases 1. image resolution decreases 2. quantum mottle increases 3. noise increases 1,2,3
the amount of x-ray absorption by an intensifying screen phosphor is primarily dependent upon the photoelectric effect
a thin layer of lead foil is incorporated into the black lid of most cassettes to reduce the amount of backscatter that reaches the image receptor
the manufacturer of slow speed film screen imaging system may add a pink or yellow dye to the crystal layer to increase the recorded detail of the imaging system
which of the following phosphors is associated with the least sensitivity to x-rays with energies between 39-70 KeV phosphor number 2
the vertical lines seen at 39 KeV, 49 Kev, and 63 Kev are associated with the k-shell absorption edges of the phosphors
the grainy look or areas of uneven densities that may appear from the random distribution of x rays when a small amount of radiation reaches the image receptor is called Quantum mottle
reflection from successive underlying layers of luminescent crystals in slow intensifying screens can be lessened by adding a light absorbing dye to the phosphor layer
which of the following changes will not affect the speed of a film screen image receptor the barometric pressure
when a film screen image receptor is employed about what percentage of the x-ray films exposure is due to the light emitted by the phosphors in the screens 95-98%
the use of asymmetric front and back intensifying screens can result in images that have a wider latitude and higher contrast
the resolution ( resolving power of an intensifying screen) is generally measured in units of lines pairs per millimeter
the ratio of the x ray energy absorbed by a phosphor to the visible light energy emitted is termed conversion efficiency
the most common material used in older 100 speed film screen image receptor was the blue light emitting phosphor called calcium tungstate
the principle advantage the rare earth image receptor have over calcium tungstate screens is a greater speed without an appreciable loss of 1. optical density 2. radiographic contrast 3. spatial resolution 1,2,3
poor screens contact in a film screen imaging system or computed radiographic imaging system can be determined by using a wire mesh tester
the front of any type of film screen cassette or computed radiographic cassette holder must be covered by a light tight substance that is both homogeneous and radiolucent
in a film screen cassette the thin layer of foam rubber behind each intensifying screen serves to 1. increase speed of the image receptor 2. improve the contact between the film screen 3. decrease the amount of scattered radiation that reaches the film 2 only
rare earth phosphor intensifying s screen is to be manufactured with a thicker crystal layer this will 1. increase the speed of the image receptor 2. increase the resolving power of the screen 3. decease the inherent noise of the image receptor 1 only
the light emitted by a phosphor during its exposure to x radiation is termed fluorescence
a non screen image receptor requires a techniques of 200 mA 500 ms 75kVp if a 400 speed screen requires an exposure of 200 mA, 10 ms, 75 kip to give similar optical density what is the intensification factor for this exposure 50 times
Created by: Hstine86
 

 



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