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the principle action of the crystals found in intensifying screens is the conversion of x-rays into visible light
the process in which a crystalline material gives off visible light in response to x-ray radiation is termed luminescence
gadolinium and lanthanum are two common materials used in a new class of high speed screens are called rare earth phosphors
the effect of grainy appearance in a radio graphic 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 screen is their high conversion efficiency
when all other factors remain unchanged, an increase in the size of the crystals in the phosphor layer will NOT be associated with which of the following decrease in recorded detail of the radio graphic image
the speed of a film- screen image receptor can be increased by 1. increase the thickness of the phosphor layer 2. add a reflective backing to the phosphor layer 3. add light absorbing dyes to the phosphor layer 1 & 3
the primary advantage of the use of rare earth phosphors in modern film-screen type image receptors is 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
which film-holder image receptor is normally associated with the highest intensification number? 400 film-screen image receptor
the resolution (recorded detail) 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 IR, the light emitted by the screens should correspond to the maximum light sensitivity to the film. This process is called 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 IR can be increased by a reflective backing behind each screen
emission of light equally in all directions isotropic
as the spread of a film-screen imaging system increases: 1. image resolution decreases 2. quantum mottled increases 3. noise increases All 3
the amount of x-ray absorption by an intensifying screen phosphor is primarily dependent upon the... photoelectric effect (remember almost 100%!!)
a thin layer of lead foil is incorporated into the back lid of most cassettes to reduce the amount of backs after that reaches the IR
the manufacturer of slow speed film-screen imaging system my add a pink or yellow dye to the crystal later to increase the recorded detail of the imaging system (slows down the speed; less speed =more detail)
the grainy look of areas of uneven densities that may appear from the random distribution of x-rays when a small amount of radiation reaches the IR is called? quantum mottle (due to low mA)
when a film-screen IR is employed, about what % of x-ray film's exposure is due to the light emitted by the phosphors in the screens? 95-98%
The use of asymmetric (different speed) front and back of 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 (lp/mm)
the ratio of the x-ray energy absorbed by a phosphor to the visible light energy emitted is: conversion efficiency
the most common material used in older 100 speed film-screen IR was blue light-emitting phosphor called calcium tungstate
the principle advantage that rare earth IR have over capsicum tungstate screens is a GREATER speed without the loss of 1. optical density 2. radiographic contrast 3. spatial resolution All 3
poor screen contact in a film-screen imaging system or CR imaging system can be determined by using a wire mesh tester
the front of any cassette holder must be covered by a light tight substance that is both homogenous and radiolucent
in a film-screen cassette, the thin layer of foam rubber (felt) behind each intensifying screen serves to: 1. increase speed of IR 2 improve contact between film screen 3. decrease the amount of scatter radiation that reaches the film 2 only
a rare earth phosphor intensifying screen is to be manufactured with a thicker crystal layer, this will: 1. increase speed of IR 2. increase resolving power of the screen 3. decrease inherent noise of the IR 1 only
the light emitted by a phosphor during its exposure to x-ray is fluorescence
Created by: lher