Screen/Film Image Receptor Systems
3 functions: protect the film from exposure to light during use, protects the delicate film from bending and scratching during use, and contain intensifying screens and keep them in close contact with the film during exposure Exposure side of cassette is the front; contains ID blocker that is protected from radiation in that area; ID reserves as area for printing patient information at time of processing The cassette back is the access side of the cassette; this side faces up; this side places ID blocker in the upper left corner Front is made of radiolucent material (easily penetrated by the x-ray beam); may be very lightweight metal alloy or plastic material made of durable resin. Inside of cassette front is the front intensifying screen
Back of cassette: made of metal or plastic, inside the back is a layer of lead foil (prevents backscatter); backscatter causes fog on film if not absorbed by foil layer Inside foil layer is padding (keeps intensifying screens pressed tightly against the film when the cassette is closed) maintain good film contact Back intensifying screen is on the padding; covers inside surfaces of the cassette; film is placed between the intensifying screens Special cassettes use phototiming systems; must allow remnant radiation to pass readily through the cassette back to the detector; they have radiolucent back and no lead foil layer; clearly marked “phototiming cassette” and should be used only for this purpose
Intensifying screen is a flat surface coated with fluorescent crystal called phosphors (give off light when exposed x-rays called fluorescence) Phosphors absorb x-ray energy and emit the energy in the form of light Direct x-rays expose the film to some degree but the greatest amount is from the light of intensifying screens Over 99% of x-ray image is formed by screen light
Purpose of intensifying screen is to reduce the amount of exposure...
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