Intensifying Screens

Question Answer
When was the first screen made? 1896
What was the first screen made out of Calcium tunsgtate
What other things were used for the first screens? Sheelite, barium lead sulphate, zinc sulphate
Disadvantages in the first intensifying screens? Lag, graininess due to large crystals & impurities
In the 1970s, rare earth phospors began with gadolinium,lanthanum,yttrium, and didnt have Lag, and less impurities
Purpose of intensifying screens Convert xray energy to light energy, Reduce patient exposure, Increase radiography contrast(shades of gray)
How much of the exposure on the film is due to light emighted from screens 90-99% 10% or less of the exposure is the result of the xrays
Phosphor Fluorescent material that absorbs xray energy and converts it to a specific spectrum of visible light
Emission spectrum Wavelength and color of light emitted by the phosphor
Luminescence Emission of visible light when struck by xray
Fluorescence Preferred Light emission ceases within 10^-8 seconds after xray exposure
Phosphorescence Afterglow or screen lagContinued emission of light after 10^-8 seconds after xray exposure
Base layer Lauer farthest from the film
Rugged yet flexible layer Base layer
1 mm thick Base layer
Cardboard, polyester, aluminum Base layer
Chemically inert-no reactions to phosphprs or photonsContains no impurities Must not become damages by radiationMust not discolor with age Base layer
25 mm thickMagnesium oxide & titanium dioxideDirects light toward the filmIncreases speed; decreases resolution Reflective layer
Active layer Phosphor layer
Converts xray energy to light energy, 150-300 mm thick,,rare earth or non rare earth used,High atomic # to increase xray absorption Phosphor layer(active layer)
What is conversion efficiency How efficiently phosphors convert xrays to light.
What is intensification factor? Measures the speed of the screen.Can be used to determine dose reduction
What is resolution? The ability to produce an acurate,clear image, measured by pairs/mm (LP/mm)
The exposure without screens is ____ than with screens. 30 times greater
Factors that affect intensification factor Phosphor composition ThicknessReflective layerDyeCrystal sizeConcentration
Phosphor composition Have high atomic numberExamples rare earth and non rare earthTypes determine the efficiency of xray conversion
Non rare earth 4-5% conversion efficiency Blue violet spectrum Ex. Calcium tunsgstate,barium stronttiumsulfite, barium fluorochloride
Rare earth phosphors 15-25% conversion efficiency Blue green spectrum, blue or green
Have a high QDE -Quantum detection efficiency-ability to interact with xrays Rare earth phosphors
The thicker the phosphor layer The more xrays will be absorbed
The thinner the phosphor layer The less xrays will be absorbed
The thicker the phosphor layer The more phosphor crystals present
The thinner the phosphor layer The less phosphor crystals present
The thicker the phosphor layer More xrays are converted to light
Increased thickness in phosphor layer- Increased speed–decreased resolution
Increases speed,decreases detail, decreases patient dose Reflective layer
Isotropically Phosphor emit lights any direction
True or false. Some phosphors are so efficient at converting xray energy to light the reflective layer is not needed. True
What layer is dye added to to balance detail when using fast speed screens? Phosphor layer
Would these be from large or small crystal sizes? More xray absorption More light emittedIncreased divergenceIncreased speedIncreased graininess Decreases resolution/detail Large
Small or large crystal size??Less light emittedDecrease speedIncrease resolution/detail Small
As temperatures increase- Speed decreases.
Increase speeed Decrease detail
True or false. Kvp directly proportional to speed True Greatest absorption of xray occurs when photon energy and kshell BINDING energy are almost the same
What is the type of interaction that takes place almost 100% of the time ? Photoelectric interaction on the inner shell which creates characteristic radiation
Whuch way is film classified? Descriptive and numericalDetail;slow, medium;par, high;fast, rare earth; Numerical 25-1200

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