· Intensifying screens decrease the dose/ exposure to the patient but still afford proper film exposure
· Intensifying screen allows shortening of exposure times
· Luminescence = emission of light from a substance e.g. inorganic salt crystals (phosphors)
o Fluorescence = instantaneous emission (<10-8 sec)
o Phosphorescence = delayed emission (>10-8 sec)
· Base; Reflecting coat; Phosphor layer; Protective layer
· Screen and film spectra must match e.g. blue – green light emission spectrum must match film absorption spectrum of the film emulsion
· The efficiency of a screen of a screen to convert XR into light is the screens conversion efficiency :
o l = 12.4/ keV
· The ability of light emitted by the phosphor to escape from the screen and expose the film is the screen efficiency: See fig 6-7 BB: 152
· Diffusion of light in the screen affects the resolution - LSF
· The intensification factor is the ratio of the XR exposure needed to produce the same density on a film with and without the screen
o Increases with kVp
o Also filtering which increases the average beam kVp increases Intensification factor
· Speed (sensitivity/ efficiency) of screen:
o Thickness of screen (thicker increases absorption, but increases defusion)
o Size of crystals (increased absorption)
o Conversion efficiency (increase conversion efficiency – increase speed – rare earth crystals[gadolinium; europium])
o Higher absorption - rare earth crystals k-absorption matching
o Presence of light absorbing dye (decrease speed)
o Speedµ1/resolution (ability to record detail)
· Increase screen speed:
o Increased noise/ mottle – with phosphor with higher conversion efficiency
o No increase in noise/mottle – with increased phosphor thickness and higher absorption coefficient for x-rays
· Screen film contact:
o Light tight cassette
o Must have intimate contact with film (otherwise decrease resolution)
· Must be clean – dust creates unexposed points on film (high-spots)
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