Intensifying screen

Intensifying screen is used in the cassette to intensify the effect of the X-ray photon by producing a larger number of light photons. It decreases the mAs required to produce a particular density and hence decreases the patient dose significantly. In cassettes, which use double emulsion films, two screens are used, mounted on both sides of the cassette. In mammography, however, a single screen on the back side and a single emulsion film is used.

The thickness of an intensifying screen is about 0.4 mm.

Layers 
  • base
  • reflecting layer/absorptive layer
  • phosphor: absorbs the X-ray photon and convert it to visible light that is recorded by the film
    • calcium tungstate (CaWO4): blue light
    • lanthanum oxybromide (LaOBr): blue light
    • gadolinium oxysulfide (Gd2O2S): green light
  • protective layer

Rare earth elements are used in present day screens as they are faster and have higher absorption and conversion efficiency:

  • gadolinium
  • lanthanum
  • yttrium
Spectral matching

It is important to note that the color of the light emitted (wavelength) must match the light sensitivity of the film used. This is known as spectral matching:

  • conventional films: sensitive to ultraviolet and blue lights
  • orthochromatic films: sensitive to ultraviolet, blue and green lights
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Article Information

rID: 30319
Section: Physics
Tag: refs
Synonyms or Alternate Spellings:
  • Intensifying screens

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