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Week 4b Chapter 15 Intensifying Screens

Week 4b Chapter 15 Intensifying Screens - Chapter 15...

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Chapter 15 Radiographic Intensifying Screens And Cassettes There are three key parts of the Image Receptor for Conventional Radiography: Film to record the image Intensifying Screens to expose the film Cassette to protect the screens and film
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Radiographic Intensifying Screens Less than 1% of the incident x-rays interact with the film to contribute to the latent image. The intensifying screens converts the remnant radiation to light than produces the latent image. They act as an amplifier of the remnant radiation.
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Radiographic Intensifying Screens About 30% of the x-rays striking the screens interact with the screens producing a large number of visible light photons. The use of intensifying screens results in considerable lower radiation dose to the patient but has the disadvantage of causing a slight blurring of the image.
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Radiographic Intensifying Screens Most conventional radiographic cassettes have a pair of screens that sandwich the film. This design used double emulsion film.
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Screen Construction Four Distinct Layers Protective Coating Phosphor Reflective layer Base
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Protective Coating Coating is transparent to light. Resistant to abrasion and damage from handling. Resistant to static electricity Provide a surface for cleaning while protecting the phosphors.
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Phosphors The active layer of the screen is the phosphors. The phosphors emit light when stimulated by x-rays. Prior to 1970 the most common phosphor was a crystalline form of Calcium Tungstate.
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Phosphors Modern screens use rare earth elements such as: Gadolinium Lanthanum Yttrium
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Properties of Phosphors used in Intensifying Screens High atomic number so x-ray absorption will be high. Quantum Detective Efficiency Emit a large amount of light per x-ray absorption. Conversion Efficiency Light must be of proper wavelength to match the sensitivity of the film Spectral Matching
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Properties of Phosphors used in Intensifying Screens Phosphor Afterglow should be minimal. Phosphor should not be affected by heat humidity or other environmental conditions
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Influences of the Action of Intensifying Screens Thickness of the phosphor Layer Concentration of the crystals Size of the crystals.
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Reflective Layer The light from the phosphors is emitted isotropically. Without a reflective layer, only half of the light would interact with the film.
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