Intensifying Screens
Amplify the incoming x-ray beam and reduces patient radiation dose.
Four Layers of Intensifying Screens
Base, Reflective Layer, Phosphor Layer, and Protective Coating
Base Layer
Is the furthest layer from the film usually polyester. Chemically inert so that it does not react with the other layers of the intensifying screen. 1millimeter thick, mechanical support for the active layer.
Reflective Layer
Located between the phosphor and the base. Made of shiny substance such as magnesium oxide or titanium dioxide. Nearly twice as much light is reflected toward the film. Improves efficiency of intensifier screen.
Phosphor Layer(Active Layer)
Contains phosphors that are capable of absorbing energy of an incident x-ray photon and the emitting light photons. Layers vary in thickness from 50- 300 ?m.
Protective Coating
The layer of the radiographic screen closest to the radiographic film. Helps eliminate the buildup of static electricity and is resistant to abrasions caused by handling.
Luminescence
Any material that emits light in response to some outside stimulation. The ability of material to emit light in response to excitation.
Two Types of Luminescence
Fluorescence, and Phosphorescence
Fluorescence
When visible light is emitted only when the phosphor is stimulated. Considered instantaneous emission.
Phosphorescence
Occurs when the phosphor continues to emit light after stimulation. Considered delayed emission and is referred to as "screen lag" or "after glow
Characteristics of Intensifying Screens
Resolution, Image Noise, Screen Speed
The most common screen resolution problem is caused by?
Poor Contact.
Image Noise
Appears on the radiograph as a speckled background.
Quantum Mottle
Principle component of noise. Is caused be an insufficient quantity of photons striking the intensifying screen making image aper grainy.
Screen Speed
Is a relative number that describes how efficient x-rays are converted into light by the intensifying screen.
Speed or Sensitivity of the intensifying screen is determined by:
Phosphor Composition, Size of phosphor Crystals, Phosphor Crystals, Phosphor thickness, Reflective layer, Dye, Concentration of phosphor crystals.
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