X-ray photons are absorbed into a phosphor crystal giving rise to a high energy photoelectron. The plate is a layer of phosphor crystals (made of barium fluorohalide activated with divalent europium ions (BaFX:Eu)) embedded in a polymer binder with the top surface protected by a layer of toughened plastic. It allows x-ray energy to be temporarily stored in a phosphor screen to be read-out later. X-ray phosphorescence: this is when the emission of light is delayed over a timescale of many minutes, hours or days and can be accelerated by shining specific coloured light onto the phosphor.This is the mechanism that predominates in screen film radiography X-ray fluorescence: the immediate emission of light.It involves two mechanisms that both occur to some degree when a phosphor screen is irradiated: X-ray luminescence is the physical mechanism by which x-ray energy is converted into light in a phosphor screen. It is then read out by TFT switches pixel by pixel. The positive charge is attracted to a charge capacitor that stores the latent image. Direct DR: x-ray photons act directly on a photoconductor layer producing positive and negative charge.Indirect DR: x-ray photons hit a scintillator layer, which then releases light photons that then hit an active matrix array that digitises the signal. The x-rays hit a permanently placed set of hardware, which then sends the digital information directly to a readout mechanism. With digital radiography no cassettes are used. The cassette is then placed into a reader with a laser shone on to it which releases the stored photons, collects the signal, and digitises it to be displayed on a display screen. When the x-rays hit they form a latent image in the phosphor. There are two different techniques: computed radiography and digital radiography.Ĭassettes are used that have a phosphor screen. These have now been replaced by digital radiography. Originally, screen-film radiography (SFR) was used in which a physical copy of the x-ray film was produced.
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