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Computed radiography (CR) is the use of photostimulable phosphor as an image receptor. The image receptor is held in a similar casing (cassette) to that of the traditional film screen. Computed radiography harnesses the absorption of radiation, trapping electrons at energy levels via the process of photostimulable luminescence.
CR enables the transition of conventional radiography to digital radiography, by using existing x-ray equipments for conventional radiography 3.
The computed radiography plate has a thin layer of phosphor grains, known as a photostimulable phosphor. The plate is exposed to x-ray radiation exciting the phosphor, exciting the electrons to be trapped in the lattice until inevitably they are stimulated by the second round of illumination.
Analog to digital conversion
The computed radiography plate is exposed to a small, high-intensity laser resulting in the previously trapped electrons to return to their respective valence bands, letting off violet light.
A photomultiplier tube will interpret this light and convert it into an electric signal that, via an analog-to-digital converter (ADC) is digitized and mapped onto a pixel matrix.
Using a white light, the computed radiography plate can be 'reset', thus they can be reused repeatedly if carefully handled.
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- 2. Arnulf Oppelt. Imaging Systems for Medical Diagnostics: Fundamentals, Technical Solutions and Applications for Systems Applying Ionizing Radiation, Nuclear Magnetic Resonance and Ultrasound. (2006) ISBN: 9783895782268
- 3. Allisy-Roberts P & Williams J. Digital Radiography. Farr's Physics for Medical Imaging. 2008;:79-90. doi:10.1016/b978-0-7020-2844-1.50009-0