A Digital Imaging, Conventional Radiography (CR) x-ray unit is used to make the exposure. The CR system utilizes a Photostimulable Plate (PSP) and a plate reading unit in place of film and chemical processing. In general, the PSP is housed in a cassette that is very similar in appearance to a conventional radiographic cassette. This cassette can be used in a cassette tray in the table or wall cassette holder or may be used table top. The x-ray exposure is made in the same manner as with using a conventional F/S system. The next step is what differentiates CR imaging from S/C imaging. Instead of taking the cassette into a darkroom and processing a film, the PSP is placed in a CR reader. It is in the CR reader that the PSP is scanned by a laser beam. There are phosphors in the PSP that release light when scanned by the laser beam. This light is proportional to the energy of the x-ray beam that has stuck the PSP. This light is converted to an electrical signal by a photo-multiplier tube than converted to a digital signal via an A-D converter. At this point, the digital signal is sent to a Central Processing Unit (CPU) where image processing occurs. The image can now be displayed on a computer monitor.
One important concept with digital imaging is that an algorithm is applied to the “raw image”. This algorithm adjusts the “raw image” so that the contrast and density levels for examinations are consistent.
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