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What IS Digital X-Ray

Computed radiography, like film–screen radiography, has the disadvantage that the production of the final image involves removing the cassette from the X-ray set, taking the plate to a reader, and waiting for a period of about 1 min while the film is processed or the CR plate is scanned. Although the delay time is not great and the distance between X-ray equipment and CR reader may be short, this may be inconvenient and may limit patient throughput. DR systems use imaging devices that remain in situ and produce an image with a delay that is generally no more than about 10 s.

The distinction between computed and digital radiography is somewhat artificial, because both are digital technologies employing computers for their implementation. There are CR systems (i.e. systems that use photostimulable phosphors) that incorporate the plate reader into the X-ray equipment so that for the operator there is little difference between the two. DR itself is divided into two main classes: indirect DR and direct DR (often referred to as DDR).

The most common DR detectors are based on amorphous siliconthin-film transistor (TFT) arrays, the dimensions of the array being the size of the area to be imaged. A transistor is a device that amplifies an electrical signal, and in the TFT array the amplified signal is stored as an electrical charge. The charge can be released by applying a high potential. In the TFT array, which is essentially a large integrated circuit, each row of detectors is connected to the activating potential and each column to a charge-measuring device. The potential is applied row by row, so that the timing of the detected signal determines the position of the pixel from which it originated.

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