Direct digital radiography
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Direct digital radiography (abbreviated as DR, DDR, or DX) is a type of digital radiography in which the digital registration of the image takes place directly at the detector with no intermediate processing step such as cassette readout in computed radiography (CR).
Direct digital radiography is often simply referred to as digital radiography, in which case computed radiography is regarded as a separate entity not included in digital radiography.
The word "direct" in direct digital radiology refers to the direct image registration in the detector, without the need for an intermediate cassette as in computed radiography. It should not be confused with the distinction between direct (x-rays to electrical charge) and indirect (x-rays to visible light through a scintillator, then visible light to electrical charge) conversion taking place inside the detector 1.
Flat panel detectors (FPDs)
These are the most common detectors used in direct digital radiography. For more details see the main article on flat panel detectors. There are two primary methods of converting the x-rays into charges, either indirect or direct.
Indirect conversion is so named because this technique still uses a scintillator to convert x-rays to visible light before conversion from visible light to an electrical charge for subsequent readout.
Direct conversion is so named because this technique directly converts the x-rays into proportionally sized electrical charges with no intermediate scintillating step.
Charge-coupled device (CCD) and complementary metal–oxide–semiconductor (CMOS) detectors are alternatives to flat panel detectors. They require a scintillator (indirect conversion method). Their implementation is limited due to restricted size of the detectors 1,4.