Flat panel detectors are a class of solid-state medical x-ray imaging devices similar in principle to the image sensors used in digital radiography and video, but due to the impracticability of focusing x-rays, the sensors are hundreds of times larger than those used in digital cameras.
X-rays pass through the subject being imaged and strike a scintillator layer of gadolinium oxysulfide or cesium iodide which converts the x-rays into light. Directly behind the scintillator layer is an amorphous silicon-on glass detector array manufactured using a process very similar to that used to make LCD televisions and computer monitors. Like an TFT-LCD display, millions of roughly 0.1 mm pixels each containing a thin-film transistor form a grid patterned in amorphous silicon on the glass substrate. Unlike an LCD, but similar to a digital camera's image sensor chip, each pixel also contains a photodiode which generates an electrical signal in proportion to the light produced by the portion of scintillator layer in front of the pixel. The signals from the photodiodes are amplified and encoded by additional electronics positioned at the edges or behind the sensor array in order to produce an accurate and sensitive digital representation of the x-ray image.
Flat-panel detectors are more sensitive, faster and cheaper than film. Their sensitivity allows a lower dose of radiation for a given picture quality than film. They are lighter, far more durable, smaller in volume, more accurate, and have much less image distortion than image intensification detectors and can also be produced in larger sizes.

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