The DR system, that is, the direct digital X-ray photography system, is composed of an electronic cassette, a scanning controller, a system controller, an image monitor, etc. It directly converts X-ray photons into digital images through the electronic cassette. Image is a direct digital X-ray photography in a broad sense. In a narrow sense, direct digital photography is DDR (DirectDigit Radiography), which usually refers to digital radiography that uses flat-panel detector image direct conversion technology. It is a true direct digital X-ray photography system. According to the detector type, it is mainly divided into amorphous silicon flat panel DR (mainstream), amorphous selenium flat panel DR and CCD DR (mainstream); according to the frame structure, it is divided into suspension DR and column (UC arm) DR;