Unlike the progressive digitization of CR, DR (Digital radiography), also called digital photography, early DR used a sensing screen plus an optical lens-coupled CCD (digitizing coupler) to acquire digitized X-ray images, with a slight resemblance to the workings of an image intensifier plus a CCD (see Fig. 1), and this technology is considered the first generation of DR technology.
Now commonly used DR is mainly the use of flat-panel detector port (FPD) on the X-ray image signals generated by scanning and direct readout, the imaging principle is the first X-ray signal into a visible light through the photoelectric 2 electrode composed of algal film layer (TFT) for the aggregation of the specialized readout circuit to send a direct read-out of the computer system to deal with the principle of work, see Figure II. At present, the flat detection port is divided into amorphous silicon (a: Si + CsI) as the representative of the indirect conversion digital photography (IDDR) and amorphous selenium (a: Se) as the representative of the direct conversion digital photography (DDR) two types. The working principle of the amorphous silicon (a:Si+CsI) indirect conversion digital photography plate is shown in Figure III.
The composition of DR generally includes a high-voltage generator port, X-ray bulb tube and bracket, plate detection port, system control port and other components. Compared with conventional X-ray compared to the signal, the advantages in addition to the advantages of CR, DR system is a flat panel detection of X-ray receiving device, replacing the traditional sensing screen and film, the realization of the digital X-ray signal, the dynamic range of the signal, the spatial resolution and high density resolution, the exposure agent to further reduce the inappropriateness of the price is more expensive.