DR flat panel detectors can be divided into two types: amorphous selenium flat panel detectors and amorphous silicon flat panel detectors. From the perspective of energy conversion, the former belongs to direct conversion flat panel detectors, and the latter belongs to indirect conversion flat panel detectors.
The amorphous selenium flat panel detector is mainly composed of an amorphous selenium layer TFT. The incident X-rays make the selenium layer generate electron-hole pairs. Under the action of an externally biased electric field, the electrons and holes move in opposite directions to form a current, and the current forms a stored charge in the thin film transistor. The amount of stored charge of each transistor corresponds to the dose of incident X-rays, and the charge amount of each point can be known through the readout circuit, and then the X-ray dose of each point can be known. Since amorphous selenium does not produce visible light and has no influence of scattered rays, a relatively high spatial resolution can be obtained.
The amorphous silicon flat panel detector is composed of a scintillation crystal coating such as cesium iodide and a thin film transistor or a charge-coupled device or a complementary metal oxide semiconductor. Its working process is generally divided into two steps. First, the scintillation crystal coating measures the X-ray energy Converted into visible light; secondly, TFT or CCD, or CMOS converts visible light into electrical signals. Since visible light will scatter during this process, it will have a certain impact on the spatial resolution. Although the scintillator is processed into a columnar shape in the new process to improve the utilization of X-rays and reduce scattering, the influence of scattered light on the spatial resolution cannot be completely eliminated.