Flat Panel Detector Knowledge
In digital radiography, X-ray energy is converted into electrical signal by flat panel detector.Therefore, the characteristics of flat panel detector will have a greater impact on DR image quality.The choice of flat panel detector must be considered when selecting DR. The performance index of flat-panel detector will have a great impact on the image, and the hospital should also choose its own flat-panel detector according to the actual needs.
DR flat panel detector can be divided into two types: amorphous selenium flat panel detector and amorphous silicon flat panel detector. In terms of energy conversion mode, the former belongs to direct conversion flat panel detector, and the latter belongs to indirect conversion flat panel detector.
The amorphous selenium flat panel detector is mainly composed of amorphous selenium layer TFT. The incident X-ray makes the selenium layer produce electron hole pairs. Under the action of the applied bias electric field, the electron and hole pair move in the opposite direction to form a current, which forms a storage charge in the thin film transistor. The stored charge of each transistor corresponds to the dose of incident X-ray. 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. Because amorphous selenium does not produce visible light and has no effect of scattering lines, it can obtain high spatial resolution.
The amorphous silicon flat panel detector is composed of a scintillation crystal coating such as cesium iodide and a thin-film transistor. Its working process is generally divided into two steps: first, the scintillation crystal coating converts X-ray energy into visible light; second, TFT or CCD converts visible light into electrical signal. Due to the scattering of visible light in this process, the spatial resolution will be affected. Although the scintillation crystal is processed into columnar shape to improve the utilization of X-ray and reduce the scattering, the influence of scattered light on spatial resolution cannot be completely eliminated.
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