Difference between Amorphous Selenium and Amorphous Silicon Flat Panel Detector

Differences between amorphous selenium and amorphous silicon flat panel detectors;

1, the energy conversion mode is different.

Amorphous selenium belongs to direct conversion flat panel detector, and amorphous silicon belongs to indirect conversion flat panel detector.

2, the composition is different

Amorphous selenium flat panel detector is mainly composed of amorphous selenium layer TFT.

Amorphous silicon flat panel detector consists of scintillation crystal coating such as cesium iodide and thin film transistor or charge coupled device or complementary metal oxide semiconductor.

3, the working principle is different

The working principle of amorphous selenium flat panel detector is that the incident X-ray makes the selenium layer produce electron-hole pairs. Under the action of the applied bias electric field, the electron-hole pair moves in the opposite direction to form a current, which forms a storage charge in the thin film transistor.

The amount of charge stored in each transistor corresponds to the dose of incident X-rays, and the amount of charge at each point can be known through the readout circuit, and then the X-ray dose at each point can be known.

The working process of amorphous silicon flat panel detector is generally divided into two steps: first, the scintillation crystal coating converts X-ray energy into visible light; Secondly, TFT or CCD or CMOS converts visible light into electrical signals.

4. The spatial separation rate is different.

Amorphous selenium flat panel detector can obtain high spatial resolution, because amorphous selenium does not produce visible light and has no influence of scattering lines.

In this process, visible light will be scattered, which will affect the spatial resolution. Although the scintillator is processed into a column in the new process, the utilization rate of X-rays is improved and the scattering is reduced, but the influence of scattered light on spatial resolution cannot be completely eliminated.

Extended data

Flat panel detector is a kind of precise and expensive equipment, which plays a decisive role in imaging quality. Being familiar with the performance index of the detector is helpful to improve the imaging quality and reduce the X-ray radiation dose.

There are two main indexes to evaluate the imaging quality of flat panel detector: detection quantum efficiency (DQE) and spatial resolution.

DQ E determines the resolution of flat panel detector for different tissue density differences; Spatial resolution determines the ability to distinguish the fine structure of tissue.

The imaging ability of flat panel detector can be evaluated by investigating DQ E and spatial resolution.

In the indirect conversion flat panel detector, there are two main factors that affect DQE: the coating of scintillator and the transistor that converts visible light into electric signal.

In the direct conversion flat panel detector, the conversion of X-rays into electrical signals depends entirely on the electron-hole pairs generated by the amorphous selenium layer, and the energy level of DQ E depends on the ability of the amorphous selenium layer to generate charges.

Generally speaking, the limit DQE of indirect conversion flat panel detector with C sI +T FT structure is higher than that of a -Se direct conversion flat panel detector.

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