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Comparison of direct and indirect conversion techniques

1. Indirect conversion technology
Due to the crystal structure, the Csl scintillator layer inevitably has light scattering at the same time as the signal is transmitted, and the absorption rate is decreased, which has a slight influence on the image quality but is not serious.
Indirect conversion has high quantum detection performance, which can obtain high quality images under low dose X-ray exposure. In addition, its imaging speed is fast, and the fields of fluoroscopy and time subtraction increase the range of X-ray use.

2. Direct conversion technology
Selenium can be used as a photoconductor to directly convert an optical signal into an electrical signal to avoid scattering. Compared with indirect conversion technology, direct conversion has low X-ray absorptivity, and image quality is not well guaranteed under low dose conditions. Selenium is sensitive to temperature and its use conditions are limited.

From the perspective of spatial resolution, amorphous selenium plates exhibit better resolution than amorphous silicon plates. According to the measured data, the resolution of the direct conversion technology can reach 3.8Lp/mm on average, and the average resolution of the indirect conversion is about 3.0Lp/mm.

From the perspective of exposure dose, the amorphous silicon plate has a high quantum detection efficiency, so its exposure dose is significantly lower than that of the amorphous selenium plate under the same conditions, which is basically 1/2 of the latter. Therefore, from the dose angle Consider that indirect conversion technology has advantages.

From the perspective of imaging speed, amorphous selenium plates are imaged more rapidly than amorphous silicon plates. Only one point determines that flat panel detectors used as perspectives use indirect conversion techniques.