direct detection DR system
The Direct Detection Flat Panel System uses an X-ray photoconductor material such as amorphous selenium (a-Se), which directly converts x-rays into visible light.
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| Direct Detection |
In the Direct Detection Flat Panel System, no scintillation material is used as indirect detection, which converts xrays into light. In this, because selenium is used in amorphous form, its large plate can be easily made by vapor deposit, which is a cost effective and reproducible technology.
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| Flat pannel system |
Selenium's atomic number (Z = 34) is slightly less than normal, so its thickness is kept relatively high (about 1mm). It has good x-ray detection property and its spatial resolution is also high.
Selenium is a photoconductor that is exposed to x-ray, so its electrical conductivity changes. This altered electrical conductivity is proportional to x-ray intensity. An electrical field is placed between the two surfaces of the selenium layer, reducing the lateral deffusion of the produce electrons as they move towards the thin film transistor (TFT).
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| ADC direct conversion |
When this detector is exposed by X-ray, there are electron emits in the selenium layer, which discharge some part of the charged voltage. This voltage discharge is proportional to the radiation intensity, creating a letent charge image. This charge is stored in the capacitor, and this charge pattern is readout by the scan control line as an indirect detection system. Finally, the signal is digitized for image analysis.
Selenium is highly susceptible to changes in humidity and temperature, so it needs protection from the environment.
