X-ray CT, X-rays, and mammography are used in place of conventional X-ray II (image intensifier) and IP (imaging plate). They have a wider dynamic range than II, which allows you to see images in real time without having to take out the plates and extract images like IP.

Regarding FPD, there are two types of indirect conversion and direct conversion.

Indirect type
The scintillator is laid flat, and the PD (photodiode) detects the light emission. No power supply is required.
Direct type
When a high voltage bias is applied to the selenium film and X-rays enter, the TFT transistor is turned on by the current flowing through it.
FPD structure

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