FPDs are digital image detectors, also known as flat panel detectors, divided into amorphous selenium FPDs and amorphous silicon FPDs. amorphous selenium FPDs are similar to radiographic film dark boxes and are electronic dark boxes that can directly convert incident X-ray energy into digital signals, so they are also called direct conversion FPDs; amorphous silicon FPDs are also similar to X-ray film dark boxes and can receive X-rays before converting them into digital signals. FPDs have strong density resolution and are suitable for situations requiring high density resolution, which is beneficial for accurate diagnosis.