Digital radiography flat-panel systems with integrated readout mechanisms were
introduced in the market by the end of the 1990s [19]. Flat-panel systems, also
known as large-area X-ray detectors, integrate an X-ray-sensitive layer and an
electronic readable system based on TFT arrays. Detectors using a scintillator
layer and a light-sensitive TFT photodiode are called indirect-conversion TFT
detectors. Those using an X-ray-sensitive photoconductor layer and a TFT charge
collector are called direct-conversion TFT detectors [19]. The reference to amorphous
silicon (a-Si), which is used in TFT arrays to record the electronic signal,
should not be confused with a-Se, the material used to capture X-ray energy in a
direct digital detector. The structure of a DR flat-panel system is shown in Fig. 2.4.
This electronic readable system allows an active readout process, also called
active matrix readout, in opposition to the storage phosphor systems where no
active readout elements are integrated within the detector. The entire readout
process is very fast, allowing further developments in digital real-time X-ray
detectors