Amorphous selenium is a material used in which imaging system?

• A. Computed Radiography (CR)
• B. Direct Digital Radiography (DR)
• C. Radiographic film
• D. Indirect Digital Radiography (DR)

Answer: (B)

Amorphous selenium is used in direct digital radiography because it acts as a photoconductor that directly converts x-ray energy into an electrical signal, without any light intermediary. In a direct DR detector, a-Se sits above a thin-film transistor (TFT) array. When x-rays hit the a-Se layer, they generate electron-hole pairs, and an applied electric field collects these charges to produce a digital signal that is read out by the TFTs. This direct conversion preserves high spatial resolution and minimizes signal spread that light diffusion would cause.

This approach contrasts with indirect DR systems, which rely on a scintillator to first convert x-rays into light, and then a photodetector (often amorphous silicon) to turn that light into an electrical signal. Radiographic film is traditional analog, and CR uses photostimulable phosphor plates rather than a-Se.