Which material is used in direct conversion DR detectors?

• A. Cesium Iodide
• B. Amorphous Selenium
• C. Sodium Iodide
• D. Gadolinium Oxysulfide

Answer: (B)

Direct conversion DR detectors rely on a photoconductive layer that directly turns X-ray energy into electrical charges, which are collected to form the image. Amorphous selenium fits this role because when X-rays hit the a‑Se layer under an applied electric field, they generate electron-hole pairs that are swept to electrodes, producing a signal proportional to the exposure. This direct conversion avoids any intermediate light emission, giving higher spatial resolution and seamless integration with a TFT array in a flat-panel detector. The other materials listed are scintillators used in indirect conversion detectors: they convert X-rays to visible light first, and that light is then detected by a photodiode or transistor, which can blur fine detail.