Which material is used in some direct digital detectors to convert X-ray energy into an electrical signal?

Which material is used in some direct digital detectors to convert X-ray energy into an electrical signal?

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

Answer: (D)

Direct digital detectors work by turning X-ray energy directly into an electrical charge without any light intermediary. Amorphous selenium does this effectively because it acts as a photoconductor: when X-rays are absorbed, electron-hole pairs are generated and collected by an applied electric field, producing a measurable electronic signal that forms the image. The other materials are used in indirect conversion or storage phosphor systems. Phosphor plates store energy in a phosphor layer and are read later by a laser (CR), while cesium iodide and gadolinium oxysulfide are scintillators that first convert X-rays to visible light, which is then detected by a photodiode or TFT array—not a direct electrical conversion.

Direct digital detectors work by turning X-ray energy directly into an electrical charge without any light intermediary. Amorphous selenium does this effectively because it acts as a photoconductor: when X-rays are absorbed, electron-hole pairs are generated and collected by an applied electric field, producing a measurable electronic signal that forms the image. The other materials are used in indirect conversion or storage phosphor systems. Phosphor plates store energy in a phosphor layer and are read later by a laser (CR), while cesium iodide and gadolinium oxysulfide are scintillators that first convert X-rays to visible light, which is then detected by a photodiode or TFT array—not a direct electrical conversion.