In direct-conversion detectors using amorphous selenium, which statement about conversion is true?

• A. X-ray photons are converted directly into an electrical signal
• B. The detector uses a scintillator to convert X-rays to light
• C. The readout is achieved by a separate image plate
• D. The device requires a photomultiplier tube

Answer: (A)

Direct-conversion detectors with amorphous selenium work by turning X-ray photons straight into electrical charge. When X-rays are absorbed in the selenium layer, electron-hole pairs are created and, under an applied electric field, these charges are collected by the detector electrodes to form an electrical signal that can be read out by the surrounding circuitry. This approach avoids any intermediate light production, which is why it can achieve high spatial resolution—the signal comes directly from the X-ray interaction, not from light spreading through a scintillator.

If X-rays were first converted to light in a scintillator, that would describe indirect conversion, which is not the case here. Using a separate image plate is a characteristic of computed radiography, not direct-conversion flat-panel detectors. Relying on a photomultiplier tube would involve detecting light, not the direct electrical signal produced by charge generated in amorphous selenium.