Which term describes the fraction of incident photons that are absorbed by the detector?

• A. Capture efficiency
• B. Quantum mottle
• C. Spatial resolution
• D. Quantization

Answer: (A)

Capture efficiency is the fraction of incident photons absorbed by the detector and converted into a usable signal. In x‑ray imaging, not every photon contributes to the image: some pass through, and some scatter away. Only photons that are absorbed produce the charge or light that the detector reads as part of the image. So higher capture efficiency means more of the incoming energy is detected, improving image signal without needing more dose. This concept helps explain why the detector’s ability to absorb photons directly affects image quality and dose efficiency. The other terms refer to different aspects: quantum mottle is noise from too few photons, spatial resolution is how well small details are distinguished, and quantization is the digital conversion of analog signal into discrete levels.