What part of a digital detector element detects radiation?

• A. scintillation layer
• B. capture area
• C. TFT
• D. storage capacitor

Answer: (B)

The main idea is identifying the active, sensitive portion of a detector element—the part that actually responds to incoming X-rays and starts the signal that will be read out. In digital detectors, whether you’re looking at direct or indirect type, the detection happens in the capture area. This is the region that absorbs X-ray energy and converts it into charge (in direct systems) or into light that will be converted to charge by the photodiode. The scintillation layer is the separate layer that first converts X-rays to light in indirect detectors, but the signal that’s ultimately read out comes from the capture area. The thin-film transistor is the switch that transports the signal, and the storage capacitor holds the charge for readout. So the capture area is the part that directly detects the radiation and initiates the signal.