Flat-panel detector systems typically use a thin-film transistor (TFT). This device functions to:

• A. Convert x-rays into light
• B. Convert light into electrons
• C. Collect electrical charge
• D. Convert electrical change into a digital signal

Answer: (C)

In flat-panel detectors, the thin-film transistor (TFT) acts as a per-pixel switch that collects and routes the electrical charge generated at that pixel. During exposure, each pixel’s photodetector (such as a photodiode or the scintillator’s light-to-electron conversion) creates charge that is stored on a small capacitor. The TFT then enables that stored charge to be read out by the detector’s data bus and ultimately converted to a digital value. So, the primary function of the TFT is to collect electrical charge and connect it to the readout electronics. It does not convert x-rays to light, nor light to electrons, nor directly digitize the signal—those roles belong to the scintillator/photodiode and the ADC/readout circuitry, respectively.