In a flat-panel detector, which component is used to read out the signal from the detector array (acts as the switching matrix)?

• A. Analog-to-Digital Converter (ADC)
• B. Photodiode
• C. Charged-Coupled Device (CCD)
• D. Thin-Film Transistor (TFT) Array

Answer: (D)

Reading out the signal from a flat-panel detector relies on a grid of thin-film transistors at each pixel. These transistors form the switching matrix that selectively addresses rows and columns, allowing the charge collected by the photodiode at each pixel to be moved onto data lines one by one. This row/column addressing enables the entire detector array to be scanned and its signals read in a controlled sequence. The photodiode is the light-detecting element that converts scintillator-produced light into charge, but it’s the TFT array that provides the necessary switching and readout path. After the charge is read, an analog-to-digital converter turns the analog signal into digital data. The CCD is a different technology that uses charge-transfer mechanisms, but in typical flat-panel detectors the TFT array serves as the readout switching matrix.