Which of the following would lead to an increase in patient dose?

• A. Increased detector element (DEL) size
• B. Decreased fill factor
• C. Decreased storage capacitor
• D. Decreased thin-film transistor (TFT) gate

Answer: (B)

Low fill factor means only a smaller portion of each detector pixel is sensitive to X-rays. With less of the pixel area converting photons into an electrical signal, the detector collects fewer photons for the same exposure, reducing signal and image quality. To achieve the same image quality, the exposure must be increased, which raises the dose to the patient.

Other factors influence dose differently. For example, larger detector element size can collect photons over a bigger area per pixel, which can improve efficiency and, depending on the imaging task, may allow a lower dose if you’re willing to accept reduced spatial resolution. Decreasing the storage capacitor or the TFT gate mainly impacts how much charge can be stored and transferred, which can degrade signal or introduce noise and may require higher exposure to compensate for the resulting image quality loss.