Which of the following measures the efficiency of a system to convert the X-ray input signal into a useful output image?

• A. DQE
• B. MTF
• C. SNR
• D. Noise

Answer: (A)

The efficiency of converting the X-ray input signal into a useful image is captured by detective quantum efficiency (DQE). DQE describes how much of the incoming signal’s information actually appears in the final image, accounting for how the system handles noise and resolution. It is defined as the ratio of the squared output signal-to-noise ratio to the squared input signal-to-noise ratio at a given spatial frequency, often incorporating the system’s modulation transfer function and noise characteristics. A higher DQE means you get more image information for the same radiation dose, or the same image quality with less dose.

MTF focuses on how well the system preserves contrast across spatial frequencies (resolution), not on overall signal efficiency. SNR measures the amount of signal relative to noise in the output but doesn’t describe how effectively input information is transferred through the system. Noise describes random fluctuations themselves, without indicating how much of the input signal is preserved in the final image.