In digital radiography, what is the effect of using a lower dose on the signal-to-noise ratio and image quality?

• A. Lower dose decreases SNR, potentially decreasing image quality
• B. Lower dose increases SNR
• C. No effect on SNR
• D. Decreases contrast but not noise

Answer: (A)

Lowering the dose reduces the number of photons reaching the detector. Quantum fluctuations in photon arrival create noise, and with fewer photons these fluctuations become a larger fraction of the signal. Because the noise level scales with the square root of the detected signal, the signal-to-noise ratio falls as dose decreases. When SNR drops, the image looks grainier and fine details become less reliable, which degrades overall image quality. While digital systems can use post-processing and exposure adjustments to help, they can’t fully overcome the fundamental increase in noise that comes with a lower dose. That’s why using a lower dose tends to decrease SNR and potentially degrade image quality.