Low mAs in radiography typically results in which type of image degradation?

• A. Fog
• B. Increased sharpness
• C. Increased contrast
• D. Quantum noise

Answer: (D)

Low mAs reduces the number of x-ray photons reaching the detector. When the signal is built from relatively few photons, the random fluctuations in photon arrival become larger relative to the mean signal. This Poisson-based variation shows up as a grainy, speckled appearance in the image, known as quantum noise. The image becomes noisier because the signal-to-noise ratio drops with fewer photons, not because the image gains sharpness or contrast. Fogging would come from scatter and veil the image, and sharpness relates to geometric factors like focal spot size, not exposure level; contrast is mainly affected by kVp and subject contrast. So the hallmark degradation from low mAs is quantum noise.