Quantum mottle is observed as what in DR images?

• A. Graininess Due to Insufficient Photon Flux
• B. Fixed-Pattern Noise From Detector Electronics
• C. Motion Artifact
• D. Contrast Enhancement

Answer: (A)

Quantum mottle comes from the randomness of photon arrival. When exposure is low, only a small number of x-ray photons reach the detector, and photon detection follows a Poisson distribution. The noise level is proportional to the square root of the number of detected photons, so the signal-to-noise ratio is 1 over the square root of N. With few photons, this relative noise becomes noticeable, producing the grainy, mottled look in the image. This is why increasing exposure (photon flux) reduces the mottle and improves image graininess, within patient-dose limits. Fixed-pattern noise is due to detector electronics and appears as consistent patterns regardless of exposure, motion artifact shows up as blur from movement, and contrast enhancement refers to processing changes in tonal separation, not random photon noise.