An under-exposed radiographic image may exhibit which artifact?

• A. Mottle
• B. Distortion
• C. Saturation
• D. Penumbra

Answer: (A)

Underexposure creates a photon-limited image, so the detector receives too few photons to produce a uniform signal. The resulting random fluctuations in pixel values, known as quantum mottle or photon noise, give the image a grainy, mottled appearance. This mottling reduces visibility of detail and overall image quality when there aren’t enough photons to form a smooth, continuous image.

Distortion, saturation, and penumbra arise from other factors: distortion comes from improper alignment or positioning, saturation from excessive exposure that clips density in bright areas, and penumbra from geometric factors like focal spot size and distances affecting edge sharpness.