Blurring at the edges of an object on a radiograph is referred to as what?

Blurring at the edges of an object on a radiograph is referred to as what?

• A. Magnification
• B. Penumbra
• C. Quantum mottle
• D. Ghosting

Answer: (B)

Penumbra is the gradual transition at the edges of an object on a radiograph. It occurs because the X-ray beam is divergent and the focal spot has finite size, so rays from different parts of the focal spot illuminate neighboring margins differently. This creates a partial shadow around edges instead of a perfectly sharp boundary. The amount of penumbra depends on the focal spot size and the geometry: a larger focal spot or greater object-to-image distance increases the edge blur, while a longer source-to-image distance reduces it. Magnification changes the overall size of the image, not the edge sharpness, and other terms describe graininess or nonuniformities rather than edge blur.

Penumbra is the gradual transition at the edges of an object on a radiograph. It occurs because the X-ray beam is divergent and the focal spot has finite size, so rays from different parts of the focal spot illuminate neighboring margins differently. This creates a partial shadow around edges instead of a perfectly sharp boundary. The amount of penumbra depends on the focal spot size and the geometry: a larger focal spot or greater object-to-image distance increases the edge blur, while a longer source-to-image distance reduces it. Magnification changes the overall size of the image, not the edge sharpness, and other terms describe graininess or nonuniformities rather than edge blur.