What is the term for blurring at the edges of an object on a radiograph?

What is the term for blurring at the edges of an object on a radiograph?

• A. Gaussian blur
• B. Motion blur
• C. Penumbra
• D. Focal blur

Answer: (C)

Penumbra is the blurred region at the edge of a radiographic image. This happens because the X-ray beam comes from a finite-sized focal spot and spreads out as it travels, so at the edge some rays illuminate the boundary differently. The result is a gradual transition from light to dark rather than a sharp line—the edge blur known as penumbra. The fully shadowed part is the umbra, while penumbra grows with larger focal spot size and greater geometric unsharpness. To reduce penumbra, you can increase the source-to-object distance and/or use a smaller focal spot, or decrease the object-to-image distance. Gaussian blur and motion blur are terms from image processing or describe movement, not the radiographic edge effect described here, and focal blur isn’t a standard radiography term.

Penumbra is the blurred region at the edge of a radiographic image. This happens because the X-ray beam comes from a finite-sized focal spot and spreads out as it travels, so at the edge some rays illuminate the boundary differently. The result is a gradual transition from light to dark rather than a sharp line—the edge blur known as penumbra. The fully shadowed part is the umbra, while penumbra grows with larger focal spot size and greater geometric unsharpness. To reduce penumbra, you can increase the source-to-object distance and/or use a smaller focal spot, or decrease the object-to-image distance. Gaussian blur and motion blur are terms from image processing or describe movement, not the radiographic edge effect described here, and focal blur isn’t a standard radiography term.