Which term describes the edge blur at the boundary of an object on a radiographic image?

Which term describes the edge blur at the boundary of an object on a radiographic image?

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

Answer: (A)

The edge blur seen at the boundary of an object on a radiographic image is called penumbra. It happens because the X-ray beam comes from a finite focal spot and rays diverge as they travel to the image receptor, so the shadow of the object's edge isn’t a sharp line but a transition from dark to light. The amount of this unsharpness depends on focal spot size, how far the object is from the image receptor (OID), and how far the source is from the image receptor (SID). A larger focal spot or greater OID increases penumbra, while a longer SID decreases it. Magnification describes how large the image appears due to geometry, not the edge sharpness; ghosting is a residual image artifact, and quantum mottle is image noise from too few photons.

The edge blur seen at the boundary of an object on a radiographic image is called penumbra. It happens because the X-ray beam comes from a finite focal spot and rays diverge as they travel to the image receptor, so the shadow of the object's edge isn’t a sharp line but a transition from dark to light. The amount of this unsharpness depends on focal spot size, how far the object is from the image receptor (OID), and how far the source is from the image receptor (SID). A larger focal spot or greater OID increases penumbra, while a longer SID decreases it. Magnification describes how large the image appears due to geometry, not the edge sharpness; ghosting is a residual image artifact, and quantum mottle is image noise from too few photons.