Which of the following factors does NOT contribute to degraded spatial resolution?

• A. Long SID
• B. Long OID
• C. Large focal spot
• D. Magnification

Answer: (A)

Spatial resolution in radiography is shaped by geometric factors that determine how sharp or blurred an image appears. The blur, or geometric unsharpness, is roughly proportional to the focal spot size multiplied by the object-to-image distance and divided by the source-to-image distance. That means:

• A larger focal spot increases blur, degrading resolution.

• A greater object-to-image distance increases blur, degrading resolution.

• A shorter source-to-image distance increases blur, degrading resolution.

Conversely, increasing the source-to-image distance (long SID) reduces geometric unsharpness, which improves spatial resolution. Magnification happens when there is any object-to-image distance, and it is inherently tied to the same geometric relationships; greater magnification typically accompanies more blur if the geometry isn’t adjusted, but the direct factor that does not contribute to degradation is simply a long SID, since it reduces blur and sharpness improves.