Which condition improves recorded detail?

• A. Focal spot size decreases
• B. SID increases
• C. OID increases
• D. Pixel size increases

Answer: (B)

Recorded detail hinges on geometric unsharpness from the finite focal spot. The amount of blur on the image depends on the focal spot size, the object-to-image distances, and the source-to-image distance. Geometric unsharpness is proportional to the focal spot size and the magnification factor (OID divided by SID). When you increase the source-to-image distance, magnification decreases and the blur projected from the focal spot becomes smaller on the image receptor, so the detail appears sharper. That’s why increasing SID improves recorded detail.

Keep in mind that increasing OID would worsen detail by increasing magnification and blur, and larger pixel size in a digital detector reduces sampling resolution. A smaller focal spot would also improve detail, but increasing SID is the most direct way to enhance sharpness in this scenario.