Which statement best describes the relationship between OID and spatial resolution?

Which statement best describes the relationship between OID and spatial resolution?

• A. Small OID yields higher spatial resolution; large OID yields lower spatial resolution
• B. Small OID yields lower spatial resolution; large OID yields higher spatial resolution
• C. OID does not affect spatial resolution
• D. Spatial resolution is primarily a function of SID

Answer: (D)

Spatial resolution is governed by the imaging geometry. When you increase the source-to-image distance, the X-ray beams hitting the detector are more parallel, the magnification drops, and the geometric blur at edges—the penumbra—shrinks. That reduction in blur makes edges appear crisper, so the image resolution improves. Object-to-image distance can increase magnification and blur, but its effect is secondary to the overall projection geometry set by SID. In practice, changing SID has the larger impact on sharpness, so saying that spatial resolution is primarily a function of SID best describes the relationship.

Spatial resolution is governed by the imaging geometry. When you increase the source-to-image distance, the X-ray beams hitting the detector are more parallel, the magnification drops, and the geometric blur at edges—the penumbra—shrinks. That reduction in blur makes edges appear crisper, so the image resolution improves. Object-to-image distance can increase magnification and blur, but its effect is secondary to the overall projection geometry set by SID. In practice, changing SID has the larger impact on sharpness, so saying that spatial resolution is primarily a function of SID best describes the relationship.