A decrease in SID primarily increases which aspect of the image?

A decrease in SID primarily increases which aspect of the image?

• A. Increased penumbra
• B. Increased spatial resolution
• C. Decreased noise
• D. No change

Answer: (A)

Decreasing the distance from the X-ray source to the image receptor makes the X-ray beams diverge more as they travel, which increases geometric unsharpness at edges. This added blur around high-contrast structures is the penumbra, and it grows when SID is reduced. As a result sharpness and the ability to discern fine details worsen, not improve, so increasing spatial resolution isn’t correct. Noise isn’t primarily controlled by SID, and some change in edge sharpness occurs, so “no change” isn’t accurate either. The key effect of a shorter SID is a larger penumbra.

Decreasing the distance from the X-ray source to the image receptor makes the X-ray beams diverge more as they travel, which increases geometric unsharpness at edges. This added blur around high-contrast structures is the penumbra, and it grows when SID is reduced. As a result sharpness and the ability to discern fine details worsen, not improve, so increasing spatial resolution isn’t correct. Noise isn’t primarily controlled by SID, and some change in edge sharpness occurs, so “no change” isn’t accurate either. The key effect of a shorter SID is a larger penumbra.