Increasing source-to-image distance (SID) changes radiographic density and detail in which way?

Increasing source-to-image distance (SID) changes radiographic density and detail in which way?

• A. Decrease density and increase detail
• B. Decrease density and decrease detail
• C. No change in density or detail
• D. Increase density and decrease detail

Answer: (B)

Increasing SID means the x-ray beam spreads out more before reaching the image receptor. Because of the inverse square law, fewer photons reach the receptor, so the image becomes lighter (density decreases) if mAs isn’t adjusted. At the same time, a larger SID reduces magnification and geometric unsharpness. The finite focal spot size causes less blur on the image, so spatial resolution improves and detail becomes sharper. If you adjust mAs to keep density constant when SID is increased, the density stays about the same, but the detail still improves due to reduced geometric blur. Overall, the typical result is decreased density with increased detail.

Increasing SID means the x-ray beam spreads out more before reaching the image receptor. Because of the inverse square law, fewer photons reach the receptor, so the image becomes lighter (density decreases) if mAs isn’t adjusted.

At the same time, a larger SID reduces magnification and geometric unsharpness. The finite focal spot size causes less blur on the image, so spatial resolution improves and detail becomes sharper.

If you adjust mAs to keep density constant when SID is increased, the density stays about the same, but the detail still improves due to reduced geometric blur. Overall, the typical result is decreased density with increased detail.