When SID is increased in film-screen radiography, what changes occur?

When SID is increased in film-screen radiography, what changes occur?

• A. Decrease radiographic density and increase recorded detail
• B. Increase radiographic density and decrease detail
• C. Increase recorded detail
• D. No change

Answer: (A)

Increasing the distance from the x-ray source to the image receptor lowers the beam intensity reaching the film because of the inverse square law, so radiographic density decreases if exposure settings aren’t adjusted. At the same time, a larger distance reduces geometric blur (penumbra) and magnification, which improves the sharpness of the image and increases recorded detail. In short, you get less density but crisper detail when you raise SID. If you need the same density, you’d compensate by increasing mAs as SID is increased.

Increasing the distance from the x-ray source to the image receptor lowers the beam intensity reaching the film because of the inverse square law, so radiographic density decreases if exposure settings aren’t adjusted. At the same time, a larger distance reduces geometric blur (penumbra) and magnification, which improves the sharpness of the image and increases recorded detail. In short, you get less density but crisper detail when you raise SID. If you need the same density, you’d compensate by increasing mAs as SID is increased.