What is the source-to-skin distance for mobile radiography?

What is the source-to-skin distance for mobile radiography?

• A. 12 inches
• B. 24 inches
• C. 6 inches
• D. 8 inches

Answer: (A)

The main idea is that in mobile radiography you must keep the X‑ray source a certain minimum distance from the patient’s skin to limit skin dose. This minimum is 12 inches (about 30 cm). The dose at the skin increases rapidly as you get closer to the source (inverse-square relationship), so staying at least 12 inches away helps keep skin exposure reasonable while still allowing practical positioning of the portable unit. Distances shorter than this would dramatically raise skin dose and aren’t acceptable, while a longer distance (like 24 inches) is fine but not the minimum requirement—the question asks for the minimum.

The main idea is that in mobile radiography you must keep the X‑ray source a certain minimum distance from the patient’s skin to limit skin dose. This minimum is 12 inches (about 30 cm). The dose at the skin increases rapidly as you get closer to the source (inverse-square relationship), so staying at least 12 inches away helps keep skin exposure reasonable while still allowing practical positioning of the portable unit. Distances shorter than this would dramatically raise skin dose and aren’t acceptable, while a longer distance (like 24 inches) is fine but not the minimum requirement—the question asks for the minimum.