What is the recommended source-to-skin distance in mobile radiography?

• A. 6 inches
• B. 12 inches
• C. 24 inches
• D. 36 inches

Answer: (B)

In mobile radiography, the distance from the X-ray source to the patient’s skin is chosen to balance patient dose with image quality and practical positioning. The recommended source-to-skin distance is twelve inches. This distance helps keep skin exposure at a reasonable level by moderating the dose through the inverse-square relationship, while still allowing adequate image geometry and maneuverability of the portable unit and detectors.

If the distance were much shorter, like six inches, the skin dose would rise significantly due to the inverse-square law, increasing patient radiation exposure. If the distance were much longer, such as twenty-four or thirty-six inches, magnification and geometric unsharpness would degrade image quality, making the exam harder to interpret and sometimes requiring higher technique. Twelve inches provides a practical compromise between dose management and image quality on mobile systems.