Answer to Question #12836 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
My infant son had a neck computerized tomography (CT) scan. Pediatric protocols were used. When looking at his scan I realized that the pajamas he wore contained a metal button and the button appeared in the image. I am now worried if there could be adverse effects or additional radiation exposure to my son due to radiation scatter. Could radiation scatter from this metal button have led to additional dose exposure?
There will be no adverse effects because a metal button was in the x-ray field. The button would make negligible difference in your son's radiation exposure.
Let's look at the possible fates of an x ray in a CT scanner. It can interact with an atom in the patient such that all of its energy is absorbed and it ceases to exist. Second, It could interact with an atom in the patient such that some of the energy is absorbed but a new, lower energy x ray, traveling in a new direction is formed. This new, lower-energy x ray traveling in a new direction is scatter radiation. The third fate is that it can pass through the patient and be "seen" by the image receptor. Different types of tissues have different probabilities for interaction. This is how images are created using x rays.
These fates apply to the x rays passing through the button as well. Presuming that the button is primarily iron, the ratio of the probabilities for absorption to scatter is greater in the button than in your son's body. Many more x rays were scattered by your son's body than were scattered by the button.
Again, the button on his pajamas is of no consequence in terms of additional dose.
Kent Lambert, CHP, FHPS