Hi, Thanks for writing in. A single S ray is not a concern in an infant when done for medical investigative purpose. This can be ignored. CT scan is to be avoided in those younger than 15 years of age because of the radiation dose. In a CT scan the dose is equivalent to 200 X rays. This is a high dose and should be avoided unless there is an obvious benefit arising by doing such an investigation. Research shows that those kids having exposed to two or more CT scans below 15 years of age have a two fold risk of developing leukemia later in life. However since you child got only X ray done hence there is no concern for radiation exposure. Please do not worry.