They found that for the average child in the study, the cumulative effective dose of ionizing radiation was relatively low, less than the annual background exposure in the United States.

However, some children with complex heart disease were exposed to large cumulative doses that increase the estimated lifetime risk of cancer up to 6.5 percent above baseline.

In all, lifetime cancer risk increases ranged from 0.002 percent for chest X-rays to 0.4 percent for complex CT scans and cardiac catheterizations.

Although X-rays accounted for 92 percent of all imaging exams, more complex tests like CT scans accounted for 81 percent of overall radiation exposure, the researchers said.

Specially, girls have double the cancer risks of boys because they're more prone to breast and thyroid cancers.

"Simple awareness is one of the greatest means to reducing exposure," Hill said. "Healthcare providers should consider tweaking protocols to limit radiation doses and balance risks and benefits of every imaging study they do."