Children undergoing complex imaging tests like computed tomography (CT) scans for heart problems may have higher cancer risks over their lifetime, according to a study released Monday by the American Heart Association journal Circulation.

These tests, also including cardiac catheterization procedures using video X-rays called fluoroscopies, may expose children to higher doses of radiation than standard X-rays do, researchers at Duke University Medical Center said.

Radiation from standard X-rays, however, is relatively low and doesn't significantly raise lifetime cancer risks for most young children, they said.

"There are definitely times when radiation is necessary," Kevin Hill, lead author and cardiologist and assistant professor of pediatrics in the cardiology division at Duke, said in a statement.

"But it's important for parents to ask and compare in case you can avert potentially high exposure procedures. Often, there are alternative or modified procedures with less radiation, or imaging may not actually be necessary," he said.

The researchers followed 337 children under age six who had surgery for heart disease, since children with heart disease are exposed to more imaging tests than most young patients. These children received almost 14,000 imaging procedures, including X- rays, cardiac catheterizations and CT scans.

The researchers reviewed medical records to find the most common imaging procedures, calculated how much radiation organs absorb during each procedure, then analyzed lifetime cancer risks based on the amounts of each procedure's exposure.