Dr. Steven Birnbaum works a CT scanner with a patient in this photo taken June 3 at Southern New Hampshire Medical Center in Nashua, N.H. Americans get the highest amounts of medical radiation worldwide.

We fret about airport scanners, power lines, cell phones and even microwaves. It’s true that we get too much radiation. But it’s not from those sources — it’s from too many medical tests.

Americans get the most medical radiation in the world, even more than folks in other rich countries. The U.S. accounts for half of the most advanced procedures that use radiation, and the average American’s dose has grown sixfold over the last couple of decades.

Too much radiation raises the risk of cancer. That risk is growing because people in everyday situations are getting imaging tests far too often. Like the New Hampshire teen who was about to get a CT scan to check for kidney stones until a radiologist, Dr. Steven Birnbaum, discovered he’d already had 14 of these powerful X-rays for previous episodes. Adding up the total dose, “I was horrified” at the cancer risk it posed, Birnbaum said.

After his own daughter, Molly, was given too many scans following a car accident, Birnbaum took action: He asked the two hospitals where he works to watch for any patients who had had 10 or more CT scans, or patients under 40 who had had five — clearly dangerous amounts. They found 50 people over a three-year period, including a young woman with 31 abdominal scans.

Of the many ways Americans are overtested and overtreated, imaging is one of the most common and insidious. CT scans — “super X-rays” that give fast, extremely detailed images — have soared over the last decade, often replacing tests that don’t require radiation, such as ultrasound and MRI, or magnetic resonance imaging.

Radiation is a hidden danger — you don’t feel it, and any damage usually doesn’t show up for years. Taken individually, tests with radiation pose little risk. Over time, the dose accumulates.

Doctors don’t keep track of radiation given their patients — they order a test, not a dose. Except for mammograms, there are no federal rules on radiation dose. Children and young women, most vulnerable to radiation harm, may get too much at imaging centers that don’t adjust doses for each patient’s size.

That may soon change. In interviews with The Associated Press, U.S. Food and Drug Administration officials described steps in the works, including possibly requiring device makers to print the radiation dose on each X-ray or other image so patients and doctors can see how much was given.

The FDA also is pushing industry and doctors to set standard doses for common tests. “We are considering requirements and guidelines for record-keeping of dose and other technical parameters of the imaging exam,” said Sean Boyd, chief of the FDA’s diagnostic devices branch.

A near-term goal: developing a “radiation medical record” to track dose from cradle to grave. “One of the ways we could improve care is if we had a running sort of Geiger counter” that a doctor checked before ordering a test, said Dr. Prashant Kaul of Duke University.

How much radiation is risky? The best guess is based on the 1986 Chernobyl nuclear power plant accident and studies of Japanese atomic bomb survivors who had excess cancer risk after exposures of 50 to 150 millisieverts (a measure of dose) of radiation.

A chest or abdominal CT scan involves 10 to 20 millisieverts, versus 0.01 to 0.1 for an ordinary chest X-ray, less than 1 for a mammogram, and as little as 0.005 for a dental X-ray. Natural radiation from the sun and soil accounts for about 2 millisieverts a year.

A big study last year estimated that 4 million Americans get more than 20 millisieverts a year from medical imaging.