Patients are five times as likely to receive a CT scan in the U.S. as in the U.K., said Dr. Craft.

WSJ: Childhood CT Scans Pose Cancer Risk

In the U.S., use of CT scans quadrupled to 85.3 million in 2011 since the early 1990s.

WSJ: Childhood CT Scans Pose Cancer Risk

Efforts are under way in the U.S. to curb overuse of CT scanning in children, including the Image Gently initiative, launched in August 2009 and spearheaded by a coalition of health-care organizations dedicated to changing medical practice.

WSJ: Childhood CT Scans Pose Cancer Risk

The number of scanners per capita in the U.S. is now 7x (for CT) and 2.5x (for MRI) the average of France and Germany, and many of these scanners are poorly utilized but still profitable for their owners at prevailing price levels.

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It examined the U.K.'s National Health Service records of patients who had received a CT before age 22 and looked at their medical history for an average of 10 years afterward.

WSJ: Childhood CT Scans Pose Cancer Risk

And rental prices in many major markets across the U.S. have been on the rise as less people own homes, making places like New Haven, CT, a city centered around college students and young adults, some of the Worst Cities for Renters.

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