It's no secret that some medical exams expose patients to harmful radiation. But how much is too much?
Recent studies have raised the alarm about one increasingly common source: the computed tomography (CT) scan, which doctors use to diagnose and treat everything from concussions to infections to cancer. Dr. Rebecca Smith-Bindman of the University of California, San Francisco, and her team report in one study that usage has tripled since 1996--a concern, since CT devices tend to emit much more radiation than conventional X-rays in order to take detailed pictures of internal organs. For children, the risk may be especially high....