It's a wonderful, Star-Trek kind of fantasy: have a machine scan your body and turn up any abnormalities in minutes, with no pain, no inconvenience and little fuss. Some patients actually do it: with whole-body CT scans, or more targeted CT scans aimed at the colon (often called virtual colonoscopy -- President Obama had one) or the heart. The problem is there's no good evidence yet that these scans are worth the expense or the huge dose of X-ray radiation that a patient receives: typically the equivalent of 400 chest X-rays with a single CT scan.
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