Times Staff and Wire Reports

Americans may be receiving too much radiation from medical tests whose value has not been proven, researchers reported in the New England Journal of Medicine.

More than two-thirds of Americans underwent at least one such imaging procedure in the three years covered by the study, reported Dr. Reza Fazel and colleagues at Emory University School of Medicine in Atlanta.

The two biggest contributors to the radiation exposure are CT scans, which use a series of X-rays to produce a three-dimensional image of the body, and heart perfusion scanning to measure blood flow through the arteries leading to the heart. In that test, radioactive technetium-99m is injected into blood vessels and its progress through the heart is monitored with external radiation detectors.

Radiation is known to cause cancer, typically years after exposure. By some estimates, medical testing radiation is responsible for 2% of all cancer cases, but experts fear that it may be higher in the future as more patients are exposed to these new procedures.

They are also concerned because more tests are being performed on younger people, which allows more time for tumors to develop, and on women, who normally live longer than men.

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