CT scans are as effective as traditional "functional stress tests" for patients displaying symptoms of heart disease, although not without their own risks, a new study indicates.

The results came as something of a surprise, researchers said, because expectations were that CT scans - an advanced form of X-ray imaging that can yield 3D images of heart arteries - would be better than a simple treadmill test or other older functional diagnostic tests.

The 3D images allow doctors to gauge the amount of narrowing in the heart's arteries, whereas a functional tests uses electrical signals, ultrasound or other imaging techniques to assess the heart's response to stress.

Both CT scans and traditional functional tests have long been employed, but the new study, using federal government funding to the tune of $40 million, is the first to compare them head-to-head based on patient outcomes, a team headed by cardiac disease expert Dr. Pamela Douglas of Duke University says.

"Until this study, we have essentially been guessing on decisions about which initial test to use for this huge population of patients who need evaluation for cardiovascular symptoms," she says.

In the study, half of patients had received CT scans, while the other half was given whichever other test their doctor selected to evaluate how healthy their hearts were, in terms of whether it was getting sufficient blood from heart arteries.

"Our study shows that the prognostic outcomes are excellent and are similar regardless of what type of test you use, but there are some indications that [CT] might be the safer test," she explained.

That's because a CT scan involves much less radiation than the most popular functional test, known as a nuclear stress test, which involved injecting radioactive dye to make blood vessels show up on X-ray images.

CT scans were also found to be more accurate in identifying patients who require follow-up testing and/or artery-opening medical procedures, the researchers say.

CT scans "more accurately detects blockages and also more accurately excludes them," says study leader Douglas.

However, while CT scans involve less radiation, the study "does expose that there are risks to many of these tests," says Dr. Jeffrey Kuvin, chief of cardiology at Tufts Medical Center in Boston.

The study found that, while radiation can increase the risk of developing cancer, most doctors are still choosing heart tests involving some form and level of radiation.

The study results, presented at an American College of Cardiology conference in San Diego, have also been published in the New England Journal of Medicine.

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