The new study also suggests that the new scanners, four times quicker than the more widely used 16-CT, may be a good alternative to cardiac stress testing, which evaluates heart function by measuring the effects of hard exercising. Exercise stress testing enerally cannot safely be performed on the weak and elderly.

"Use of 64-CT scans will dramatically improve our ability to detect and treat people with suspected coronary disease and chest pain much earlier in their disease," says cardiologist Jo?o Lima, M.D., senior investigator to the team whose findings will be presented Nov. 5 at the American Heart Association's (AHA) annual Scientific Sessions in Orlando, Fla. "Cardiac catheterization is still the gold standard for evaluating clogged arteries, but our results show that this test could easily be the best backup or alternative."


In cardiac catheterization, a thin tube is threaded into a blood vessel in the groin area to the heart's arteries, where a dye is released to produce a clear X-ray image of the beating heart and its arterial blood supply. In CT imaging, computer-driven machinery passes X-rays through the body, producing digitized signals or "slices" that are detected and reconstructed for a precise picture.

Blocked arteries are the most frequent trigger of heart attack, says Lima, an associate professor of medicine and radiology at the Johns Hopkins University School of Medicine and its Heart Institute. The latest estimates from the AHA show that one in five deaths in the United States each year is due to coronary heart disease (653,000 deaths in 2004), including 157,000 who die from heart attack.

Miller, an assistant professor at Johns Hopkins, says the advanced scanners are so good that physicians can for the first time measure blockages in blood vessels as small as 1.5 millimeters in diameter. Older 16-CT scanners, she says, are best suited for looking inside bigger arteries, those ranging in diameter from 2 millimeters to 4.5 millimeters, and to calculate the amount of calcium buildup in the arteries, also a predictor of the degree of blockage, "but now we have a more-advanced test that actually measures the amount and volume of blockage present."

She says older scanners were not as powerful, either, unable to image as much as 25 percent of the smaller blood vessels that branch out from the heart's main arteries. However, the 64-CT scanner picks up as much as 98 percent of the heart's arterial network (and lacks good images for only 2 percent.)

Miller points out that early detection of blockages is critical to pre-empting a heart attack, allowing time for drug therapy, angioplasty or heart bypass surgery to be used to keep arteries open. In coronary artery disease, hardened bits of fat and dead tissue, called plaque, build up along the inside wall of the blood vessels, impeding the body's natural blood flow and leaving the narrowed opening more vulnerable to formation of blood clots.

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