ORLANDO, Fla. — A type of "super X-ray" showed promise in its first big test as a potentially cheaper, faster and painless way to find out whether certain people with signs of heart disease actually have it and need treatment.

The scans might eliminate the need for some of the 1.3 million cardiac catheterizations done each year in the United States to check for clogged arteries, said Dr. Julie Miller of Johns Hopkins University.

But the newer scans are controversial. Medicare and private insurers are debating whether to pay for them, and many heart specialists oppose them, partly because they supply a big dose of radiation.

That raises the risk of cancer and might spur thousands of additional cases if the scans were widely used in the population, said Dr. Michael Lauer of the National Heart, Lung and Blood Institute.

Speaking at an American Heart Association conference where study results of the scan were presented Monday, he called on doctors not to use the scans until research proves they save lives.

"I think he went a little overboard" and was reacting to worries the scans would be used to screen people with no symptoms, rather than the more limited use tested in the study, said Miller, who led the research.

This new CT scan technology came on the market two years ago and is already used by many hospitals. Because it uses 64 detectors to produce and combine images, the scans are called "64-slice CT." The images are so detailed that one doctor described them as an almost surgical view.

In the new study, the scans were tested against the current gold standard method of checking a patient for heart disease: angiograms done in a cardiac catheterization lab. A tube is placed in a blood vessel in the groin and maneuvered near the heart, and a special dye is infused that makes the arteries show up on X-rays.

These can reveal who has blockages and needs treatment with bypass surgery or an artery-opening procedure called balloon angioplasty.

The new scans deliver 10 times more radiation to the patient than a standard angiogram. Though the technology has been in use, its accuracy hasn't been proved.

Miller's international study was the first direct comparison. It was funded by scanner maker Toshiba Medical Systems, and Miller has had research grants from the company.

Researchers started with 405 people suspected of having heart disease and eliminated about one-fourth because they had high amounts of calcium in their artery walls. This is common as people age and the arteries harden, and doctors worried that such findings could look like blockages and bias results.

The remaining 291 people were given the new CT scans, then standard angiograms.

Nine of 10 patients with blockages were identified by the scans, as were 83 percent of those without blockages. The scans ruled out heart disease in half of the patients — people who could have been spared the pain, expense and risk of catheterization, Miller said.

The ability of the painless scans to rule out problems is "exciting," but questions remain about how they would do on a fuller range of patients, said Dr. Timothy Gardner, a cardiologist and heart association spokesman.

The association recently sent Medicare officials a letter opposing the scans for screening people with no heart disease symptoms, but saying they could be considered for those with symptoms or to check for heart defects, said Dr. Raymond Gibbons of the Mayo Clinic, a former heart association president.

The new scans cost under $1,000; angiograms from catheterization cost $2,500 or more.