WEDNESDAY, April 27 (HealthDay News) -- The latest version of computerized X-ray scanning can give doctors the long-sought ability to tell whether someone has potentially fatal blood clots in the lung, European researchers report.

Multiple-slice computerized tomography, which sends an X-ray beam spinning rapidly around the body, met the challenge in a study of 756 patients, according to a report in the April 28 issue of the New England Journal of Medicine.

"This paper is very important because it validates multi-slice CT scanning as diagnosing or excluding pulmonary embolism [clots in the lung]," said Dr. Samuel Z. Goldhaber, the author of an editorial accompanying the report, and director of the Venous Thromboembolism Research Group and Anticoagulation Service at Brigham and Women's Hospital in Boston.

Older CT scanners, which produce a single image, do not do the job, Goldhaber noted. The European researchers used some scanners that produced four slices, or images, and others that produced 16 slices. With those machines, Goldhaber said, "you get very outstanding resolution, down to 1 millimeter. The old machines only gave 5-millimeter resolution."

The difference in resolution can be a matter of life or death. Pulmonary embolism is diagnosed yearly in an estimated 300,000 Americans, but may occur silently in at least three times as many more, according to the American Heart Association. The blood clots most often break off from veins in the legs and travel through the heart to the lung, which is why doctors urge airline passengers to minimize any threat on long-haul flights by walking around.

Pulmonary embolisms can be tricky for patients and doctors because the symptoms are often not clear-cut, Goldhaber said. The most common ones are unexplained shortness of breath or chest pains, particularly during a deep breath.

When such symptoms occur in someone at high risk of lung clots, "you should put them right in the CT scanner," Goldhaber said. In the European study, 82 patients were clearly identified as being at high risk. CT scans found lung clots in 78 of them.

But the cases of the other 674 patients were not so clear-cut. All of them were given a standard blood test looking for D-dimers, the breakdown products of blood clots. Those tests were negative for 232 patients, which removed the suspicion of lung clots. All the rest had multi-slice CT scans.

Those scans found clots in 109 patients. The scans were negative for 318 patients, only three of whom later had blood clots -- an accuracy rate of better than 98 percent.

The European results are being published before the findings of a major study in the United States, including hundreds of patients at eight medical centers. That study has been completed, said trial leader Dr. Paul D. Stein, formerly a cardiologist at St. Joseph Mercy Oakland Hospital in Pontiac, Mich. Stein said he would not comment on the European trial until data from the American study are published.

The American trial results might not be identical to those reported in Europe because the study first used single-slice CT scans before switching to multi-slice scans, Goldhaber noted. Previous studies have shown that single-slice scans miss about a third of lung clots, particularly the smaller ones, he added.

People who are suspected of having lung clots can play a role in diagnosis, Goldhaber said. Hospitals have a variety of CT scanners, he added. "You should ask for the multi-slice scanner," he said.

More information

You can learn all about pulmonary embolisms from the National Library of Medicine.