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Computer model offers 3-D view of aortic weak spots

'Virtual aneurysms' may one day help in deciding on surgery

Thursday, July 09, 1998

By Byron Spice, Science Editor, Post-Gazette

A bulge in the body's main artery, the aorta, is a scary thing. If this weak area of the artery blows, a person stands a good chance of bleeding to death. But most of these weak spots, called aneurysms, prove harmless.

So deciding whether to perform surgery, particularly in an older patient, can be a tricky business. Researchers at the University of Pittsburgh think they can provide some guidance, however, by constructing "virtual aneurysms."

By combining CT scans with computer modeling techniques, the researchers can provide a three-dimensional image of an aortic aneurysm that otherwise would remain hidden within a person's abdomen. Surgeons could rotate the computer image, with areas of stress highlighted in color.

"We're not at the point where we can take it to the clinic," said David Vorp, director of Pitt's Vascular Biomechanics and Vascular Research Lab. But results thus far have been promising and should provide surgeons with a better rule of thumb for determining when surgery might be necessary.

Abdominal aortic aneurysms, Vorp said, kill about 15,000 Americans every year, making them the 13th-leading cause of death.

Most people associate aneurysms with the brain, where they also can cause life-threatening bleeding, he said, but aneurysms are more common in the abdomen. For reasons not fully understood, the portion of the aorta that runs through the abdomen seems particularly thin and vulnerable to damage, he explained.

Abdominal aneurysms sometimes cause abdominal or back pain. Some people who are thin may actually feel the aneurysm, which feels like a pulsating mass.

But others cause no symptoms. In those cases, the aneurysm might be discovered by accident while doctors are analyzing a patient's gall bladder or performing an ultrasound study for some other reason.

Aneurysms also tend to run in families, so doctors increasingly are screening the siblings and offspring of patients who have abdominal aneurysms.

Once doctors find an aneurysm, however, it's not always clear which ones merit surgery. Repair requires a large abdominal incision and recuperation from surgery can take weeks. Many patients with aneurysms are older and most could safely live the rest of their lives without need for repair.

When an aneurysm bursts, however, 80 percent to 85 percent of patients either die immediately from bleeding or die in the operating room.

Surgeons now use the size of the aneurysm to judge its danger -- those bigger than 2 inches in diameter cause the most concern. But Vorp said autopsies had shown that smaller aneurysms can burst and many large aneurysms may be safe.

So Vorp and M.L. Raghavan, a doctoral student, use information from CT scans to construct 3-D images of the aneurysm so they can analyze its shape. They combine this information with the patient's blood pressure to calculate the amount of stress and the areas of greatest stress on the aneurysm.

Asymmetrical aneurysms and those that have a twisted shape seem to be most vulnerable to bursting, Vorp said.

Thus far, they have been unable to include information on the thickness of the aneurysm walls -- important information for evaluating an aneurysm's tendency to burst. That will require improvements in CT scanning technology.

"We're hoping we can get this wall thickness problem worked out in the next couple of years," he said.

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