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New Device Can Pinpoint Blood Clots

Detects stroke-causing clots that enter brain vessels during heart surgery

FRIDAY, Aug. 2, 2002 (HealthDayNews) -- A new kind of ultrasound device can now detect tiny stroke-causing blood clots that can enter brain blood vessels during heart surgery.

The results of two preliminary studies on the device, which is available in Europe but not the United States, are reported in the August issue of Stroke: Journal of the American Heart Association.

The device, called a multifrequency transcranial Doppler (MTCD), enables doctors to tell the difference between the tiny blood clots and gas bubbles that may enter the bloodstream during heart surgery and other heart procedures. The findings could help prevent stroke-causing blood clots and memory loss.

"In the past, we could detect something entering the arteries of the brain, but we could not tell if it was a very small gas bubble or blood clot. It was like a policemen who could detect a speeding vehicle but didn't know whether it was a small car or a large truck," says study author Dr. David Russell, a professor of neurology at The National Hospital in Oslo, Norway.

"With multifrequency transcranial Doppler, we can detect these small clots automatically, when they come into the brain, and the surgeon can change the technique to make it safer for the patient," Russell says.

MTCD generates sound waves at two different frequencies and sends the sound waves through the skull to create images that show blood flow through brain blood vessels. Conventional transcranial Doppler generates sound waves on one frequency.

"The distinction is important because a solid clot reflects back more ultrasound signal at the higher frequency, but gaseous bubbles reflect back more signal at the lower frequency," Russell says.

The laboratory and clinical studies involved 15 people with mechanical heart valves and 45 people with narrowing of the carotid (neck) arteries.

MTCD classified 100 percent of solid and gaseous objects and ruled out 99.3 percent of artificially generated clots in the laboratory study. In the clinical study, MTCD identified 98.6 percent of the gas and solid objects and correctly ruled out 98.9 percent of artificially generated clots.

The device was also able to distinguish between solid and gaseous clots.

In laboratory tests using solid plastic balls and gas bubbles flowing through a silicon tube immersed in water, MTCD was 95.6 percent successful in classifying the plastic balls as solid and 94.3 percent successful identifying gas bubbles as gaseous.

MTCD was then used to monitor blood flow through the middle cerebral artery in study participants. It accurately categorized 98.6 percent of clot-related events as solid or gaseous in heart valve patients and 94 percent of events in people with narrowing of the neck artery.

More information

The American Heart Association has more on blood clots.

SOURCE: American Heart Association, news release, Aug. 1, 2002
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