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‘Ultrasound tornado’ breaks down blood clots in brain model

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An illustration of how the vortex ultrasound can break down blood clots (Credit: Xiaoning Jiang and Chengzhi Shi)
An illustration of how the vortex ultrasound can break down blood clots (Credit: Xiaoning Jiang and Chengzhi Shi)

A new technique that creates ‘ultrasound tornadoes’ could be used to break down blood clots in the brain, its creators have said.

The approach eliminated clots in a model of part of the brain quicker than existing techniques, said the researchers who developed the technique at North Carolina State University.

“Our previous work looked at various techniques that use ultrasound to eliminate blood clots using what are essentially forward-facing waves,” said mechanical engineer Professor Xiaoning Jiang, co-corresponding author of a paper on the work.

“Our new work uses vortex ultrasound, where the ultrasound waves have a helical wavefront. In other words, the ultrasound is swirling as it moves forward. Based on our in vitro testing, this approach eliminates blood clots more quickly than existing techniques, largely because of the shear stress induced by the vortex wave.”

The new tool consists of a single transducer that is specifically designed to produce the swirling vortex effect. The transducer is small enough to be incorporated into a catheter, which would be fed through the circulatory system to the site of the blood clot.

The team used cow blood in a 3D-printed model of the cerebral venous sinus for proof-of-concept testing.

“Based on available data, pharmaceutical interventions to dissolve CVST blood clots take at least 15 hours, and average around 29 hours,” said co-corresponding author Chengzhi Shi. “During in vitro testing, we were able to dissolve an acute blood clot in well under half an hour.”

CVST occurs when a blood clot forms in the veins responsible for draining blood from the brain. Incidence rates of CVST were between two and three per 100,000 in the US in 2018 and 2019, and appear to be increasing. Current treatments for CVST fail in 20-40% of cases, Jiang added.

“The fact that our new technique works quickly is important, because CVST clots increase pressure on blood vessels in the brain,” said Shi. “This increases the risk of a haemorrhage in the brain, which can be catastrophic for patients.

“Existing techniques rely in large part on interventions that dissolve the blood clot, but this is a time-consuming process. Our approach has the potential to address these clots more quickly, reducing risk for patients.”

During any catheterisation or surgical intervention there is a potential risk of harm, the researchers said, such as damaging the blood vessel itself. To address this issue, they performed experiments applying vortex ultrasound to animal blood vein samples. Those tests found no damage to the blood vessel walls.

The team also conducted tests to determine whether the vortex ultrasound caused significant damage to red blood cells, and found that there was not substantial damage.

“The next step is for us to perform tests using an animal model to better establish the viability of this technique for CVST treatment,” said Jiang. “If those tests are successful, we hope to pursue clinical trials.”

Shi added: “If the vortex ultrasound ever becomes a clinical application, it would likely be comparable in cost to other interventions used to treat CVST.”

The work was published in open-access journal Research.

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