Vortex ultrasound breaks down blood clots

The new approach by US universities, including a team at North Carolina State University (NC State), was used to eliminate clots formed in an in vitro model of cerebral venous sinus thrombosis (CVST).

“Our previous work looked at various techniques that use ultrasound to eliminate blood clots using what are essentially forward-facing waves,” said Xiaoning Jiang, the Dean F. Duncan Professor of Mechanical and Aerospace Engineering at NC State and co-corresponding author of a paper on the work. “Our new work uses vortex ultrasound, where the ultrasound waves have a helical wavefront. 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 fact that our new technique works quickly is important, because CVST clots increase pressure on blood vessels in the brain,” said Chengzhi Shi, co-corresponding author of the work and an assistant professor of mechanical engineering at Georgia Tech. “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.”

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 United States in 2018 and 2019, and the incidence rate is said to be increasing.

“Another reason our work here is important is that current treatments for CVST fail in 20-40 per cent of cases,” Jiang said in a statement.

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

For proof-of-concept in vitro testing, the researchers used cow blood in a 3D-printed model of the cerebral venous sinus.

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

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

The researchers found also that vortex ultrasound did not cause substantial damage to red blood cells.

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

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

The paper, “A Model of High-Speed Endovascular Sonothrombolysis with Vortex Ultrasound-Induced Shear Stress to Treat Cerebral Venous Sinus Thrombosis,” is published in Research.