Mapping the brain’s hidden highways through sound waves and tiny bubbles
Researchers are developing a non-invasive, high-resolution imaging tool to detect neurovascular conditions by “listening to” how blood flows through the brain’s microvascular system.

In Canada, stroke remains a major health concern, affecting approximately 100,000 adults each year. Early changes linked to stroke and other neurovascular conditions often begin in the brain’s smallest blood vessels, known as capillaries.

“Capillaries are some of the most important microvascular systems in the brain,” explains Dr. Stephen Lee, who is completing his Postdoctoral Fellowship at Polytechnique Montréal. They deliver oxygen, bring nutrients, and clear away waste, keeping the brain healthy. These vessels also interface with brain cells and the immune system.

When capillaries stop working properly, people may experience memory loss, mood changes, or movement problems. Because of their microscopic size and location deep within the brain, these early warning signs are difficult to detect, with non-invasive imaging tools. As a result, critical information is often missed, limiting clinicians’ ability to diagnose and intervene sooner.

At Polytechnique Montréal, the Provost Ultrasound Lab is working to address this knowledge gap. Motivated by the need for earlier, more precise detection of neurovascular and neurodegenerative conditions, Dr. Jean Provost’s team is developing innovative ways to visualize the brain’s microvascular system.

As part of the team, Dr. Lee has always been passionate about music and fascinated by how sound can reveal what the eye cannot see. That curiosity, and the lack of non-invasive tools that capture capillaries, inspired a creative solution.

With support from NSERC and a CIHR postdoctoral award—now part of CIHR Health Training Research Awards—Dr. Lee helped develop a new imaging system called Single Capillary Reporters. It combines ultrasound technology with tiny bubbles of gas. Injected into the bloodstream, these microbubbles easily respond to sound waves and can be tracked as they move through the brain.

By following their path, the novel ultrasound technique builds a detailed, real-time map of individual capillaries, without the need for invasive procedures.

“In animal models, we could see how each bubble moved through the entire vascular network,” Dr. Lee says. “This means we gained insight into the behaviour of single capillaries hidden deep in the brain.” Single Capillary Reporters can also measure the direction and speed of blood flow, offering clues about potential problems in specific areas.

While similar ultrasound-based systems can generate static images of microscopic vessels, Dr. Lee’s method provides a dynamic picture of how blood moves through them over time—much like how Google Maps tracks traffic throughout the city in real-time.

Although still under development, Single Capillary Reporters show strong potential. If implemented in the future, the system could help health care providers identify people at risk of conditions like stroke earlier, improve diagnostic accuracy, and monitor how well treatments are working.

The Provost Ultrasound Lab team is now studying how microvascular systems respond to different neurological conditions, with the goal of identifying individualized microvascular patterns and supporting more personalized care.

At a glance

Issue

Stroke affects an estimated 100,000 Canadians each year. The brain’s smallest vessels may reveal early signs of neurovascular and neurodegenerative conditions, but current non-invasively imaging tests cannot clearly capture activity at this microscopic level. This means early warning signs are often missed.

Research

Dr. Stephen Lee is developing an ultrasound-based system to map the pathway of the brain's smallest blood vessels with the use of microbubbles of gas. A diagnostic system capable of showing this level of detail without the need for invasive procedures could transform how neurovascular conditions like stroke are detected and treated.