Researchers have developed a laser-based device that can be placed on the head to non-invasively monitor changes in brain blood flow and volume. The new device could one day help save lives by offering a direct and simple way to assess stroke risk based on physiological markers rather than indirect markers like lifestyle factors.

Strokes occur when blood flow to the brain is blocked or reduced, causing debilitating brain cell damage. With about 15 million people worldwide affected by strokes each year, it is the second leading cause of death and a leading cause of long-term disability.

“The lack of a cost-effective and scalable stroke risk assessment system complicates long-term stroke prevention because a physician can’t tell whether a patient’s risk is stable or worsening,” said research team member Simon Mahler, a postdoctoral scholar in Changhuei Yang’s laboratory at the California Institute of Technology. “This new method could help catch early signs of increased stroke risk, which is key to lowering the chances of having a stroke and reducing stroke severity.”

In the Optica Publishing Group journal Biomedical Optics Express, the researchers describe their approach, which uses speckle contrast optical spectroscopy (SCOS) to track changes in blood flow and volume during a breath-holding exercise. They report that the portable system was able to differentiate between low and high stroke risk in a group of 50 volunteers. The work is part of a larger collaboration led by Yang and Charles Liu from the University of Southern California.

This approach could one day be incorporated into the regular testing performed during annual physical examinations, providing physicians with crucial information about the patient’s health. It could be particularly beneficial for communities with limited access to advanced medical facilities and has the potential to lead to personalized strategies for reducing stroke risk.”

Charles Liu, University of Southern California

Spectroscopy on the go

For the past 40 years, researchers have been experimenting with various methods to measure blood flow in the brain and changes associated with stroke risk. Measuring blood flow when the brain is stressed, such as during breath holding, can be used to assess the risk of stroke.

Although imaging techniques like PET, SPECT and CT can reveal changes in blood flow, they are expensive and aren’t easy to use in clinics or for widespread community screening. To solve this challenge, the researchers turned to SCOS as a more practical way to access changes in blood flow and volume in the brain. They built a simple, portable spectroscopy system that consists of a laser diode and a CMOS-based camera that can be placed on the head with no external optical elements.

SCOS works by shining an infrared laser or light onto the brain and analyzing the patterns of scattered light. The infrared light can penetrate the skull and brain, producing a back-scattered speckle pattern that varies with changes in blood flow and tissue oxygenation. Using a coherent laser makes it possible to determine brain blood flow rate by calculating how fast the captured laser speckle field fluctuates, which speeds up with faster blood flow.

Simplified blood flow assessment

“As people age their blood vessels get stiffer, making them more prone to stroke,” said Yang. “By asking a person to hold their breath, we can use SCOS to measure how much the blood vessels expand and how much faster blood is flowing within the vessels in response. These reactive measurements are indicative of vessel stiffness, and such measurement capabilities are unique to transcranial optical methods.”

The researchers tested the SCOS method with 50 people who were divided into low- and high-risk stroke groups based on a stroke risk assessment performed with the Cleveland Stroke Risk Calculator. The researchers found that blood flow and blood volume changes were significantly different between the two groups and, therefore, have the potential to serve as physiological markers for stroke risk.

“While the current study is very promising, we are planning additional studies to further understand the clinical implications of the laser SCOS recordings in larger patient groups over longer time periods,” said Liu. They are also working to incorporate machine learning to improve data analysis and further validate the method’s effectiveness.