Researchers have created a device that uses lasers to measure blood flow in a noninvasive way, helping to identify stroke risk based on a person’s current health status.
When doctors want to evaluate a patient’s risk for heart disease, they can order a cardiac stress test. Unfortunately, there’s no similar scalable or affordable way to assess brain health and stroke risk. At present, the most effective approach is a questionnaire that gathers information about risk factors from the patients themselves.
Recently, a group of engineers and scientists from Caltech and the Keck School of Medicine at USC developed a headset device that can noninvasively evaluate stroke risk by observing blood flow and volume changes while a participant holds their breath. This innovative device employs a laser system and has shown encouraging results in distinguishing between low and high stroke risk individuals.
Stroke is a significant health issue, affecting nearly 800,000 Americans annually, making it the primary cause of serious, long-term disabilities in the country. Strokes occur when an artery in the brain is either blocked or ruptured, leading to diminished blood flow. This oxygen deprivation quickly results in the death of brain cells, at a rate of about 2 million cells every minute during a stroke.
“For the first time with this device, we can assess the likelihood of someone experiencing a stroke in the future using physiological measurements,” remarks Simon Mahler, a co-lead author of the study featured in Biomedical Optics Express. He is also a postdoctoral scholar in Changhuei Yang’s lab at Caltech, where Yang holds the Thomas G. Myers professorship in Electrical Engineering, Bioengineering, and Medical Engineering and serves as a Heritage Medical Research Institute Investigator. “We believe this could fundamentally change how stroke risk is evaluated and ultimately assist doctors in determining whether a patient’s risk is stable or deteriorating.”
“Our optical technology designed for measuring blood flow noninvasively is projected to be beneficial across various brain disease scenarios,” adds Yang, who also oversees electrical engineering at Caltech. He pointed out that this initiative is part of an extensive collaborative effort with Dr. Charles Liu, who is a professor and expert in several areas at the Keck School of Medicine of USC.
Speckle Contrast Optical Spectroscopy for Stroke-Risk Assessment
Generally, as people age, their blood vessels become stiffer, which means they struggle to expand and allow blood circulation. This stiffness heightens susceptibility to strokes.
The Caltech team constructed a compact device that directs infrared laser light through the skull, targeting a specific brain area, and employs a special camera to capture light reflected back after interacting with blood. This method, called speckle contrast optical spectroscopy (SCOS), measures changes in light intensity from the entry point in the skull to the collection point of the reflected light, allowing researchers to determine the blood volume within the brain’s vessels. Furthermore, variations in light scattering create a speckle pattern in the camera’s view, which fluctuates in response to the blood flow rate in the vessels; faster blood flow leads to more rapid changes in the speckle field.
By analyzing these measurements, the researchers can calculate a flow-to-volume ratio, providing insights into an individual’s stroke risk.
In a study involving 50 participants, the team used the Cleveland Stroke Risk Calculator, the standard questionnaire for stroke risk, to categorize the participants into low and high-risk groups. They examined blood flow in each individual for three minutes, measuring both blood flow rate and the volume reaching the brain. After the first minute, participants were prompted to hold their breath.
Restricting breath creates stress as the brain realizes it’s receiving excess carbon dioxide and insufficient oxygen, pushing it into what Mahler describes as “panic mode,” increasing blood flow to itself. This reaction enhances oxygen supply to the brain. Although both low and high-risk individuals experience this response, noticeable differences in blood movement through the vessels were observed between the two groups.
The SCOS technique enabled researchers to assess how much blood vessels dilate while participants hold their breath and how blood flow velocity increases in reaction. “These measurements indicate vessel stiffness,” notes Yang. “For the first time, our technology allows noninvasive assessments of such characteristics.”
The Findings
“Our results reveal significant differences in blood flow and volume reactions between the two groups,” states Yu Xi Huang, another co-lead author and a graduate student in Yang’s lab.
In the low-stroke-risk category, researchers noticed a smaller increase in blood flow during breath-holding when compared to those in the high-stroke-risk group, but a greater increase in blood volume, suggesting improved blood flow through the widened vessels.
“We can observe that the higher-risk group exhibits a greater flow-to-volume ratio, characterized by swift flow yet lower blood volume during breath retention,” Mahler explains. This phenomenon, driven by blood vessel rigidity, poses a greater risk for rupture. “A person displaying an extremely high flow-to-volume ratio may indicate a likelihood of stroke in the near future.”
A Promising Future
The research team is performing further studies using the current prototype of the imaging device on patients at a hospital in Visalia, California, gathering more data from a broader and diverse population. They also plan to integrate machine learning into the device’s data collection and initiate a clinical trial that will involve tracking patients for over two years to improve the technology. Their aspiration is for the device to eventually be used widely for screening stroke risk and even for identifying specific locations in the brain where a stroke may have occurred.
Other contributors to the paper titled “Correlating stroke risk with non-invasive cerebrovascular perfusion dynamics using a portable speckle contrast optical spectroscopy laser device” include Julian Michael Tyszka, an associate director at Caltech Brain Imaging Center; and Dr. Aidin Abedi, Yu Tung Lo, Patrick D. Lyden, and Dr. Jonathan Russin from the Keck School of Medicine at USC. This effort received funding from the National Institutes of Health and the USC Neurorestoration Center.
