Reviewed by Lexie CornerOct 1 2024
Researchers from the California Institute of Technology have developed a laser-based device that can be worn on the head to non-invasively monitor changes in brain blood flow and volume. This device offers a direct method of assessing stroke risk based on physiological markers. The study was published in Biomedical Optics Express.
Researcher Simon Mahler is wearing the laser device, which has six channels for monitoring cerebral blood flow and blood volume. Image Credit: Simon Mahler and Yu Xi Huang, California Institute of Technology
Strokes occur when blood flow to the brain is reduced or blocked, causing severe damage to brain cells. They are the second leading cause of death and a major contributor to long-term disability, affecting around 15 million people worldwide each year.
The lack of a cost-effective and scalable stroke risk assessment system complicates long-term stroke prevention because a physician cannot tell whether a patient’s risk is stable or worsening. 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.
Simon Mahler, Postdoctoral Scholar and Research Team Member, California Institute of Technology
The researchers describe their method, which uses speckle contrast optical spectroscopy (SCOS) to track changes in blood flow and volume during a breath-holding exercise. In a group of fifty volunteers, the portable system successfully identified stroke patients with varying levels of risk. This research is part of a broader collaboration led by Charles Liu and Yang at 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 explored various techniques to assess changes in cerebral blood flow and stroke risk. Measuring blood flow during stress events in the brain, such as breath-holding, is one way to evaluate stroke risk.
Imaging methods like PET, SPECT, and CT can detect these changes but are costly and impractical for routine clinical use or large-scale screening. To address this, the researchers used SCOS, a simpler and more accessible method to measure brain blood flow and volume changes.
They developed a handheld spectroscopic system using a CMOS-based camera and a laser diode that can be worn on the head, eliminating the need for external optical components. SCOS works by illuminating the brain with infrared light and analyzing the resulting scattered light patterns. The infrared light penetrates the skull and brain, producing a speckle pattern that changes with tissue oxygenation and blood flow.
By using a coherent laser, the system measures the rate of change in the laser speckle field, which increases with higher blood flow, providing a direct measure of brain blood flow.
Simplified Blood Flow Assessment
As people age, their blood vessels get stiffer, making them more prone to stroke. 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.
Charles Liu, University of Southern California
The researchers divided 50 participants into low- and high-risk stroke groups using the Cleveland Stroke Risk Calculator. They then applied the SCOS approach to observe variations in blood flow and volume, finding significant differences between the two groups. These variations suggest that these physiological indicators could be used to assess 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 exploring the integration of machine learning to improve data analysis and validate the method's effectiveness.
Journal Reference:
Huang, X. Y., et al.(2024) Correlating Stroke Risk with Non-Invasive Cerebrovascular Perfusion Dynamics using a Portable Speckle Contrast Optical Spectroscopy Laser Device. Biomedical Optics Express. doi.org/10.1364/boe.534796.