Strokes are the leading cause of neurological disability, with nearly 90% resulting from reduced or blocked blood flow to part of the brain, causing brain cell death. Despite this, there is no widely accessible method to screen patients for physical signs that a stroke may be imminent. While physicians can order cardiac stress tests to assess cardiovascular disease risk, there is no comparable, scalable, and cost-effective test to evaluate stroke risk. Currently, the best tool for estimating stroke risk is a questionnaire that considers various contributing factors. Now, researchers have developed a potential new method to measure stroke risk that is both noninvasive and cost-effective, similar to a cardiac stress test. If further validated, this device could revolutionize stroke care, making early detection of increased risk a routine part of medical exams worldwide.

A team of engineers and scientists from Caltech (Pasadena, CA, USA) and the Keck School of Medicine of USC (Los Angeles, CA, USA) has created a headset-based device that noninvasively monitors changes in blood flow and volume while the patient holds their breath, providing a new way to assess stroke risk. The device uses a laser-based system and has shown potential for distinguishing between individuals at low and high risk of stroke. It works by shining infrared laser light through the skull into the brain, and a nearby special camera collects the light that scatters back after interacting with blood in the vessels.

This technique, known as speckle contrast optical spectroscopy (SCOS), measures the reduction in light intensity from the point where it enters the skull to where it is collected, determining blood volume in the brain’s vessels. The light scattering also creates speckles in the camera's field of view, which fluctuate based on the rate of blood flow. The faster the blood flow, the quicker the speckle field changes. By calculating the ratio of blood flow to volume, researchers can estimate a patient’s stroke risk. In a proof-of-concept study, 50 participants wore the device while undergoing a breath-holding "stress test" for the brain. The SCOS device successfully differentiated between individuals with high and low stroke risk based on changes in blood flow and volume during the test. In the low-risk group, there was a smaller increase in blood flow but a greater increase in blood volume during breath-holding, indicating that blood could flow more easily through the widened vessels. The results were published in Biomedical Optics Express.

This device offers a simpler and more affordable way to assess stroke risk than current methods, which rely on costly imaging tests like MRI or CT scans. The SCOS technology is portable, making it suitable for use in primary care offices, emergency departments, community clinics, and even in developing countries. The research team plans to refine the device, integrate machine learning into data collection, and conduct a clinical trial with patient tracking over more than two years. They hope the device will eventually be used not only for stroke risk screening but also to pinpoint the location of a stroke that has already occurred.

"With this device, for the first time, we are going to have a way of knowing if the risk of someone having a stroke in the future is significant or not based on a physiological measurement," said Simon Mahler, a postdoctoral scholar in the lab of Changhuei Yang, the Thomas G. Myers Professor of Electrical Engineering, Bioengineering, and Medical Engineering at Caltech and a Heritage Medical Research Institute Investigator. "We think this can really revolutionize the way stroke risk is assessed and will eventually help doctors determine if a patient’s risk is stable or worsening." 

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