Researchers from the University of Southern California (USC) and California Institute of Technology (Caltech) have created a straightforward, non-invasive method for measuring cerebral blood flow, which is now being adapted for clinical application.
Published on October 22, 2023, in the journal APL Bioengineering, this study outlines a device that utilizes a technique known as speckle contrast optical spectroscopy (SCOS), which has primarily been employed in animal studies until now. The device captures images of scattered laser light using an affordable, high-resolution camera.
Accurate measurement of cerebral blood flow is vital for addressing various neurological conditions such as strokes, traumatic brain injuries, and vascular dementia. Current techniques, including magnetic resonance imaging and computed tomography, tend to be expensive and not widely accessible.
Dr. Charles Liu, a clinical neurosurgery professor at USC”s Keck School of Medicine and director of the USC Neurorestoration Center, explains, “It”s that simple. Tiny blood cells pass through a laser beam, and the way the light scatters allows us to measure blood flow and volume in the brain.”
Initial human trials have already demonstrated the device”s effectiveness in assessing stroke risk and detecting brain injuries. In this latest research, Liu and his team aimed to verify that SCOS accurately measures blood flow within the brain rather than in the scalp, which also contains numerous blood vessels. This concern has long been an issue for researchers using light-based technologies to visualize brain activity.
The research team took an innovative approach by temporarily blocking blood flow to the scalp to confirm that SCOS readings were indeed reflecting signals from cerebral blood vessels. Their findings indicated that placing the detector at least 2.3 centimeters away from the laser source yielded the clearest measurements of cerebral blood flow.
Dr. Simon Mahler, a co-author of the study and an assistant professor in the biomedical engineering department at Stevens Institute of Technology, remarked, “This experimental evidence demonstrates for the first time in humans that a laser speckle optical device can penetrate beyond the scalp layers to access brain signals.” He added, “This is a significant step toward utilizing SCOS for non-invasive cerebral blood flow measurement.”
For years, researchers measuring brain signals with light-based technologies, such as lasers and fiber optics, have relied on statistical simulations to differentiate signals originating from the brain versus those from the scalp. The USC Neurorestoration Center team found a direct method to verify these differences through collaboration among surgeons, engineers, and neurologists.
Dr. Jonathan Russin, a neurosurgery professor at the University of Vermont and a continuing collaborator with the USC Neurorestoration Center, stated, “I perform surgeries to enhance cerebral blood flow, many of which involve temporarily disrupting blood flow to the scalp. This provided us with a straightforward means to test the technology: creating a change that specifically affected scalp circulation without impacting cerebral blood flow.”
During the study involving 20 participants, the team temporarily halted blood flow to the scalp and then collected a series of SCOS readings. By gradually moving the detector further from the head, they captured increasingly deeper signals from the brain. Their results confirmed that positioning the detector at a distance of 2.3 centimeters from the head allowed them to accurately measure cerebral blood flow while reducing scalp interference.
The findings underscore SCOS”s potential for non-invasively detecting cerebral blood flow and provide crucial guidance for other researchers working with light-based technologies, according to Liu. Beyond advancing research, the study affirms SCOS”s clinical potential for identifying and responding to strokes, brain injuries, and dementia.
Since all of the team”s research has been conducted with human subjects, the tool is poised for rapid transition from the laboratory to clinical practice. Some collaborators have already begun using the technique for diagnosing strokes and traumatic brain injuries. The research team will continue refining both the technology and the software, aiming to improve image resolution and the quality of data obtained from readings.
