A new, non-invasive method of measuring cerebral blood flow with light has been developed by biomedical engineers and neurologists at the University of California, Davis and used to detect brain activation. The new method, functional interferometric scattering wave spectroscopy, or fiDWS, promises to be less expensive than existing technology and could be used to assess brain damage or in neuroscience research. The work was published on May 12 in Scientific progress.
“We can now assess how well the brain regulates blood flow, and even detect brain activation non-invasively in adult humans, using principles similar to functional magnetic resonance imaging (fMRI), but at a fraction of the cost, ”said Vivek Srinivasan, associate associate professor of biomedical engineering at UC Davis and lead author of the study.
The human brain makes up 2% of our body weight, but takes 15% to 20% of the blood flow from the heart. Measuring cerebral blood flow is important for diagnosing stroke and for predicting secondary damage in subarachnoid hemorrhages or traumatic brain injury. Physicians who provide intensive neurological care would also like to monitor a patient’s recovery by imaging cerebral blood flow and oxygenation.
Existing technology is expensive and cannot be applied continuously or at the bedside. For example, current cerebral blood flow imaging techniques require expensive MRI or CT scans. There are light-based technologies, such as near infrared spectroscopy, but these also have disadvantages in terms of accuracy.
The new method takes advantage of the fact that near infrared light can penetrate through body tissue. If you shoot a near infrared laser on someone’s forehead, the light will be scattered several times by tissues, including blood cells. By picking up the fluctuating signal of light coming back out of the skull and scalp, you can get information about the blood flow inside the brain.
Of course, this signal is extremely weak. Srinivasan and postdoctoral researcher Wenjun Zhou overcame this problem by using interferometry: the ability of light waves to overlap, strengthen, or cancel each other out. In particular, thanks to interferometry, a strong light wave can amplify a weak light wave by increasing its detected energy.
Activation of the prefrontal cortex
They first divided the laser beam into “sample” and “reference” paths. The sample beam enters the patient’s head and the reference beam is routed so that it reconnects with the sample beam before going to the detector. Through interferometry, the stronger reference beam amplifies the weak sample signal. This allowed the team to measure the output with the type of light-sensing chip found in digital cameras, instead of expensive photon-counting detectors. They then use software to calculate a blood flow index for different places in the brain.
Srinivasan and Zhou worked with Dr Lara Zimmerman, Dr Ryan Martin and Dr Bruce Lyeth in the Department of Neurological Surgery at UC Davis to test the technology. They found that with this new technology, they could measure blood flow faster and deeper below the surface than with current light-based technology. They could measure pulsating cerebral blood flow and could also detect changes when volunteers were given a slight increase in carbon dioxide.
When the volunteers were faced with a simple math problem, the researchers were able to measure the activation of the prefrontal cortex across the forehead.
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Material provided by University of California – Davis. Original written by Andy Fell. Note: Content can be changed for style and length.