A new technique could allow clinicians and scientists to measure blood flow within the brain using beams of light.
A process known as functional magnetic resonance imaging (fMRI) already allows non-invasive monitoring of blood flow in the brain, but the new light-based system could achieve similar results at a fraction of the cost and with less specialised equipment.
MRI and CT scanners are very expensive and cannot be used continuously or at a patient’s bedside.
Measuring this cerebral blood flow is important for assessing brain injuries and diagnosing strokes and could help advance neuroscientific research.
The new technique, known as functional interferometric diffusing wave spectroscopy (fiDWS), was detailed in the journal Science Advances.
It makes use of the fact that human body tissue can be penetrated by a light that is close to infrared on the spectrum.
When a near-infrared light is directed onto the forehead, the light beam will be scattered numerous times as it passes through the tissues and blood cells.
Information about the blood flow inside the brain can be gathered by monitoring the fluctuation of the light that makes its way back out through the patient’s head.
This signal tends to be very weak, but the researchers, from the University of California, Davis (UCD), overcame this challenge using a technique called interferometry.
Scientists used interferometry to boost the signal
The technique uses the phenomenon of interference of waves and can be used with radio or sound as well as light waves.
One of the options is to boost a weak light wave by using a stronger one to increase its detected energy.
The team split the laser beam into two paths, with a ‘sample’ beam being directed into the patient’s head.
Meanwhile, a reference beam is routed to reconnect with the first beam before it reaches the receiver, boosting the weaker signal from the sample beam as it leaves the skull.
The boosted signal is strong enough to measure with the kind of light-detection chip used in digital cameras, rather than needing specialist photon-counting equipment.
Once the signal is collected, special software is used to create an index of blood flow for different parts of the brain.
In tests, researchers were able to measure blood flow within the brain and detect changes when volunteers were subjected to a small increase in carbon dioxide.
They were also able to detect brain activity, noting the activation of the prefrontal cortex when volunteers were given a simple maths problem to solve.
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