Hybrid Light Technique Tracks Deep Blood Flow Inside Living Tissue
Researchers at ICTER combine interferometry and high-speed cameras to distinguish surface vessels from cerebral circulation.
Optical sensors placed against human skin often struggle to separate superficial blood flow from circulation inside deeper organs. To overcome this limitation, researchers at the International Centre for Translational Eye Research have developed a hybrid near-infrared optical system that isolates signals from deeper tissue layers. The medical device innovation, tested on human volunteers, provides a non-invasive way to track blood dynamics without surgical intervention.
Resolving the depth puzzle in optical tissue monitoring
When clinicians shine light on the forehead to monitor cerebral circulation, the returning signal is contaminated by blood moving through the scalp. Conventional interferometric near-infrared spectroscopy can distinguish signals based on the time light takes to travel through tissue, but it gathers very few photons, as reported by MedicalXpress. Standard camera-based detection captures far more light, yet it fails to retain time-of-flight information when living tissue changes rapidly. To merge the advantages of both approaches, Marcin Marzejon and Dawid Borycki built a hybrid optical instrument, an innovation that pairs laser interferometry with camera detection.
“Time of flight helps us select light with a greater contribution from deeper tissues. When we combine this information with changes caused by blood-cell motion, we can better distinguish signals from superficial circulation from blood flow in deeper tissues.”
— Dawid Borycki, leader of the PICO group at ICTER
Tracking speckle patterns with 780-nanometer laser light
The system uses a laser operating at a wavelength of approximately 780 nm in the near-infrared range, split into complementary measurement paths fed by a single light source. As the beam travels through biological tissue, it scatters repeatedly and forms a grainy distribution of light and dark spots called a speckle pattern on the sensor. Moving red blood cells alter this pattern over time, allowing the software to compute a blood-flow index that reflects circulatory speed, according to MedicalXpress. Photons taking longer paths through deeper structures arrive later at the detector, enabling the prototype setup to differentiate deep physiological responses from superficial skin flow.
Validating depth sensitivity on forearms and foreheads
The researchers demonstrated the technique on two healthy men aged 33 and 43, placing optical fibers 1 cm apart on the skin during tests recorded in one-second trials. During a forearm experiment, inflating a blood pressure cuff halted blood flow and slowed speckle changes, followed by an immediate surge above baseline once pressure was released, as detailed by MedicalXpress. In that reactive hyperemia phase, late-arriving photons displayed a much stronger signal increase than early-arriving photons. A separate test using an elastic headband on the forehead confirmed that late-arriving light showed a weaker response to surface scalp compression, verifying its sensitivity to deeper layers and highlighting the clinical potential of the invention.
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