Hybrid light method reveals how camera signals can probe blood flow in deeper tissues

Scientists have developed a hybrid light method that can identify how camera signals can probe blood flow in deeper tissues. This method combines interferometric near-infrared spectroscopy (iNIRS), which can distinguish signals based on the time light takes to travel through tissue, with camera-based systems that capture many more photons.

By analyzing the rate of changes in the speckle pattern formed when light passes through tissue, the researchers can calculate a blood-flow index, which measures the dynamics of circulation in the tissue being examined. The study involved two healthy men and used laser light with a wavelength of approximately 780 nm, which is in the near-infrared range.

The researchers positioned optical fibers 1 cm apart to deliver light into the tissue and collect it. When blood flow was measured optically at the forearm, the detector received mixed information from circulation in the scalp and deeper tissues. By separating light according to its time of flight, the researchers were able to increase the contribution of information from deeper regions, which helped distinguish signals from superficial circulation from blood flow in deeper tissues.

The study also showed that tight constriction of the headband restricted blood flow in the scalp, but late-arriving photons were less sensitive to this superficial compression, indicating that the index cannot independently confirm blood flow in a specific region of the brain.