Recent advances in brain imaging techniques facilitate accurate, high-resolution obser­vations of the brain and its functions. For example, functional near-infrared spectro­scopy (fNIRS) is a widely used noninvasive imaging technique that employs near-infrared light to determine the relative concentration of hemoglobin in the brain, via differences in the light absorption patterns of hemoglobin. Most noninvasive brain scanning systems use continuous-wave fNIRS, where the tissue is irra­diated by a constant stream of photons. However, these systems cannot differen­tiate between scattered and absorbed photons. A recent advancement to this technique is time-domain (TD)-fNIRS, which uses picosecond pulses of light and fast detectors to estimate photon scattering and absorption in tissues. However, such systems are expensive and complex and have a large form factor, limiting their widespread adoption.

To overcome these challenges, researchers from Kernel, a neuro­technology company, developed a wearable headset based on TD-fNIRS technology. This device – Kernel Flow – weighs 2.05 kilograms and contains 52 modules arranged in four plates that fit on either side of the head. The headset modules feature two laser sources that generate laser pulses less than 150 pico­seconds wide. The photons are then reflected off a prism and combined in a source light pipe that directs the beam to the scalp. After passing through the scalp, the laser pulses are captured by six spring-loaded detector light pipes that are 2 millimeter in diameter and then trans­mitted to six hexagonally arranged detectors 10 millimeter away from the laser source. The detectors record the photon arrival times into histograms and are capable of handling high photon count rates.

To demonstrate its perfor­mance, the Kernel Flow system was used to record the brain signals of two parti­cipants who performed a finger-tapping task. During the testing session, histograms from more than 2,000 channels were collected from across the brain to measure the changes in the concen­trations of oxyhemo­globin and deoxyhemo­globin. The system was found to match conventional TD-fNIRS systems. “We demonstrated a performance similar to benchtop systems with our miniaturized device as charac­terized by standardized tissue and optical phantom protocols for TD-fNIRS and human neuro­science results,” explains Ryan Field, the Chief Techno­logy Officer at Kernel.

While the results are promising, Field acknow­ledges the need for more testing as near-infrared light is absorbed dif­ferently by certain hair and skin types. “We are currently collecting data with Kernel Flow to demonstrate additional human neuro­science applications. We are also in the process of evaluating the performance of the system with different hair and skin types,” he says. Kernel Flow packages large-scale TD-fNIRS systems into a wearable form, delivering the next generation of noninvasive optical brain imaging devices. Systems like Kernel Flow will make neuro­imaging much more accessible, to enable widespread benefits in health and science. For instance, the FDA recently authorized a study using the Kernel Flow system to measure the psyche­delic effect of ketamine on the brain.

Dimitris Gorpas of Helmholtz Zentrum Munich, a German research center for environ­mental health, remarks, “This is the world's first wearable full-head coverage TD-fNIRS system that maintains or improves on the per­formance of existing benchtop systems and has the potential to achieve its mission of making neuro measure­ments mainstream. I am really looking forward to what the brain has yet to reveal.” (Source: SPIE)

Reference: H. Y. Ban et al.: Kernel Flow: a high channel count scalable time-domain functional near-infrared spectroscopy system, J. Biomed. Opt. 27, 074710 (2022); DOI: 10.1117/1.JBO.27.7.074710

Link: Kernel, Culver City, USA