Neurotechnology company Kernel has developed a wearable headset device for brain measurement. The device, called Kernel Flow, is based on time-domain functional near-infrared spectroscopy (TD-fNIRS) — considered the gold standard for noninvasive optical brain imaging devices. In validation tests, results from Kernel Flow were comparable to those yielded by traditional TD-fNIRS systems. TD-fNIRS enables accurate, high-resolution measurement of the brain and its functions by emitting picosecond pulses of light into tissue and measuring the arrival times of single photons. The distribution of photon arrival times estimates the tissue’s optical properties. The photon arrival times can also be used to localize changes in deeper tissue by analyzing the late-arriving photons or the moments of the time-of-flight (ToF) distribution. However, TD-fNIRS systems are also bulky, expensive, and complex. The Kernel Flow headset, which weighs about 4.5 pounds, features a miniaturized design that could encourage broader application of TD-fNIRS for brain imaging, its developers said. Kernel Flow comprises 52 modules arranged in four plates that fit on either side of the head. The modules cover the frontal, parietal, temporal, and occipital cortices. Each module consists of a central dual wavelength laser source (690 and 850 nm), surrounded by six detectors. Light is transmitted from source to detector through spring-loaded light pipes. The Kernel Flow headset. The FDA recently authorized a study using the Kernel Flow system to measure the psychedelic effect of ketamine on the brain. Courtesy of Kernel. The spacing between plates can be controlled using spacers that can be adjusted based on the user’s head size and the regions of interest. The modules provide dense channel coverage over the entire head. The two laser sources in each module generate laser pulses less than 150 picoseconds wide. The photons are then reflected off a prism and combined in the source light pipe, which directs the beam to the scalp. After passing through the scalp, the laser pulses are captured by six detector light pipes and then transmitted to the six detectors. Each detector is located 10 mm from the laser source. The detectors record the photon arrival times into histograms and are capable of handling high photon count rates (i.e., rates exceeding 1 × 109 counts per second). Kernel Flow’s optics are designed to serve multiple objectives: coupling the source laser light from the lasers to the scalp, capturing return light from the scalp, conforming to head curvature, mitigating interference from hair, isolating detected signals between detectors, and maintaining a stable intensity at the detector locations. The research team characterized Kernel Flow using standard protocols and, to demonstrate the system’s performance, used Kernel Flow to record the brain signals of two participants who performed a finger-tapping task. During these tests, histograms from more than 2000 channels across the brain were collected to measure changes in the concentrations of oxyhemoglobin and deoxyhemoglobin. The system performed well in both the characterization protocols and in localizing brain activation in humans during the finger-tapping task. The FDA recently authorized a study using the Kernel Flow system to measure the psychedelic effect of ketamine on the brain, and the system was developed for scalable manufacturing to allow for inexpensive commercial production. Further, the next generation of noninvasive optical brain imaging devices could begin with the Kernel Flow headset, according to Dimitris Gorpas, group leader at Helmholtz Zentrum Munich and guest editor at the Journal of Biomedical Optics. “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,” Gorpas said. “I am really looking forward to what the brain has yet to reveal.” Ryan Field, CTO of Kernel, said that while the test results are promising, more testing is needed because 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,” Field said. The research was published in the Journal of Biomedical Optics (www.doi.org/10.1117/1.JBO.27.7.074710).