Multi-channel multi-distance broadband near-infrared spectroscopy system to measure the spatial response of cellular oxygen metabolism and tissue oxygenation.

We present a multi-channel, multi-distance broadband near-infrared spectroscopy (NIRS) system with the capability of measuring changes in haemoglobin concentrations (Δ[HbO], Δ[HHb]), oxidation state of cytochrome-c-oxidase (Δ[oxCCO]) and tissue oxygen saturation (TOI) in the adult human brain. The main components of the instrument are two customized spectrographs and two light sources. Each spectrograph is lens-based to improve light throughput, has a grating enhanced to optimise reflection in the near-infrared (NIR) spectral region and uses a front illuminated cooled CCD camera (-70° C) with a square chip dimension of 12.3 x 12.3 mm (512 x 512 pixels). Each light source uses a 50W halogen bulb with a gold plated mirror to increase the intensity of the NIR light. Each light source was connected to a custom-built bifurcated fibre bundle to create two source fibre bundles (3.2 mm diameter each). Each spectrograph received light input from another custom-built fibre bundle comprised of six individual bundles (one with 0.6 mm diameter and the other five with 1.5 mm diameter). All fibre bundles were fixed on a 3D printed optode holder (two light sources x two fibre bundles each = four probes; and two spectrographs x six fibre bundles each = 12 probes) that allowed 24 multi-distance channels across the forehead (six channels at 20 mm, three channels at 30 mm and 15 channels at 35 mm) and six TOI measurements. We demonstrated the use of the system in a cohort of nine healthy adult volunteers during prefrontal cortex functional activation using the Stroop task. We have observed functional responses identified as significant increase in Δ[HbO], decrease in Δ[HHb] and increase in Δ[oxCCO] in five channels (out of 12), that overlay the left and right dorsolateral prefrontal cortices. There was no observable TOI functional response and we have shown small variations in TOI across different sites within the same subject and within the same site across subjects.