Hyperspectral Near-Infrared Spectroscopy for the Clinical Monitoring of the Brain: Can We Measure the Brain of Patients Experiencing Severe Changes in the Entire Body?

Near Infrared Spectroscopy (NIRS) uses near infrared light to measure the concentrations of different tissue chromophores such as oxygenated hemoglobin (HbO2), deoxygenated hemoglobin (HHb), and cytochrome c oxidase (Cyt-ox). However, NIRS measurements in adult humans are highly sensitive to extracranial tissue layers and thus less sensitive to the brain. The aim of this work was to assess the effectiveness of measuring specific brain hemodynamic response during breath-holding respiratory challenge. We used hyperspectral NIRS with combined short and long source-detector distance channels at 1 cm, 3 cm, and 4 cm. We used two approaches for signal processing: we measured the absolute hemoglobin concentrations using the analytical solution to the light diffusion equation for the semi-infinite homogeneous medium, and the changes in tissue layers using the modified Lambert-Beer law for a two-layer medium. Linear regression in the time domain of long distance and short distance channel signals allowed us to assess differences in brain responses and extracranial changes. We found that using the short-range channel was important for measuring cerebral response to breath-holding. We also found that the optimal wavelength band was between 750 and 900 nm, with the largest partial change between 800 and 850 nm. We also found that Cyt-ox at the 4 cm channel exhibited the most brain-specific changes compared to HbO2 and HHb.