A method for monitoring of oxygen saturation changes in brain tissue using diffuse reflectance spectroscopy

Continuous measurement of local brain oxygen saturation (SO₂ ) can be used to monitor the status of brain trauma patients in the neurocritical care unit. Currently, micro-oxygen-electrodes are considered as the "gold standard" in measuring cerebral oxygen pressure (pO₂ ), which is closely related to SO₂ through the oxygen dissociation curve (ODC) of hemoglobin, but with the drawback of slow in response time. The present study suggests estimation of SO₂ in brain tissue using diffuse reflectance spectroscopy (DRS) for finding an analytical relation between measured spectra and the SO₂ for different blood concentrations. The P₃ diffusion approximation is used to generate a set of spectra simulating brain tissue for various levels of blood concentrations in order to estimate SO₂ . The algorithm is evaluated on optical phantoms mimicking white brain matter (blood volume of 0.5-2%) where pO₂ and temperature is controlled and on clinical data collected during brain surgery. The suggested method is capable of estimating the blood fraction and oxygen saturation changes from the spectroscopic signal and the hemoglobin absorption profile.