Oxygen saturation estimation in brain tissue using diffuse reflectance spectroscopy along stereotactic trajectories.

Diffuse reflectance spectroscopy (DRS) can be used to estimate oxygen saturation (SO₂) of hemoglobin and blood fraction (f_B) in brain tissue. The aim of the study was to investigate the SO₂ and f_B in different positions along deep brain stimulation (DBS) trajectories and in specific target regions using DRS and a novel algorithm. DRS measurements were done at 166 well-defined anatomical positions in relation to stereotactic DBS-implantation along 20 trajectories toward 4 DBS targets (STN, Vim, GPi and Zi). The measurements were dived into groups (gray, white and light gray matter) related to anatomical position, and DBS targets, before comparison and statistical analysis. The median SO₂ in gray, white and light gray matter were 52%, 24% and 20%, respectively. Median f_B in gray matter (3.9%) was different from values in white (1.0%, p < 0.05) and light gray (0.9%, p < 0.001) matter. No significant difference in median SO₂ and f_B was found between DBS target regions. The novel algorithm allows for quick and reliable estimation of SO₂ and f_B in human brain tissue.