Intracerebral quantitative chromophore estimation from reflectance spectra captured during deep brain stimulation implantation.

Quantification of blood fraction (f(blood)), blood oxygenation (S(O2)), melanin, lipofuscin and oxidised and reduced Cytochrome aa 3 and c was done from diffuse reflectance spectra captured in cortex, white matter, globus pallidus internus (GPi) and subthalamus during stereotactic implantations of 29 deep brain stimulation (DBS) electrodes with the aim of investigating whether the chromophores can give physiological information about the targets for DBS. Double-sided Mann-Whitney U-tests showed more lipofuscin in GPi compared to white matter and subthalamus (p < 0.05). Compared to the other structures, f(blood) was significantly higher in cortex (p < 0.05) and S(O2) lower in GPi (p < 0.05). Median values and range for f(blood) were 1.0 [0.2-6.0]% in the cortex, 0.3 [0.1-8.2]% in white matter, 0.2 [0.1-0.8]% in the GPi and 0.2 [0.1-11.7]% in the subthalamus. Corresponding values for S(O2) was 20 [0-81]% in the cortex, 29 [0-78]% in white matter, 0 [0-0]% in the GPi and 0 [0-92]% in the subthalamus. In conclusion, the measurements indicate very low oxygenation and blood volume for DBS patients, especially in the GPi. It would be of great interest to investigate whether this is due to the disease, the normal situation or an artefact of doing invasive measurements.