Optical Properties of Human Brain Tissue, Meninges, and Brain Tumors in the Spectral Range of 200 to 900 nm

Abstract

Considering the increasing use of lasers in neurosurgery and the increasing number of wavelengths of laser light becoming available, we evaluated optical properties between 200 and 900 nm of meninges, normal human brain tissue, and brain tumors. We used a two-beam spectral photometer with an integrating sphere as the measuring instrument. The material consisted of 13 brains and 1 specimen each of dura mater, falx, and arachnoid obtained at autopsy and 30 samples of brain tumors removed during operation. In tissue samples more than 5 mm thick, the relative levels of absorption and scattering were estimated from the relative level of reflection measured according to the Kubelka-Munk theory. In thin tissue slices, penetration depth was calculated according to Beer's law from measurements of reflection and transmission. Generally, in all tissues there was an increase of reflection, scattering, and penetration depth and a decrease of absorption from the ultraviolet up to the near infrared spectral range interrupted by the absorption bands of hemoglobin. Within the ultraviolet spectral range, no major differences of optical properties were observed. Within the visible and near infrared spectral range, white matter reflected most of the incident power and showed the lowest level of absorption and the shortest penetration depth. Low grade gliomas revealed optical properties similar to those of gray matter. In comparison with normal brain tissue, meningiomas and glioblastomas showed significantly higher levels of absorption calculated according to the Kubelka-Munk theory from reflection measurements in thick tissue samples, but also deeper penetration obtained from measurements of reflection and transmission in thin slices, especially within the near infrared spectral range.