Investigating the Vis-NIR Spectral and Structural Properties of the Cerebral Cortex in Human Brain Tissues

Abstract

The objective of the study is to measure the optical properties of gray matter in the cerebral cortex in a spectral range of 400–1100 nm, including attenuation coefficients, scattering coefficients, scattering efficiency, and estimates of the penetration depth for optical imaging. The study aims to identify absorption peaks and investigate structural properties, such as neuron density, using Beer's law and the Mie model. The findings contribute to developing noninvasive diagnostic imaging techniques and therapies in the near-infrared (NIR) range for the cerebral cortex in the human brain. Gray matter in the outermost layer of the cerebral cortex plays a significant role in information processes, such as reasoning and planning, in addition to influencing intelligence, emotion, memory, and language. In this paper, measurements of the optical properties, such as the attenuation coefficients, scattering coefficients, scattering efficiency, and the penetration depth of gray matter in the cerebral cortex were measured in the fresh brain tissue of a healthy human male at a spectral range of 400–1100 nm. Determining the optical properties of gray matter is important for developing NIR noninvasive diagnostic imaging techniques and therapies. The absorption spectra of the gray matter tissues obtained here showed clear peaks at 550 and 580 nm due to oxyhemoglobin (HbO₂) and at 970 nm due to water. The possible NIR optical imaging depth was roughly 3.8 mm at 800 nm, determined by the theoretical limit resulting from ballistic and snake photons. Using Beer’s law and the Mie model, structural properties (e.g., neuron density) in the gray matter of human brain tissue were investigated for the first time. The density of neurons in the examined gray matter tissue sample was estimated as roughly 40,000 neurons/mg. In addition, an extensive investigation is performed and a summary of optical properties, including scattering coefficients and transport length, for both gray and white matter in the human cerebral cortex, is outlined based on existing literature. The study will particularly emphasize examining the maximum distance light can traverse and the depth at which it can effectively penetrate, which facilitates noninvasive imaging of neurons in deep tissue regions. Recent techniques from the literature are explored that highlight structural changes in the normal brain, aging, and neurodegenerative diseases.