Near-infrared light propagation in an adult head model I Modeling of low-level scattering in the cerebrospinal fluid layer

Abstract

Adequate modeling of light propagation in a human head is important for quantitative near-infrared spectroscopy and optical imaging. The presence of a nonscattering cerebrospinal fluid (CSF) that surrounds the brain has been previously shown to have a strong effect on light propagation in the head. However, in reality, a small amount of scattering is caused by the arachnoid trabeculae in the CSF layer. In this study, light propagation in an adult head model with discrete scatterers distributed within the CSF layer has been predicted by Monte Carlo simulation to investigate the effect of the small amount of scattering caused by the arachnoid trabeculae in the CSF layer. This low scattering in the CSF layer is found to have little effect on the mean optical path length, a parameter that can be directly measured by a time-resolved experiment. However, the partial optical path length in brain tissue that relates the sensitivity of the detected signal to absorption changes in the brain is strongly affected by the presence of scattering within the CSF layer. The sensitivity of the near-infrared signal to hemoglobin changes induced by brain activation is improved by the effect of a low-scattering CSF layer.

In-vivo multilaboratory investigation of the optical properties of the human head

“…For this evident reason the present study, based on measurements obtained with different types of instrumentation, is a contribution to filling in the gap existing between the present knowledge and the actual values of the optical properties of the head. This uncertain knowledge can be also noted in the numbers for the optical properties used in the forward models developed for the head and proposed in tissues optics that show a large spread of values through the years [11,12,24,26,38,44,[47][48][49]. Thus, a better knowledge of the optical properties of the head would help to improve the modelling of photon migration for applications of near infrared light for the head.…”

“…A 3-layer laterally-infinite medium was simulated using two combinations of reduced scattering and thicknesses (Table 2). Reduced scattering values are taken from the values at 830 nm of the measurements discussed in section 6 and thicknesses are derived from literature [11,12,44]. Homogeneous refractive index (1.4) and anisotropy factor (0.8) have been fixed.…”

“…Light propagation is strongly affected by this heterogeneity. In particular the CSF has been object of a lot of investigations due to its "light guiding" effect depending on its transparency [9] and to its reticular structure composed by arachnoids that can strongly affect the scattering of light [10][11][12].…”

Motor imagery in response to fake feedback measured by functional near-infrared spectroscopy

“…General reasons for these individual variability may be effects of anatomical variance such as thickness of the skull and cerebrospinal fluid layers (Okada and Delpy 2003a;Okada and Delpy 2003b). However, this does not explain why variability is prominent during MI tasks following positive or negative feedback and low during without feedback or ME.…”

Characteristics of Cortical Activation in Schizophrenia during the Card Game ^|^ldquo;Concentration^|^rdquo;

“…We defined each measurement area between probes as a channel (ch). The NIRS machine is thought to measure changes at points 2 to 3 cm beneath the scalp, that is, the cerebral cortical surface [25,26]. The lowest anterior probes, right ch 22 and left ch 19, were positioned along the Fp1-Fp2 line according to the International 10-20 system used in electroencephalography (Fig.…”