Near-infrared light propagation in an adult head model II Effect of superficial tissue thickness on the sensitivity of the near-infrared spectroscopy signal

Abstract

It is important for near-infrared spectroscopy (NIRS) and imaging to estimate the sensitivity of the detected signal to the change in hemoglobin that results from brain activation and the volume of tissue interrogated for a specific source-detector fiber spacing. In this study light propagation in adult head models is predicted by Monte Carlo simulation to investigate the effect of the superficial tissue thickness on the partial optical path length in the brain and on the spatial sensitivity profile. In the case of source-detector spacing of 30 mm, the partial optical path length depends mainly on the depth of the inner skull surface whereas the spatial sensitivity profile is significantly affected by the thickness of the cerebrospinal fluid layer. The mean optical path length that can be measured by time-resolved experiments increases when the skull thickness increases whereas the partial mean optical path length in the brain decreases when the skull thickness increases. These results indicate that it is not appropriate to use the mean optical path length as an alternative to the partial optical path length to compensate the NIRS signal for the difference in sensitivity caused by variation of the superficial tissue thickness.

Measuring tissue hemodynamics and oxygenation by continuous-wave functional near-infrared spectroscopy—how robust are the different calculation methods against movement artifacts?

“…This feature is particularly of interest for the detection of task-evoked brain activity (i.e. the hemodynamic response) which is accompanied by changes in hemodynamics in the superficial tissue too (Gagnon et al 2012, Kirilina et al 2012, Klaessens et al 2004, Okada and Delpy 2003. Compared to the other MD methods, MD method 3 (i.e.…”

In-vivo multilaboratory investigation of the optical properties of the human 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.…”

Near-Infrared Spectroscopy

“…Changes in the thickness of the CSF layer alter the intensity of detected light, therefore any brain movement and expansion during the measurement would affect the NIRS signal. The optical path length in the brain for a certain inter-optode distance depends to a great extent on the thickness of the skull whereas the thickness of the CSF layer scarcely affects the optical path-length in the brain (Okada & Delpy, 2003).…”