In vivo study on NIR light propagation in the human head

Karthikeyan, Priya; Honka, Ulriika; Ilvesmäki, Martti; Ferdinando, Hany; Korhonen, Vesa; Myllylä, Teemu

doi:10.1117/12.2626380

Cited by 1 publication

(1 citation statement)

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“…Figure 1. Spectral changes due to changes in dura + CSF thickness, previously also studied in 6 . In the selected group of volunteers, all subjects had approximately same skin and skull layer thicknesses, but CSF layer thickness variation between 1 mm -9 mm.…”

Section: Resultsmentioning

confidence: 99%

Dynamics of human cerebral fluids measured by near-infrared spectroscopy

Myllylä¹,

Ilvesmäki²,

Moradi³

et al. 2023

Dynamics and Fluctuations in Biomedical Photonics XX

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Obtaining parameters that characterize cerebral fluid interactions in the human brain is of high interest particularly as regards studies of the glymphatic system and in relation to neurodegeneration diseases. Near-infrared spectroscopy (NIRS) based techniques commonly measure cerebral hemodynamics using a combination of wavelengths approximately between 650 nm and 950 nm, where light is to a lesser amount attenuated by water, enabling light to reach the brain. By adding a wavelength that is dominantly absorbed by water, while still penetrating below skull, we may have a possibility to measure also cortical water concentration changes, particularly dynamics of the cerebrospinal fluid (CSF) volume, which have been connected to brain's waste removal system. In this study, we show based on in vivo human experiments that small dynamical variations in the CSF layer, between the human skull and brain cortex determined by MRI, correlate with nearinfrared (NIR) light intensity changes particularly above 960 nm when measured at long (> 3 cm) source-detector distance. In addition, based on the previously reported anti-correlation between total haemoglobin (HbT) and water signal fluctuations measured with NIRS, we further investigated the differences in the anti-correlations when using short (< 2 cm) and long source-detector distances. In general, at a short source-detector distance the NIRS measurement volume does not reach a depth below human skull. In consequence, our results from 12 healthy subjects show greater anti-correlation between HbT and water when using a long source-detector distance, supporting the idea that NIRS can be used to monitor also human cortical water fluctuations non-invasively.

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Section: Resultsmentioning

confidence: 99%