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In vivo study on NIR light propagation in the human head

Priya Karthikeyana*1, Ulriika Honkaa1, Martti Ilvesmäkia2, Hany Ferdinandoa2,
Vesa Korhonen 1, and Teemu Myllyläa1,2

1University of Oulu, Research Unit of Medical Imaging, Physics and Technology, Oulu, Finland
2University of Oulu, Optoelectronics and Measurement Techniques Unit, Oulu, Finland

Abstract

Near-infrared spectroscopy (NIRS) techniques in brain imaging utilize the spectrum range approximately between 650 nm to 1100 nm, where light attenuation in tissue is low enough to enable reaching the cerebral cortex of the brain. In these studies, particularly oxygenation changes in the cerebral cortex are of great interest, since the concentrations of oxyhaemoglobin and deoxyhaemoglobin change due to coupling of hemodynamics to cortical neural activity. There are numerous simulation and phantom studies that show NIR light can penetrate into brain tissue to a depth of approximately 1–2 cm, and by increasing the source-detector distance, illuminating light penetrates deeper into brain tissue. This paper studies, probably for the first time, light propagation in the human head using in vivo technique. For this, we studied anatomy of 15 human heads in magnetic resonance imaging (MRI), particularly the thickness and morphology of the tissue layers of skin, skull, CSF, and measured from these positions absorbance of NIR range of 650 nm to 1100 nm at source-detector distances of 10 mm to 30 mm using commercial spectrometer.
Keywords: NIRS, brain, light propagation, MRI


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Priya Karthikeyan
University of Oulu
Finland

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