Abstract
.Significance: Functional near-infrared spectroscopy (fNIRS) is a technique for detecting regional hemodynamic responses associated with neural activation in the cerebral cortex. The absorption changes due to hemodynamic changes in the scalp cause considerable signal contamination in the fNIRS measurement. A method for extracting hemodynamic changes in the cerebral tissue is required for reliable fNIRS measurement.Aim: To exclusively detect cerebral functional hemodynamic changes, we developed an fNIRS technique using reflectance modulation of the scalp surface.Approach: The theoretical feasibility of the proposed method was proven by a simulation calculation of light propagation. Its practical feasibility was evaluated by a phantom experiment and brain activation simulation mimicking human fNIRS experiments.Results: The simulation calculation revealed that the partial path length of the scalp was changed by reflectance modulation of the scalp surface. The influence of absorption change in the superficial layer was successfully reduced by the proposed method, using only measurement data, in the phantom experiment. The proposed method was applicable to human experiments of standard designs, achieving statistical significance within an acceptable experimental time-frame.Conclusions: Removal of the scalp hemodynamic effect by the proposed technique will increase the quality of fNIRS data, particularly in measurements in neonates and infants that typically would require a dense optode arrangement.
Highlights
Functional near-infrared spectroscopy is a relatively simple technique for detecting the regional hemodynamic response associated with neural activation in the cerebral cortex
The simulation calculation revealed that the partial path length of the scalp was changed by reflectance modulation of the scalp surface
Removal of the scalp hemodynamic effect by the proposed technique will increase the quality of Functional near-infrared spectroscopy (fNIRS) data, in measurements in neonates and infants that typically would require a dense optode arrangement
Summary
Functional near-infrared spectroscopy (fNIRS) is a relatively simple technique for detecting the regional hemodynamic response associated with neural activation in the cerebral cortex. Compared to other elaborate functional neuroimaging techniques, such as functional magnetic resonance imaging and positron-emission tomography, fNIRS has the advantages of low risks, as it does not involve exposure to a magnetic field or radiation, hardware portability, tolerance for electromagnetic noise, and lower running cost These advantages of fNIRS have increased its use in various disciplines, but some technical concerns in fNIRS have remained, which have not been disclosed to such users.[1,2] These technical concerns include its sparser sampling than the localization of cerebral functions,[3] the variation in noise with hair coverage,[4] optode artifacts,[5,6,7] and the influence of scalp blood flow changes.[8,9,10,11,12]. A method for extracting optical property changes in the cerebral tissue layer is required for reliable fNIRS measurement
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