Soft Matter Physics
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Optical methods based on the absorption and scattering of near-infrared light are becoming increasingly important for the non-invasive detection and imaging of brain function in humans since they combine minimal radiation loads with high temporal resolution, functional specificity and portability [1]. The contrast mechanism of conventional near-infrared spectroscopy (NIRS) is based on neurovascular coupling, i.e. the changes of total hemoglobin concentration and oxygen saturation which accompany electrical activation of specific cortical areas. However, the diffuse propagation of light due to the strong scattering by inhomogeities within tissue hampers the spatial resolution of near-infrared imaging. Using multiple source-receiver pairs allows for mapping of cortical activity with centimeter resolution through the intact scalp and skull. Recent developments using time-of-flight detection allows to reduce signal contaminations from superficial layers, leading to significantly enhanced sensitivity to functional signals from the cortex [2-4].