Absolute optical values for the human adult brain are difficult to measure due to the layered structure of head. We used long-range multi-distance frequency-domain near-infrared spectroscopy (NIRS) to measure absolute optical values of each tissue layer in the human head. We determined baseline optical values for the forehead in 30 adults (age range 21 to 50). We found that tissue oxygenation was relatively narrowly distributed (STD~3%) within the subject group, whereas hemoglobin concentrations and optical parameters had a relatively broader distribution. In addition, the distance dependence of optical and physiological parameters showed the layered structure of the human head. These measurements allowed determination of absolute optical properties in each layer of the adult head.

© 2002 Optical Society of America

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