Laser-Doppler flow measurements with penetration depths from 10 to 30 mm have been performed on a layered model of the human head consisting of a regular array of capillaries with diameters of 340 microm embedded in an epoxy matrix with tissuelike scattering and absorption properties. Monte Carlo simulations and an analytical approach based on diffusing wave spectroscopy have corroborated the measurements and have led to a quantitative description of flow in deep-lying tissue layers with regard to layers near the surface also. The results indicate that it may be possible to measure changes in cortical blood flow even in the presence of a well-perfused scalp.

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Laser Doppler flow measurements on biological tissuelike phantoms have shown that penetration depths of 30 mm could be obtained, thus exceeding the penetration depth of commercial instruments for the measurement of skin perfusion by more than an order of magnitude. Monte Carlo simulations were performed and compared with measurement results obtained on a headlike tissue model to quantify the influence of perfusion of the scalp on the cortex perfusion results. We found Doppler frequency spectra to be independent of the mean scattering angle and could be fitted with a sum of Gaussian functions, using a simple analytical model.

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