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Measurements of optical properties (scattering coefficient [[mu].sub.s], absorption coefficient [[mu].sub.a], reduced scattering coefficient [[mu].sub.s]', and asymmetry factor g) have been carried out up to a volume particle concentration of [rho] = 0.227. The results for [[mu].sub.s] and [[mu].sub.s]' show significant deviations from the linear dependence on [rho] as expected when the independent scattering assumption is fulfilled. The asymmetry factor also changed significantly. In contrast, the dependence of [[mu].sub.a] remained linear even at the largest concentration investigated. The simple linear dependence of absorption on the chromophore concentration expected from the independent scattering assumption is thus applicable also to spectroscopic measurements of dense media. A comparison with an approximate theoretical model based on the Foldy-Twersky equation is also reported. The model provides a good description of the dependence of [[mu].sub.s] on particle concentration.

The method consists of measuring the perturbation provoked by a small volume of the diffusive medium on light propagating through a medium of known optical properties. The absorption and the reduced scattering coefficients of the medium are retrieved from multidistance continuous-wave measurements of transmittance. The inversion procedure is based on the solution of the diffusion equation obtained with a perturbative approach. The method has been validated with Monte Carlo results. Examples of experimental results are reported. OCIS codes: 160.4760, 290.7050, 290.1990, 170.5280, 170.6510.