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Detection and characterization of absorbing inhomogeneities in biotissue by double-position CW optical-sensing technique with an optimal source-receiver separation

Potentialities of a double-position CW laser sensing technique with an optimal base are studied to detect absorbing inhomogeneities in turbid media at large optical depths. In the frame of the diffusion approximation, we have found the cross-section of an absorbing inhomogeneity in a turbid medium and derived approximate expressions for irradiance distribution, the spatial profile and contrast of the object and the optimal base length. 2D-images of the object were constructed. A system with rotated base is presented. It enables to extract useful component from detected signal by measuring modulation amplitude. We have performed laboratory experiments on laser sensing of a black object in a model turbid medium in the reflective and transilluminative regimes and proved the validity of our theory. The results of this work demonstrate feasibility of the double-position CW laser sensing technique with the optimal source-receiver separation to detect and characterize absorbing inhomogeneities in biotissues at a depth of several photon transport mean free paths. We expect that this technique can be effectively applied to bioimaging to monitor in vivo the internal structure of the human tissue.