Imaging objects in tissuelike media with optical tagging and the diffuse photon differential transmittance.

In a proof-of-concept experiment, we optically tagged objects embedded in an inhomogeneous and multiple-scattering medium and measured the difference between the transmitted diffuse photons at two optical wave-lengths, one at and the other off a sharp absorption peak of the exogenous contrast agent. We demonstrated that the visibility of tagged objects was significantly enhanced in comparison with that of untagged objects. From our analysis it seems possible to use dual-wavelength differential transmittance spectrometry together with monoclonal-antibody-delivered optical contrast agents to detect tumors as small as 0.1-0.3 cm in size and embedded as deeply as a few centimeters beneath a tissue surface.