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Development of optical mammography based on analysis of time-resolved photon path distribution

A diffused optical mammography composed of a 48-channel time-resolved spectroscopy system is being developed for breast cancer diagnosis. The system utilizes the time-correlated single photon counting method, and the detector modules and the signal processing circuits were custom made to obtain a high signal to noise ratio and high temperature stability with a high temporal resolution. Pulsed light generated by a Ti:Sapphire laser was irradiated to the breast, and the transmitted light was collected by optical fibers placed on the surface of a hemispherical gantry filled with an optical matching fluid. To reconstruct a 3D image of the breast, we employed a method using time-resolved photon path distribution (time-resolved PPD) based on the assumption that scattering and absorption are independent of each other. As it is not necessary to recalculate the time-resolved PPD corresponding to any changes in the absorption, we can obtain the reconstructed image quickly. The clinical research was started in January 2007. In a comparative study with conventional modalities, the breast cancers were detected as optically higher absorption regions. Moreover, it was suggested that the optical mammography is useful in monitoring the effect of chemotherapy.