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Monte Carlo modeling of time-resolved near-infrared transillumination of human breast tissue

A Monte Carlo method is used to model the propagation of near infrared light in human breast tissue. The corresponding scattering coefficient, g-factor, and absorption coefficient of the model are adjusted to fit the temporal point spread function. With this model the dependence of the spatial resolution as a function of absorption, thickness of tissue, and integration time of time resolved measurements has been studied. We find that light absorption within the object already acts as a natural filter to suppress long pathlengths of strongly scattered photons. Compared to the case of no absorption, we observe a considerable improvement of the spatial resolution for realistic values of the absorption length and of the tissue thickness. We conclude that by time of flight methods, the spatial resolution in breast tissue with thickness of about 3 - 4 cm may be improved by at most a factor of two, once absorption is taken into account properly.