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Effects of the background optical properties on time-resolved transmittance imaging

The effects of the background optical properties on the performance of imaging of realistic absorption and scattering inhomogeneities in diffusive media were studied experimentally by varying the optical coefficients of both background and inhomogeneity, while keeping constant the optical contrast between the two media. Images were constructed from a matrix of time-resolved transmittance measurements performed with time-correlated single photon counting. Data were collected every 0.2 cm over a 6 cm X 6 cm area from realistic tissue phantoms containing cylindrical inhomogeneities (1 cm height and 1 cm diameter) embedded in a 5 cm thick turbid slab. The optical coefficients of the background were varied in the ranges of 5 - 15 cm-1 for the transport scattering and 0.02 - 0.08 cm-1 for the absorption. The optical contrast for the inclusions was kept at values between -50% and +50% for the scattering and between -75% and +300% for the absorption. The data show that a strongly scattering and/or absorbing background can improve the detection capability of time-resolved imaging. From these results, advantage can be taken for a proper choice of the illumination wavelength to be used in transmittance imaging for diagnostic purposes.