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Transillumination of breast phantoms using diffuse photon density waves

Photon Migration through diffusive media studied in the frequency-domain is characterized by Diffuse Photon Density Waves (DPDWs). Theoretically, DPDWs propagation is described using the diffraction theory based on the diffusion approximation to the transport equation. Experimentally, 100 MHz modulated DPDWs are generated with our home-made frequency-domain set-up. The actual accuracy of this set-up is 0.3% in amplitude and 0.15 degree(s) in phase. The diffuse media probed are (optical)-breast-like phantoms which contain 5 mm-diameter inhomogeneities with inhomogeneity/background absorption and scattering contrasts of 1.1, 1.5, 2.0 and 4.0 respectively. Experimental results are compared to simulations and time-domain experimental results. Differences between absorption and scattering effects in the frequency-domain are highlighted. Main problems induced by phantom boundaries are presented. Two methods which aim to minimize lateral boundary effects are proposed and tested: the extrapolated lateral-boundary method and the direct polynomial or exponential fitting procedure. With these corrections, we are able to resolve well the two most contrasted inhomogeneities.