Imaging of absorbing inhomogeneities within highly diffusing media

A comparison among different techniques used for breast imaging has been carried out by using a Monte Carlo (MC) code to simulate confocal scanning on a diffusing slab containing absorbing inhomogeneities. The MC code evaluated the temporal point spread function (TPSF) for many positions of the source- receiver system with respect to the inhomogeneity. Each TPSF was fitted using the diffusion equation solution for a homogeneous slab. The information contained in each TPSF was summarized in three parameters: the absorption coefficient, the reduced scattering coefficient and the amplitude factor. An image was obtained plotting each of these parameters. To simulate the time gating technique the analytical functions obtained from the fit were used to evaluate the energy received within short gating times. To simulate the frequency domain technique the Fourier transform of the analytical function was calculated. The results obtained from simulations showed that a good estimation of the dimension of an absorbing inhomogeneity can be retrieved from the images obtained either from continuous wave domain, or time domain, or frequency domain measurements. The better contrast and the independence of the image quality on absorption properties of the diffusing medium indicates that the time gating technique is the one producing the best image quality.