Weakly inhomogeneous media tomography.

Our objective is to develop an ultrasonic scanner for breast imaging. High resolution is obtained by using wide-band spherical waves transmitted and measured in the near field zone (i.e., close to the skin) all around the organ. The tomographic approach that we adopt allows us to use low central frequency waves (3-7 MHz) that are suitable for good penetration while maintaining high resolution and contrast. The procedure is thus suitable for early detection of tumors and increases the chances of total recovery. The novelty of the present reconstruction procedure is that it associates the signals acquired in transmission to the data measured in reflection over a large aperture. This enables us to correct the phase aberration induced by weak inhomogeneities whose sizes might be several wavelengths. Numerical tests based on Finite Difference Time Domain (FDTD) simulations demonstrate the greater fidelity of the reconstruction.