Figure 7.

(a) Heterogeneous signal processing of Tx: 6 and Rx: 26 (black circles) leads to irregularly shaped equipotential surfaces within the breast region. Outside the hemisphere where the antennas are located (dashed line), the relative permittivity is constant which produces an ellipsoidal shape there. (b) Quasi-homogeneous processing of the same signals using the average relative permittivity of the in-breast tissue projects the large signal amplitudes not at the location of the tumour so that its localization fails. This example illustrates the systematic error that occurs through the homogeneity assumption.