MICROWAVE CONTRAST IMAGING OF BREAST TISSUE FROM LOCAL VELOCITY ESTIMATION

This paper proposes a new method to display microwave images of breast tissue, based on estimation of local microwave velocity from time of ∞ight measurements. Its computational demands are low compared with tomography. It has two major components: 1) the estimation of the travel time of microwaves across the tissue between a set of antennae using a wavelet decomposition, and 2) the estimation of the microwave velocity fleld from the set of travel times using a low dimensional set of radial basis functions to model local velocity. The technique is evaluated in 2-D on clinical MR-based numerical breast phantoms incorporated in Finite-Difierence Time-Domain simulations. The basis functions, used with a regularisation scheme to improve numerical stability, reduce the dimensionality of the inverse problem for computational e-ciency and also to improve the robustness to error in velocity estimation. The results support previously published flndings that the wavelet transform is suitable for robust measurement of time of ∞ight even in clinically signiflcant simulations, and shows that the velocity contrast images can be constructed so difierent regions of breast tissue type can be distinguished. In particular, the presence of a tumour is clearly detected, demonstrating the potential of this approach for breast screening. Keywords: Biomedical signal processing; Microwave imaging; Image reconstruction.