Abstract-This paper proposes a new method to display microwave images of breast tissue, based on estimation of local microwave velocity from time of flight 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 field 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-Difference Time-Domain simulations. The basis functions, used with a regularisation scheme to improve numerical stability, reduce the dimensionality of the inverse problem for computational efficiency and also to improve the robustness to error in velocity estimation. The results support previously published findings that the wavelet transform is suitable for robust measurement of time of flight even in clinically significant simulations, and shows that the velocity contrast images can be constructed so different 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.
Ultra-wideband radar imaging is a promising modality of imaging for breast cancer detection, based on the dielectric contrast between healthy and pathological tissues. Its aim is to create a map of microwave scattering, and has already proven encouraging results. Unfortunately, the tumor extraction procedure used for reconstruction of the scattering volume leads to the appearance of an artifact called twin target, where a single tumor is expected. In this paper, a signal processing technique is presented to remove this twin target and enhance the contrast of the final image. The radar system and image formation algorithm are first described to explain the origin of the twin target. Experimental data are then acquired and processed by our correction algorithm, demonstrating its ability to fix the twin target issue.Index Terms-Microwaves, radar imaging, breast cancer detection, signal and image processing.
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