Application of Microwave Techniques in Breast Imaging

The detection of breast cancer at its early stage reduces the treatment cost and the mortality rate. Microwave imaging techniques have been proposed to complement the existing X-ray mammography to screen women. They exploit the dielectric contrast between malignant and healthy tissue in the microwave range.;The second subject of this thesis is to use a commercial software, SEMCAD, to construct numerical breast models. We use the classification and regression tree analysis to approximate the heterogeneous tissue region, which averages out the noise inherited in the magnetic resonance images and reduces the number of solids to fill the tissue region. These breast models can be combined with complex antennas for full-wave electromagnetic simulations.;A numerical evaluation of the microwave radar and microwave-induced thermoacoustic imaging technique is presented. We find that the contrast in radar signals is due to permittivity and conductivity, while the contrast in thermoacoustic signals is due to conductivityheat capacity ratio. Due to the wave physics and the fact that human breast is electrically heterogeneous but acoustically homogeneous, images acquired from the thermoacoustic signals exhibit better quality than the images from the radar signals.;Finally, we show that the antennas in microwave tomographic systems are for transmitting and receiving microwave signals, and the antennas in microwave-induced thermoacoustic systems are for heating. It is not feasible to construct a single system with antennas that simultaneously meet the requirements of these two systems.;The first subject of this thesis is to solve the problem of a plane wave scattered by a multi-layer sphere. From this model and the recent measurements of the dielectric properties of the breast tissue, we predict the strength of this response as the tumors are buried in different tissues. These results identify the requirements on the microwave radar systems for breast tumor detection.