An Ultrawideband Microwave Imaging System for Early Detection of Breast Cancer

Motivated by the critical need for complementary and/or alternative modalities to X-ray mammography for early stage breast cancer detection, we have proposed a method of ultrawideband microwave imaging for detecting backscattered energy from small malignant breast tumors. This thesis presents a detailed numerical and experimental investigation of the proposed microwave imaging system. In the proposed system configuration, each antenna in the array sequentially transmits a low-power UWB signal into the breast and records the backscatter. The backscatter signals are passed through a beamformer, which spatially focuses the waveforms to image backscattered energy as a function of location in the breast. First a simple beamforming method using basic time-shift-and-sum beamforming algorithm is proposed. Our 2-D and 3-D numerical studies have demonstrated the feasibility of detecting backscattered energy from small malignant breast tumors using this straightforward scheme without solving the inverse problem. Improved algorithms for both removing artifact components and space-time beamforming are introduced later. The robustness of these algorithms is investigated using extensive numerical studies. The preliminary experimental investigation of the microwave imaging system is based on multilayer simple breast phantom consisting of a homogeneous normal ii breast tissue simulant covered by a thin layer of skin simulant. A small synthetic malignant tumor is embedded in the breast phantom. We have developed several tumor simulants that yield the range of dielectric contrasts between normal and malignant tissue that are expected in clinical scenarios. A microwave sensor comprised of a planar synthetic array of compact ultrawideband (1-11 GHz) antennas is used to transmit and receive microwave energy. Small (< 5-mm) synthetic tumors with malignant-to-normal dielectric contrasts down to 1.5:1 are successfully imaged. Our experimental results suggest that microwave imaging via space-time beamforming offers the potential of detecting small breast tumors using state-of-the-art but readily available hardware and robust signal processing algorithms. I certify that I have read this thesis and certify that in my opinion it is fully adequate, in scope and in quality, as a dissertation for the degree of Doctor of Philosophy. iii In the memory of my father. iv Acknowledgements I would like to extend my deepest appreciation and gratitude to the faculty at University of Wisconsin − Madison. In particular, I want to thank my advisor Susan C. Hagness, for her guidance not only on my research project, but throughout my graduate program. She has been an extraordinary advisor, mentor, and role model to me. I also want …