1 Electromagnetic Systems, Department of Electrical Engineering, Technical University of Denmark2 Department of Electrical Engineering, Technical University of Denmark3 ElectroScience, Department of Electrical Engineering, Technical University of Denmark4 Center for Hyperpolarization in Magnetic Resonance, Center, Technical University of Denmark
Among the various alternative breast imaging modalities to improve breast cancer detection, microwave imaging is attractive due to the high dielectric property contrast between the cancerous and normal tissue and has received a significant interest over the last decade. This thesis presents the research and development of a microwave imaging system capable of reconstructing the dielectric properties of the female breast. As part of this study, a brief review of the ongoing research in the field of microwave imaging of biological tissues is given, with major focus on the breast tumor detection application. The current microwave imaging systems are classified on the basis of the employed measurement concepts. Within the various microwave imaging techniques under development, the active frequency domain method is found to be one of the most promising and is chosen as a basis for the development of the imaging instrument. The active frequency domain method allows for a wide dynamic range, which is important for image quality. It is based on the measurement of the complex transmission coefficient in several directions through the imaging domain containing the object to be imaged (the breast). This data is then used to reconstruct an image, which consists of a spatial distribution of the complex permittivity in the imaging domain. Using this image the cancer tissue can be detected due to its dielectric property contrast compared to normal tissue. The instrument employs a multichannel high sensitive superheterodyne architecture, enabling parallel coherent measurements. In this way, mechanical scanning, which is commonly used in measurements of an electromagnetic field distribution, is avoided. The system presented is the first reported 3D microwave breast imaging camera with parallel signal detection. The hardware operates in the frequency range 0.3 – 3 GHz. The noise floor is below -140 dBm over the bandwidth of the system. The dynamic range depends on the available incident power range and is limited by the channel to channel isolation of 140 dB. The work presented in this thesis encompasses a wide range of aspects related to hardware design including a system architecture and custom components development. Several novel compact microwave components, such as planar bandpass filters and wideband impedance transformers, are proposed. A monolithically integrated system on a chip for the imaging system front-end is designed, which allows to further improve the imaging system performance and reduces the cost of such class of instruments. The integrated circuit has been realised in a GaAs 0.18 μm pHEMT process and provides the main functions of a front-end, such as multiplexing, amplification, and mixing, in a frequency range of 0.1 – 8 GHz.