Microwave imaging for ultra-wideband antenna based cancer detection
Breast cancer is one of the most widespread types of cancer in the world. The key factor in treatment is to reliably diagnose the cancer in the early stages. Moreover, currently used clinical diagnostic methods, such as X-ray, ultra-sound and MRI, are limited by cost and reliability issues. These limitations have motivated researchers to develop a more effective, low-cost diagnostic method and involving lower ionization for cancer detection. In this thesis, radar based microwave imaging is proposed as a method for early breast cancer detection. This imaging system has advantages such as low cost, being non- invasive and easy to use, with high image resolution and its thus good potential for early cancer detection. In the first stage, an ultra-wideband Vivaldi antenna and a slot Vivaldi antenna are proposed, simulated and fabricated for breast cancer detection. The designed antennas exhibit an ultra-wideband working frequency. The radiation patterns also achieve the desired directional radiation patterns. The second stage of this study presents a planar breast phantom and a hemisphere breast phantom. These two breast phantoms are simulated and fabricated using CST microwave studio and tissue-mimicking materials respectively. Mono-static radar systems based on a single antenna configuration and an antenna pair configuration are then proposed. These two systems are used to measure the planar breast phantom and hemi- sphere breast phantom, with the scattering signals measured in the frequency and time domains. Based on the measurement results, it is concluded that the reflected energy increases when the antenna moves close to the tumour; otherwise, the reflected energy is reduced when the antenna moves away from the tumour. The received time domain scattering signals are processed first and then used to create microwave images to indicate tumour position. A clutter removal method is proposed to extract the tumour response from the received signals. The microwave images are then created using the tumour response based on the simulation and experimental results. The imaging results indicate that a 5 mm radius tumour can be detected. The tumour burial depth is also studied. A multi bio- layer phantom which contains deep and shallow buried tumours is simulated and measured using the Vivaldi antenna. A spectrum analysis method is proposed to distinguish between different tumour depths. The results indicate that a difference in depth of 15 mm results in a mean change of 0.3 dB in the magnitude of the spectrum. Discrimination between benign and malignant tumours is also considered in this study. The singularity expansion method (SEM) for breast cancer is proposed to discriminate between benign and malignant tumours based on their morphology. Two cancerous breast phantoms are developed in CST. The benign tumour is a 5mm radius sphere and the malignant tumour is a spiny sphere with an average radius of 5mm. The use of the SEM leads to the successful discrimination of these two tumours. This method provides a solution to discriminate between benign and malignant tumours similar size when the resulting images cannot provide sufficient resolution. A preliminary study of brain cancer detection is also concluded. Research in this area has never been implemented. A cancerous brain model is designed and simulated in CST. The antenna pair configuration is then used to measure the cancerous brain, with the scattering signals measured. Microwave images for brain cancer detection are then created based on the measurement results. The tumour is correctly indicated in the resulting images.