Nowadays x-ray mammograms are used as the main technique in breast cancer detection. However, this technique introduces some problems such as ionising radiation, breast compression and difficulty in imaging women with dense breasts. These limitations of x-ray mammography provide clear motivation for the development of a complementary breast-imaging tool to assist in detection and diagnosis. Mammography may also produce false negatives. Estimates of the numbers of cancers missed by mammography are usually around 10%-30%. This means that of the 350 per 100,000 women who have breast cancer, about 35-105 will not be detected by mammography. Reasons for not seeing the cancer include observer error, but more frequently it is because the cancer is hidden by other dense tissue in the breast and even after retrospective review of the mammogram, it also can produce false positives. When the test shows a problem when none exists, the result is called a false positive. Microwave breast tumour detection is safer to patients because both ionising radiation and breast compression are avoided. Microwave breast tumour detection is less expensive than other methods such as magnetic resonance imaging. It also has the potential to be more sensitive and specific to detect small tumours. Microwave imaging is a promising technique for breast cancer detection. The reason for using microwaves is to exploit the difference between the electrical properties of normal tissue and malignant tissue in the ultra-wideband frequency range. So it is expected that microwave imaging can serve as an alternative or complementary method in breast cancer detection in future.
This thesis presents the study and design of a microwave imaging system using ultra-wideband technology for breast cancer detection. The context of this research covers a theoretical study, a design approach and implementations of the integrated designed imaging system. Some original contributions to the field of research are the development of realistic breast phantoms; the development of UWB tapered slot antennas and the design of integrated scanning system for laboratory assessment of the diagnostic tool for breast cancer detection.
Breast tissue heterogeneity has been neglected in many microwave-imaging studies that simplify the imaging process by using homogeneous breast phantoms. In this research the fabrication of heterogeneous breast phantoms to mimic the electromagnetic features of realistic female breast is described. The fabricated phantoms emulate the female breast tissue which is heterogeneous in nature and include mainly fat and fibro glandular. In addition to that, objects that emulate breast tumour are fabricated and tested. The contrast between malignant and glandular tissues in the fabricated phantoms is made as low as 10% both in permittivity and conductivity. This low contrast representation is important to explore the potential of the designed microwave imaging system as most breast tumours appear within the fibro glandular tissues.
The development of a microwave imaging system requires an ultra-wideband antenna that should be small in size have a directive radiation pattern and support distortion-less transmission of short duration pulses. In this thesis, a compact tapered slot antenna is designed to meet these features. It is used in the designed system for experimental assessment of breast cancer detection.
The test bed for the automated scanning platform is developed. Using the designed scanning system, a high resolution hemispherical scan can be achieved by rotating the imaged object placed on a suitable turntable. This thesis also discusses the laboratory assessment of the quality of two-dimensional images taken for the fabricated phantoms. Some imaging results using background effect removal technique for both homogenous and heterogeneous breast phantoms are presented. A special calibration technique is used to compensate for the antennas internal reflections. A comprehensive simulation study on the electromagnetic waveforms inside the target area is performed using the full-wave electromagnetic solver-Computer Simulation Technologies (CST) Microwave StudioTM. Time domain and frequency domain image reconstruction algorithms are developed and tested on single and multiple targets. If the medium for the signal propagation inside the target is dispersive, an image reconstruction algorithm relying on the direct use of the frequency-domain data is shown to be advantageous. A suitable window to minimise the adverse effects of finite bandwidth data is also applied. It is found that the designed system as a whole is able to detect small tumours even in a high-density breast with a dielectric contrast as low as 1:1.3. The use of the system for the detection of two tumours in a dense breast is also successful as revealed in the experimental results. The operation of the system is verified to confirm the absence of any false-positive alarms. Lastly, to quantify the success of the imaging system, the metrics parameters are calculated for the imaging results.