Time Domain Systems for Microwave Imaging: Accuracy Evaluations and Prototype Design

Abstract: This thesis works on microwave hardware development for medical applications. In this thesis, we have evaluated the accuracy of time domain systems for medical imaging, and a time domain system dedicated to medical imaging has been designed, developed and tested. As a potential imaging modality for biomedical applications, ultra wideband microwave medical imaging has attracted a lot of attention in recent years. Most of the ultra wideband microwave imaging systems reported so far are based on commercial instruments, which are only appropriate for experimental purpose due to the high cost and the massive size. In order to speed up clinical trials, it is highly desirable to have a custom designed system with low cost, small size, high speed and enough accuracy. As the development of solid state technology, time domain measurement technology has become more and more attractive for ultra-wideband applications due to the low cost, high speed and simple structure. We therefore investigated on developing a suitable time domain system for microwave medical imaging. The accuracy of time domain systems is the main concern for medical applications. In the first part of the thesis, we studied on the accuracy issue of time domain systems. Theoretical analysis was performed to estimate the measurement accuracy of time domain systems and the results are verified by simulations and experiments. An imaging study was performed in order to compare the image reconstructions obtained by using a time domain experimental system and an ultra wideband frequency domain system respectively, and the results suggest insignificant difference between the permittivity reconstructions. In addition, in order to estimate required accuracy for medical imaging, the effects of measurement error on the imaging quality of different contrast objects are investigated. It is suggest that higher accuracy is required for the imaging of objects with lower contrast. The study of a high contrast breast model shows that when the amplitude uncertainty and phase uncertainty of measurements are less than 1.5 dB and 15 degrees, the effects of noise on reconstructed images are small. Based on the investigations and current technology limitations, we proposed a time domain system design dedicated to microwave medical imaging. A prototype was developed and its measurement accuracy was evaluated. An imaging test was also performed with the prototype and the results were compared with those obtained using our experimental system. The imaging results validate the imaging functionality of the developed system.