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

Doctoral thesis, 2013

This thesis focuses 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, 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 big 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. With the development of solid state technology, time domain measurement technology has become more and more attractive for ultra-wideband applications. This is due to the low cost, high speed and simple structure. The accuracy of time domain systems is the main concern for the use in medical applications. In the first part of the thesis, we studied the accuracy issue of time domain systems. Theoretical analysis was performed to estimate the measurement accuracy and the results were 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, with comparable results in the permittivity reconstructions. The study of a high contrast breast model showed that when the amplitude uncertainty and phase uncertainty of measurements were less than 1.5 dB and 15 degrees, the effects of noise on reconstructed images were 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 demonstrated the capability of the developed system for imaging.