Xuezhi Zeng

Experimental Investigation of the Accuracy of an Ultrawideband Time-Domain Microwave-Tomographic System

The measurement accuracy of an ultrawideband (UWB) time-domain microwave-tomographic system is investigated. In order to make an assessment of the random variation of the measurements, the measurement repeatability of the system is evaluated by comparison with an UWB frequency-domain system. A phantom is imaged with the time-domain microwave-tomographic system, and the reconstructed images are compared with those obtained by using the frequency-domain system. The results suggest that with the averaging tens of measurements, the time-domain system can achieve the same level of measurement repeatability as that of the frequency-domain system in the interesting frequency range of microwave tomography. The imaging results, however, indicate that the phantom reconstruction does not require such high measurement accuracy. The permittivity profile of the phantom reconstructed from the nonaveraging time-domain measurements is very similar with that obtained by means of the frequency-domain system.

Accuracy Evaluation of Ultrawideband Time Domain Systems for Microwave Imaging

We perform a theoretical analysis of the measurement accuracy of ultrawideband time domain systems. The theory is tested on a specific ultrawideband system and the analytical estimates of measurement uncertainty are in good agreements with those obtained by means of simulations. The influence of the antennas and propagation effects on the measurement accuracy of time domain near field microwave imaging systems is discussed. As an interesting application, the required measurement accuracy for a breast cancer detection system is estimated by studying the effect of noise on the image reconstructions. The results suggest that the effects of measurement errors on the reconstructed images are small when the amplitude uncertainty and phase uncertainty of measured data are less than 1.5 dB and 15 degrees, respectively.

Development of a Time Domain Microwave System for Medical Diagnostics

In this paper, a time-domain system dedicated to medical diagnostics has been designed, a prototype has been built and its performance has been evaluated. Measurements show that the system has a 3-dB bandwith of about 3.5 GHz and a signal to noise ratio over 40 dB in the frequency range about 800 MHz to 3.8 GHz. The system has been used to perform a microwave tomographic image reconstruction test. The same target was reconstructed based on data measured with a network analyzer. A comparison between the images shows very small differences, and proves the functionality of the time domain system.

Effects of noise on tomographic breast imaging

We study the effect of noise on microwave breast imaging by numerical simulations. A high contrast breast model is considered and the image reconstructions are carried out in time domain using a nonlinear inversion algorithm. A relative reconstruction error is defined in order to quantitatively evaluate the image distortion due to noise. The relative reconstruction errors of noisy reconstructions are obtained when different levels of amplitude and phase errors are taken into account.

Accuracy evaluation of time domain measurement systems for microwave tomography

The measurement accuracy of time domain systems for microwave tomography are evaluated through system level simulations and compared with that of a network analyzer based frequency domain system. In the analysis, both a time domain ultra-wideband (UWB) impulse and multiband system architectures are considered. It is shown that the measurement error of the time domain systems mainly comes from analog to digital (A/D) conversion. For a simple comparison case, the relative measurement error involved in an estimated object response signal from the time domain UWB impulse system and UWB multiband system measurements are around three times and ten times higher than that from frequency domain system.

Design and Performance Evaluation of a Time Domain Microwave Imaging System

We design a time domain microwave system dedicated to medical imaging. The measurement accuracy of the system, that is, signal-to-noise ratio, due to voltage noise and timing noise, is evaluated. Particularly, the effect of coupling media on the measurement accuracy is investigated both numerically and experimentally. The results suggest that the use of suitable coupling media betters the measurement accuracy in the frequency range of interest. A signal-to-noise ratio higher than 30 dB is achievable in the range of 500 MHz to 3 GHz when the effective sampling rate is 50 Gsa/s. It is also indicated that the effect of the timing jitter on the strongest received signal is comparable to that of the voltage noise.

A computational study using time reversal focusing for hyperthermia treatment planning

In hyperthermia treatment planning (HTP) the goal is to find the amplitudes and phases of antennas in the applicator to efficiently heat the tumor. To do this prior information regarding tumor characteristics such as the size, position and geometry, in addition to an exact model of the hyperthermia applicator is needed. Based on this information, the optimal frequency of operation can be determined. In this paper the optimum frequency for hyperthermia treatment based on the tumor and applicator characteristics, using time reversal as the focusing technique, is studied. As prior information, we consider tumor size and position, the number of the antennas in the applicator and the frequency characteristics. The obtained optimal frequency range is found using hyperthermia quality indicator values calculated from simulations. We also determine the optimum position of the virtual source in the initial step of the time reversal method to increase the quality of the treatment.

Noise performance comparison between two different types of time-domain systems for microwave detection

This paper compares the noise performance of two different types of time-domain microwave detection systems: a pulsed system and a pseudo-random noise sequence system. System-level simulations and laboratory-based measurements are carried out in the study. Results show that the effect of timing jitter is more significant on the measurement accuracy of the pseudo-random noise sequence system than that of the pulsed system. Although the signal power density of the pseudo-random sequence system is tens of dBs higher than that of the pulsed system over the frequency band of interest, the signal-to-noise ratio difference between these two systems can be just a few dBs or even smaller depending on the jitter level.

Microwave based diagnostics and treatment in practice

Globally, around 15 million people each year suffer a stroke. Only a small fraction of stroke patients who could benefit from thrombolytic treatment reach diagnosis and treatment in time. To increase this low figure we have developed microwave technology aiming to differentiate hemorrhagic from ischemic stroke patients. The standard method for breast cancer diagnosis today is X-ray mammography. Despite its recognized ability to detect tumors it suffers from some limitations. Neither the false positive nor the false negative detection rates are negligible. An interesting alternative being researched extensively today is microwave tomography. In our current strive to develop a clinical prototype we have found that the most suitable design consists of an antenna array placed in a full 3D pattern. During the last decade clinical studies have demonstrated the ability of microwave hyperthermia to dramatically enhance cancer patient survival. The fundamental challenge is to adequately heat deep-seated tumors while preventing surrounding healthy tissue from undesired heating and damage. We are specifically addressing the challenge to deliver power levels with spatial control, patient treatment planning, and noninvasive temperature measurements.

Microwave technology in medical diagnostics and treatment

There is a great need for novel diagnostics and treatment tools in todays healthcare. In this paper we describe our development and progress in novel microwave based diagnostics and treatment applications. The target applications are stroke diagnostics, breast cancer detection and microwave hyperthermia.