Investigation On The Methodologies Of Near-field Microwave Echo Imaging

Microwave near-field imaging of breast cancer relies on the significant difference of the dielectric constants of cancerous tissue and normal tissue at microwave frequecies. The contrast means that the tumor scatters the irradiating electromagnetic waves considerably. The characteristics of detecting targets can be determined by analyzing of the characteristics of backscatter. Through the conjoint analyzing of the data from multiple probing points, the distribution of the dielectric constants is obtained and imaged by inversing calculation. The technology has good prospects of an adjunct to good health survey for the advantages of small detection power of microwave (mW level) in the backdrop of high incidence of breast disease.The nonlinear relationship of microwave backscattering and the dielectric constants of breast tissues are caused by the complex scattering properties of microwave through inhomogeneous medium. So the issues, which are relative to the qualitative characteristics by backscattering from tissue, become extremely complex. Firstly, we establish the media model, which is similar to living breast tissue, from the studies on the electromagnetic properties of the breast tissues. And the microwave propagation in breast tissue is analyzed on this model. Secondly, the transmission mechanism of the microwave in breast is assessed by the electromagnetic theory, and the transport relationship of the valuation between upper limits and lower limits is obtained. Thirdly, the former results are validating by experiments. Finally, the data processing methods, which are suited for the near-field environments, are obtained from mechanism of the microwave transmission in breast. And these methods provide advanced supports on theoretical and experimental for further studies.In this paper, media model of a breast is the basic of the discussion. And organization the paper from four parts:(1) media model of a breast; (2) the model-data acquisition from backscattering wave; (3) computed imaging techniques of conjoint multiple data and (4) the platform of model-data process and computation, and we make a detailed discussion of each parts. The main contents of this paper are:Firstly, this paper proposed a breast medium model, which is fit for practical calculating the real breast, with the characteristics of living breast organization, based on the former research. Then this paper discussed the process of calculation and verification on this breast medium model, and also found a suitable method to handle the data of practical computing environment. In the discussion, this paper studied the electromagnetic characteristics of inhomogeneous medium, deduced the relationship of electromagnetic function using the nonmagnetic characteristics of breast tissues. Finally, this paper gave the evaluation of upper and lower limit for the interaction relationship between the near field tissue and he electromagnetic. Meanwhile, this paper verified that if the theory is corresponding to practice of the above model, with the experiment.Secondly, we research the mechanism of the microwave excitation and data acquisition when the microwave irradiates into living breast. Especially, we discuss the method of data acquisition from single detecting point. The quarter iteration of FRFT algorithm is proposed, which is appropriate to the process of this kind of signal for the characteristic of the realsignals. Then, a processing technique of auxiliary signal is presented by using the state of the system itself. Moreover, we design several appropriate experiments to verify the effect of the extracted data. At the end of this chapter, we propose the compensation of microwave transmission in the breast internal under the near-field condition. The multiple data joint calculation is based on the compensation.Thirdly, this paper analyzes and calculates the multiple sampling data based on the data sampling from single point. The space model is obtained according with the train of thought:from simpleness to complexity, from the linear computation to nonlinear computation. This paper gives several possible calculation models for analysis and discusses the simulation results of the corresponding models.Fourthly, we synthetically analyze the calculation processes of real data on the basis of multiple points'model. The experiment of "a metal blade in boneless pork" is designed combining the request of the real sampling. We certify that the system parameters by calculating agree with the parameters of real system, and contrast the parameters of the known target space and the parameters by calculating. Then we analyze the reason of the errors. At last, we optimize the real sampling process, and give a process flow from acquisition data on signal point to imaging. That can provide a reliable platform of theory and experiment for the real data processing.Fifthly, we develop software for this system on the basis of the data processing on multiple points. The fifty real patient cases, supplied by collaborating institution, were run in this software. In this software, this chapter researches the flow of the processing of sampling data, the suspicious targets marked in image. And the discussion topics are the key techniques of the software such as the extraction of lower limit in inverse calculation.Finally, we made a brief summary of the current issues and the future direction of this technology. In this paper, we present a new medical imaging method for the early detection of breast cancer in microwave near-field.