| One of the fastest growing fields of technology-a field of astounding recent achievements and even more ambitious hopes-is biomedical engineering. Medical imaging, one of the research branches in biomedical engineering, plays an important role in improving medical diagnosis and treatment.Measurements indicate that the relative dielectric constant and conductivity of high-water-content tissues are about an order of magnitude greater than those of low-water-content tissues. Moreover, the dielectric constant and conductivity of tumors are quite different from those of normal tissues, which makes the tumor detection possible by using electromagnetic means.Microwave imaging (MI) and electrical impedance tomography (BIT) have been developed for many years. However, their resolutions are limited and not suitable to determine the electric properties of thin tissues, such as skin. Moreover, the techniques of MI and BIT are much complicated, and the equipments are either complex or expensive.A 3-dimensional (3D) reconstruction method of electric properties of superficial tissues by noninvasive measurement of human body is presented in this paper. By this reconstruction method, the dielectric constant and conductivity of each tissue in multi-layered superficial structure, especially of very thin tissues, such as skin, can be obtained.In the reconstruction based on a stratified uniform tissues model, a patch-antenna probe excited by coaxial line is designed and optimized by MGA (Micro Genetic Algorithm) combined with FDTD (Finite Difference Time Domain). Near fields established by the optimized probe are concentrated in a small region and able to penetrate into deeper layers of the tissues. Thus, the complex superficial tissues can be described by a multi-layered-uniform tissues model.The reconstruction of dielectric constant and conductivity of tissues at each layer is a nonlinear and ill-posed problem. Both GA and MGA methods are used to solve the inverse problem. Simulation results indicate that not only the dielectric constant and conductivity of each tissue can be reconstructed, but also the thickness of first two layers can be achieved.The appropriate population size of GA is about 100 for this problem. Some techniques, such as niching technology based on sharing scheme, tournament selection with elitism, and uniform crossover, are used to improve the performance of GA and MGA.The influences of measurement data on reconstruction results are investigated in this paper. The reconstruction results are no longer reliable when the measurement error is larger than 10%. The appropriate number of measurement data should be between 20 and 50 when the number of unknown parameters is 14 in this problem. Simulated results are also in agreements with experimental results, which shows the validity of this reconstruction method.There always exist some blood vessels in superficial tissues. Sometimes these blood vessels are large and cannot be ignored in modeling. Therefore, the impacts of blood vessels and flowing blood on the reflection coefficient are studied. Simulation results show that: a) The blood vessels in layered tissues may have a great influence on the reflection coefficient. The influence on reflection coefficient depends much on frequency, which will also definitely affect the reconstruction of the electric properties of tissues, b) The change of reflection coefficient resulted from the variation of diameter and position of blood vessel is not dramatic, c) The change of reflection resulted from the flowing blood can hardly be noticed.The dielectric constants and conductivities of skin, fat and muscle, as well as thickness of the skin and fat on the back of a human body are reconstructed using the above method. The reconstructed thicknesses of skin and fat are in good agreements with the specimen, and the electric properties of tissues are in agreement with the literature results. Both experimental results and reconstructed results show that the distribution of electric properties o...
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