M. Teranishi

N. Iwama

S. Yamaguchi

Y. Nagayama

National Institute for Fusion Science (NIFS-Repository)

 Data Analysis Study for Microwave Tomography System Implementation Teranishi, M. (Dept. of ISM, Hiroshima Inst. Tech.) Iwama, N. (School of Informatics, Daido Univ.) Yamaguchi, S. (Dep. of Pure and Applied Phys., Kansai Univ.) Nagayama, Y.   The purpose of study is to develop the image reconstruction method for the microwave computerized tomography (microwave CT) with high space resolution. A new microwave imaging system is under development on the basis of the advanced measurement technology that has been built up for the microwave imaging reflectometry (MIR) of high temperature plasma. The system will serve purposes of practical imaging such as the breast cancer detection and the concrete pillar diagnostics. The system will be able to emit microwaves to objects with frequency variable and higher than those of the conventional practical imaging systems, and receive the scattered waves with phase information. After assemblage of the fundamental measurement components (a transmitter and a receiver antenna array, a data acquisition system) of our microwave imaging system, a function of measuring scattered microwave was tested for a dielectric cylindrical phantom (Fig. 1). By sweeping the microwave frequency in the range from 8.0 to 9.4 GHz, scattered microwaves were received in the form of complex signal by a quadrature detection circuit at 4 channels out of 16 channels of the receiver antenna array (Fig. 2). From the aspect of data analysis study, furthermore, recent works of microwave imaging such as the distorted Born iterative method (DBIM)1), a frequency-domain inversion with 3D series expansion2) and the time-domain inversion3) were reviewed to frame our concept towards good methods of image reconstruction. When an object is illuminated in the two-dimensional scheme by a TM incident wave ei(r) with time dependence of exp(-iωt), the electric fields e(r) in the object and e(s) at a receiver are expressed as � � � (1) and .            (2) Here, c(r) and G(r, r’) denote the contrast function of complex permittivity and the Green function, respectively, and k0 is the wavenumber in free space. When e(s) is observed at several points in a multi-transmitter configuration, determining c(r) from the acquired data is a nonlinear problem of image reconstruction. After pixellating the object region, the problem can be written in an algebraic equation A(c)c = es     (3) in order to determine the unknown image vector c from the data vector es of the whole receiving system. The coefficient matrix A(c) is calculated depend on the solution vector c, the inversion of Eq. (3) has strong ill-posedness. The DBIM solves this nonlinear inversion problem iteratively by solving linear approximate equations, whose coefficients are modified by forward calculation of the scattered field with the finite difference time domain (FDTD) analysis. This DBIM with FDTD is equivalent to the least square minimizing method that solves this nonlinear problem directly by using a Newton type minimizing technique4). Due to massive computational cost of FDTD, hardware accelerators are used to reduce the imaging time to a reasonable level. Effective reduction is obtained moreover by introducing an orthogonal series expansion on the inside of object with a matrix decomposition technique2). The geometrical knowledge of object boundary leads to a notable image improvement also in the time domain inversion3) that is based on fitting to the waveforms of pulsed scattering signals and properly involves the multi-frequency stabilizing effect. The possibility of reducing the computing time with higher resolution was investigated on the usage of new methods of matrix decomposition and of solving ill-conditioned linear equations of large size. The preparation of microwave imaging experiment was well progressed.  1) W.C. Chew and Y.M. Wang: IEEE Trans. Medical Imag., MI-9 (1990) 218. 2) D.W. Winters, J.D. Shea, P. Kosmas, B.D. Van Veen, and S.C. Hagness: IEEE Trans. Medical Imag., MI-28 (2009) 969. 3) J.E. Johnson, T. Takenaka et al.: IEEE Trans. Biomed. Eng., BE-55 (2008) 1941; BE-56 (2009) 2232. 4) A. Franchois and C. Pichot: IEEE Trans. Antennas Propagat., AP-45 (1997) 203. Fig. 1  Experimental setup of microwave measurement test. Fig. 2  Result of frequency sweeping test. 448§27. ata Analysis Study for Microwave Tomography System ImplementationTeranishi, M. (Dept. of ISM, Hiroshima Inst. Tech.),  Iwama, N. (School of Informatics, Daido Univ.),  Yamaguchi, S. (Dep. of Pure and Applied Phys., Kansai Univ.),  Nagayama, Y.

Data Analysis Study for Microwave Tomography System Implementation

Abstract

Similar works

Full text

Available Versions

National Institute for Fusion Science (NIFS-Repository)