| Magnetoacoustic Tomography with Magnetic Induction(MAT-MI) is a new proposed imaging modality to image the electrical impedance of biological tissue, which combines the electrical impedance tomography with high contrast and sonography with high spatial resolution. Current researches on MAT-MI mainly concentrate on isotropic media which ignore the characteristics of conductivity anisotropy. However, some of the biological tissues, such as muscle and white matter in the brain, show significant conductivity anisotropy. Furthermore, compared with normal tissue, tumor tissue may have different conductivity anisotropic tensor. In MAT-MI, conductivity anisotropy has effect on the total amount and distribution of eddy current. Consequently, the influence on eddy current causes variation of acoustic source and acoustic pressure. If the characteristics of conductivity anisotropy are ignored, it will produce error in conductivity reconstruction when solving inverse problem of MAT-MI. Therefore, research on conductivity anisotropy media based on forward problem of MAT-MI has scientific significance for MAT-MI technology.In this thesis, the conductivity isotropic concentric and eccentric spherical models mimiking the gland tumors are established firstly. And forward problem is solved with the finite element method. The simulation results show that eddy current density varies in different region of conductivity. The location and boundary of imaging target are marked by acoustic source distribution clearly. The peak amplitudes of acoustic pressure at the sensor location are changed with the acoustic source on the boundary. The convergence of simulation results are also be evaluated in the eccentric spherical model. After setting the conductivity tensor to be anisotropic, the conductivity anisotropy models mimiking mammary gland tumor with different radius, conductivity and position are established. Compared the anisotropy simulation results with the isotropy ones, the results show that eddy current density variation can be seen on the direction where conductivity tensor changes. And the acoustic source distribution in anisotropy models becomes more complicated. The peak amplitudes of acoustic pressure at the detection position are varied significantly in the anisotropy models. This thesis provides theoretical fundamental for MAT-MI hardware experiment and image reconstruction. In order to solve the inverse problem more accurately and reconstruct high resolution image of conductivity, the influence of conductivity anisotropy in solving the problem of MAT-MI should be consider fully. |
