Simulating The Forward Problem Of Magnetoacoustic Tomography With Magnetic Induction (MAT-MI) And Experiment Study

In medical imaging,tissue electrical properties such as conductivity, permeability and the electromagnetic absorption coefficient as well as other nonlinear parameter are of interest in various applications of tissue electrical properties tomography. Reconstruction of these physical parameters may provide supplementary or even more useful information about the physiological and pathological status of biological tissue,and could be used to help early diagnosis.In traditional EIT,shielding effect and ill-posed inverse problem cause big problem for reconstruction the tissue impedance, and resolution is strongly depth-dependent since the sensitivity of the measured quantities to material disturbances rapidly decays with increasing distance from the measurement electrodes.Ill-posedness of the inverse problem that has to be solved to calculate images from the boundary measurements.An interesting attempt to increase the information content of the boundary measurements is based on the exploitation of interactions between different physical effects.Magnetoacoustic tomography with magnetic induction(MAT-MI) was proposed to achieve high spatial resolution noninvasive electrical impedance imaging by integrating magnetic induction and ultrasonic measurements. I In MAT-MI reconstruction of an acoustic source field can provide information not only acoustic properties but also tissue electrical properties. In MAT-MI,the object is placed in a static magnetic field and a time-varying magnetic field.The time-varying magnetic field induces eddy current in the object volume.Following that,the eddy current in the static magnetic field caused vibrations due to the Lorentz force and emits ultrasound waves.These ultrasound waves are collected by transducers surrounding the object and the reconstruction of the conductivity properties is obtained with a spatial resolution close to that of sonography.This dissertation provides a finite element method for solve the forward problem in magnetoacoustic tomography with magnetic induction(MAT-MI).Having obtained the magnetic flux distribution for the applied current in coil via use Ampere law, also the induced eddy current and pressure in object can be calculated in a two-layer sphere model with uniform conductivity distribution at each layer,and hence it can be determined electromagnetic field and pressure field for arbitrary shape or material properties can be solved using finite element method. The proposed method is verified by numerical simulation experiments. A experiment system for MAT-MI has been set up,implement a driving source for MAT-MI, we measure the pulse magnetic field of detection area. The measurement result was consentient with the numerical simulation experiment result.In this work,the contribution of the displacement curren is assumed to be much small that can be neglected,and assume acoustic homogeneity,in our simulation the acoustic speed is set to be a constant value.