Research On The Characteristics Of Sound Source And The Algorithm Of Image Reconstruction In Magneto Acoustic Tomography

Early detection of cancer has clinical significances for its accurate diagnosis and effective treatment. Using the property of electrical characteristics of biological tissue changing before the occurrence of its morphological change, magneto-acoustic tomography with magnetic induction(MAT-MI) recently showed its powerful capability to reconstruct the distribution of electrical conductivities of biology tissue by combining the good contrast of electrical impedance tomography with the good spatial resolution of sonography. As a new functional medical imaging method, MAT-MI with noninvasive advantage is expected to be applied in the early detection of clinical cancer.For the method of MAT-MI, the conductive object is located simultaneously in both a static magnetic field and an applied time-varying stimulating magnetic field. An eddy current is induced in the object by the time-varying magnetic field. Consequently, the eddy current in the static magnetic field generates Lorentz force that leads to vibrations of cell of the object, and further emission of corresponding sound waves. Moreover, these generated ultrasonic waves can be collected by transducers so as to reconstruct an accurately distribution of electrical conductivity of the object. Although ten of research groups have paid much attention to the related theory, numerical simulation, and reconstruction algorithm of the MAT-MI so far, lots of unknown facts are still on the way to a clinical imaging method.In this work, numerical modeling and simulations of the signal generation process of MAT-MI was studied firstly. More importantly, the directional characteristic of the induced sound source was discussed theoretically, and the ultrasonic signals were calculated numerically.Furthermore, studies of inverse problem of the MAT-MI were carried out. In this study, the moment method was proposed to calculate and simulate the amplitude of Lorenz force, which could solve well the singularity problem of the discontinued boundary. Compared with previous algorithms, the proposed imaging method with the moment method can determine distributions both of boundaries of the sound source and of the internal acoustic source. As thus, the obtained image resolution could be improved. In the reconstruction of electrical conductivity, a new method of electrical conductivity reconstruction was proposed based on the tangential directions component of the induced current. The proposed method take into account the conductivity change of charge accumulation influencing on the Coulomb electric field, which could be applied not only in a conductivity distribution uniform model, but in a conductivity large changing model.Finally, a two dimensional electrical conductivity model was modeled and simulated numerically. A good consistence between of the reconstructed conductivity with the proposed algorithms and the original conductivity distribution illustrated preliminarily the availability of the proposed imaging algorithm of MAT-MI in this work.In summary, our studies also would offer a new way to further explore the method of MAT-MI and determine the direction of the future research.