Theoretical limits and safety considerations for magneto-acousto electrical tomography

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2017
Ghalichi, Elyar
In this study, the performance of Magneto-Acousto-Electrical Tomography (MAET) method is investigated quantitatively by considering interrelations between its sensitivity, resolution and conductivity contrast. An analytical solution for the forward problem of MAET is derived for two-dimensional (2D) concentric bodies by Separation of Variables Method. The electric potential and the acoustic pressure are separated to their angular and radial components. The series coefficients for these solutions are obtained by their respective boundary conditions. These analytical solutions are compared to the numerical solutions calculated by COMSOL Multiphysics. The relative errors between these two solutions for electric potential and acoustic pressure are obtained. In both cases, the average relative error is below one percent. The electric potential on the boundary is related to the acoustic boundary acceleration analytically. From this potential expression, a sensitivity expression is derived relating fractional change in conductivity contrast to fractional change in the measured electric potential. This expression is a function of resolution and conductivity contrast of the imaging system. It also depends on the acoustic wave number and the dimensions of the body. The pair-wise relation between these parameters are presented. The sensitivity behavior of MAET is compared with Electrical Impedance Tomography and the improvements for small inhomogeneities are presented. For eccentric bodies, a modified expression for the sensitivity is obtained by conformal mapping. For arbitrary periodic boundary excitations, the sensitivity expressions of harmonic cases are combined to obtain a unified sensitivity expression. Moreover, the tissue heating concerns arising in MAET imaging method is investigated numerically for a simplified 2D breast model. The steady state temperature distribution in the model is evaluated for an external source free case. The medium is excited with a 16 element linear phased array transducer at 1 MHz. The amplitude of acoustic excitation is set to the mechanical safety limit (1.7 MPa) at 1 MHz. The heating profiles due to acoustic absorption and resistive Lorentz current dissipation are demonstrated. The maximum temperature change is below 1 Kelvin and within the thermal safety limits.  

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Citation Formats
E. Ghalichi, “Theoretical limits and safety considerations for magneto-acousto electrical tomography,” M.S. - Master of Science, Middle East Technical University, 2017.