| When the physiological and pathological structure of biological tissue changed,electrical conductivity of tissue changed accordingly.Therefore,the early diagnosis of cancer can be provided by detecting the tissue conductivity to find the physiological and pathological conditions of the tissue structure in time.Magneto-acousto-electrical tomography(MAET)is a novel medical imaging method.Due to the use of ultrasonic excitation and electrodes of electrical impedance detection,its image has high resolution and high contrast of electrical impedance tomography.In the aspect of theoretical study,the wave equation of acoustic field in time domain and Helmholtz equation in frequency domain are established in this paper.The ionic conductivity model is established from the microscopic point of view.The equation for solving the positive problem of electromagnetic field in the practical process is derived.The expressions formula of one-dimensional magneto-acousto-electrical tomography signal and Wiener inverse filter formula are established.In the aspect of numerical simulation,finite element simulation software COMSOL Multiphysics is used to study the positive problem of acoustic field in time domain and frequency domain.According to the equation of positive problem of electromagnetic field in the practical process,the finite element modeling is carried out and the simulation results are consistent with the real experimental results.The theoretical correctness of MAET is verified.The simulated MAET data are used to develop the conductivity reconstruction algorithm.Later on,the conductivity distribution graph is obtained.In order to reconstruct the electrical conductivity images of irregular objects,a multi-angle scanning method is proposed.Finally,the reconstruction images close to the true conductivityIn the aspect of hardware platform,a set of experimental platforms based on digital oscilloscope acquisition are built.The electromagnetic interference of the instantaneous acquisition system excited by ultrasonic is verified.In order to restrain the electromagnetic interference,insulation oil and sound transmission box are used.Finally,good results have been achieved.On the basis of the above-mentioned platform,the 0.1 microvolt MAE signal is successfully detected and the one-dimensional conductivity distribution graphs of rectangular phantom and layered phantom are obtained by using inverse Wiener filter deconvolution.Thus,the validity of the algorithm is verified in the experiment.Using 2.5MHz ultrasound to excite the multi-boundary phantom,it is proved that the resolution can reach 1 mm.Subsequently,the electrical conductivity image of pork tissue was obtained.It is proved that the tissue in vitro was still feasible in MAET.Finally,it is verified that the linear array probe can obtain the same MAE signal as the single element probe,which lays a foundation for the future use of Verasonics to complete the integration of ultrasonic emission and MAE signal reception.Finally,this paper summarizes the work accomplished at this stage and presents future perspectives on ultrasonic linear array excitation,encoding MAET and mouse experiment. |
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