According to the coupling relationship of electromagnetic field and acoustic field when electromagnetic field irradiates low conductivity objects, we carried out a study on the magnetoacoustic effect and thermoacoustic effect in pulsed magnetic excitation. In this paper, we provide the pressure wave equation in pulsed magnetic excitation based on the theory of electromagnetic field and acoustic wave propagation. A 2-dimensional coil carrying current and a circular thin sheet model were constructed to simulate the physical imaging environment. The transient electromagnetic field was simulated using finite element method. Numerical studies were conducted to simulate the pressures excited by magnetoacoustic effect and thermoacoustic effect according to the result of electromagnetic simulation. It was shown that the thermoacoustic effect played a leading role in the low conductivity objects on the microsecond Gauss pulsed magnetic excitation, and thermoacoustic effect and magnetoacoustic effect coexisted on the microsecond Gauss pulsed magnetic field and 0.2 T static magnetic field excitation. This study lays the foundation for the further application of magnetoacoustic tomography with magnetic induction and magnetically mediated thermoacoustic imaging.
As drug carriers, magnetic nanoparticles can specifically bind to tumors and have the potential for targeted therapy. It is of great significance to explore non-invasive imaging methods that can detect the distribution of magnetic nanoparticles. Based on the mechanism that magnetic nanoparticles can generate ultrasonic waves through the pulsed magnetic field excitation, the sound pressure wave equation containing the concentration information of magnetic nanoparticles was derived. Using the finite element method and the analytical solution, the consistent transient pulsed magnetic field was obtained. A three-dimensional simulation model was constructed for the coupling calculation of electromagnetic field and sound field. The simulation results verified that the sound pressure waveform at the detection point reflected the position of magnetic nanoparticles in biological tissue. Using the sound pressure data detected by the ultrasonic transducer, the B-scan imaging of the magnetic nanoparticles was achieved. The maximum error of the target area position was 1.56%, and the magnetic nanoparticles regions with different concentrations were distinguished by comparing the amplitude of the boundary signals in the image. Studies in this paper indicate that B-scan imaging can quickly and accurately obtain the dimensional and positional information of the target region and is expected to be used for the detection of magnetic nanoparticles in targeted therapy.