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| Study on Induction Magneto-Acoustic Magnetic Particle Concentration Imaging Based on Conical Core Coils |
| Yan Xiaoheng, Wang Bing, Chen Weihua, Hou Xiaohan, Wang Yufei |
| Faculty of Electrical and Control Engineering Liaoning Technology University Huludao 125000 China |
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Abstract Based on the magneto acoustic coupling effect, inductive magnetic acoustic tomography (MACT-MI) is a novel technique for imaging magnetic nano particle concentration (MNPs). However, previous research indicates that the current MACT-MI necessitates the employment of a high-amplitude excitation source device to generate magneto acoustic signals. To enable the ultrasonic probe to detect these acoustic signals, passing a pulse current of approximately 200 amperes through a Maxwell coil with a radius of 0.4 meters imposes stringent requirements on hardware configuration and hinders the advancement of experimental work. This paper introduces a device composed of a Maxwell-Helmholtz coil and a conical iron core for generating magnetic fields. Compared to traditional MACT-MI excitation units, this device incorporates an additional time-varying gradient magnetic field component induced by the conical iron core within the region of interest (ROI). The iron core's design optimization enhances the magnetic field's intensity and gradient allowing MNPs to convert magnetic energy into acoustic energy more efficiently, amplifying the magneto acoustic signals and reducing the excitation source's required amplitude.
Firstly, the formula for the magnetic force acting on MNPs is derived, and the magnetic field distribution induced by the iron core in MACT-MI is analyzed. Secondly, three optimization objectives are identified: maximizing the magnetic induction intensity of the gradient magnetic field, the overall amplification intensity, and the simulated magnetic force. A multi-objective function is constructed, and the range of values for the decision variables is set. Then, the COMSOL simulation software is utilized to model and calculate all decision variables related to the iron core coil. Finally, constraint conditions are established after comprehensively considering the applicability and production cost of the iron core and coil. Two sets of optimized iron core dimensions are obtained by applying the harmony search algorithm to filter the decision variables.
COMSOL software is used to generate two-dimensional distribution maps and one-dimensional graphs of magnetic flux density, magnetic force, and sound pressure for the cylindrical and conical iron core coil models. Under identical excitation current conditions, the maximum magnetic induction intensity of the gradient magnetic field within the ROI for the cylindrical and conical iron core coils has increased by approximately 0.4 times and 6.9 times compared to the air-core coil. Furthermore, the axial magnetic field gradient has expanded by 0.2 times and 3 times, and the magnetic force experienced by the MNPs at the central position has intensified by 0.6 times and 10.4 times.
The single-sided conical iron core coil designed in this paper can significantly enhance the gradient magnetic field generated by the MACT-MI device, leading to a notable increase in the magnetic force experienced by MNPs and the acoustic pressure. However, although magnetic field focusing can amplify the magnetic field intensity and gradient in regions proximal to the iron core, it inevitably decreases the uniformity of the magnetic field distribution. In conclusion, this paper conducts an in-depth study on the design of MACT-MI imaging devices, marking a significant step towards the practical application of MACT-MI imaging technology in biomedicine.
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Received: 30 June 2024
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2025, Vol. 40 
