Simulation research on the forward problem of magnetoacoustic concentration tomography for magnetic nanoparticles with magnetic induction in a saturation magnetization state

Abstract

Magnetoacoustic concentration tomography of magnetic nanoparticles (MNPs) with magnetic induction (MACT-MI) is a method that has been propsed recently for MNP concentration tomography for use in targeted therapy. This procedure has the advantages of being noninvasive, having high-resolution and providing quantitative estimation of MNPs. In order to further fundamentally increase the signal-to-noise ratio of the magnetoacoustic signal, the forward problem of MACT-MI in the saturation magnetization state was studied, especially the magnetization characteristics of MNPs, including the derivation of the force formula of MNPs in the saturation magnetization state and the relationships among the gradient of the external magnetic field, magnetic force, number concentration and sound pressure. Firstly, the magnetic force formula of MNPs in the saturation magnetization state was derived according to the classical Langevin theory of paramagnetism. Then, a 2D model was constructed to calculate the magnetic flux density, magnetic force and sound pressure. Finally, the 2D distribution diagram of magnetic force and sound pressure and its corresponding 1D curve were obtained. The simulation results showed that the saturation magnetic field produced by the Maxwell–Helmholtz coils made the MNPs magnetically saturated. Compared with the MNPs in an unsaturated magnetization state, the magnetic force of MNPs in the saturation magnetization state was stronger, and the stronger magnetic force could generate stronger magnetoacoustic signals, which made it possible to measure magnetoacoustic signals with higher signal-to-noise ratio. The research results can provide a research basis for the design of equipment for further MACT-MI experiment and clinical application.

Numerical study on imaging of magnetic nanoparticles with ultrasound based on saturation magnetization

“…According to the classical Langevin theory of paramagnetism [13,14], the relationship between the magnetization of MNPs and the external magnetic field is a nonlinear Langevin function which is shown in figure 4. After the superparamagnetic pear-shaped MNPs reached the saturation magnetization state under a saturated magnetic field, all superparamagnetic pear-shaped MNPs are arranged in the same way without the influence of external force, and the spatial orientation of the intrinsic magnetic moment follows the direction of the external magnetic field.…”

“…When a pair of currents of same magnitude and direction are applied to the Helmholtz coils, the magnetic field in the z-direction can be expressed as [14]:…”

Simulation Research on Forward Problem of Magnetoacoustic Concentration Tomograghy of Magnetic Nanoparticles With Magnetic Induction Based on Multi-Coils

“…The electromagnetic parameters of the breast numerical model are shown in Table 3 [20][21][22]. Since the Maxwell coil and the six-coil structure designed in this paper will generate a zero magnetic field point in its central area [23], the center of the numerical model of the breast is set at (0, 10). In order to analyze the electromagnetic field instantaneously, the pulse current of multiple coils is passed through.…”

Simulation Research on Magnetoacoustic Concentration Tomography With Magnetic Induction Based on Uniaxial Anisotropy of Magnetic Nanoparticles

“…In 2021, Yan et al used Maxwell-Helmholtz coil to saturate MNPs. Compared with unsaturated magnetized MNPs, the saturated magnetized MNPs had stronger magnetic force [19]. They adopted the method of moments (MoM) to reconstruct the concentration distribution and proposed that there is a negative correlation between the quality of the reconstructed image and the radius of the imaging target [20].…”