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

Imaging of magnetic nanoparticles with ultrasound utilizes ultrasound excitation and electromagnetic receiving. At present, the size of magnetic nanoparticles (MNPs) for the imaging method is required to be no less than 100 nm, which limits its application in human bodies. To overcome the limitation of particle size, imaging of MNPs with ultrasound based on saturation magnetization is proposed. The relationship between the concentration of superparamagnetic pear-shaped MNPs and the induced voltage under saturation magnetization is derived based on the classical Langevin theory of paramagnetism. A 3D simulation model is constructed and numerical research is carried out under the saturated magnetic field provided by the Helmholtz coil. The concentration image is reconstructed by point-by-point scanning. Numerical studies show that the induced voltage is rich in the concentration information of superparamagnetic pear-shaped MNPs, proving the feasibility of the method. The maximum induced voltage, which enhances the imaging effect, occurs under the minimum radius of the detection coil containing the region of interest. MNPs under 20 nm still meet the imaging requirements in the proposed method. This research pushes the imaging of MNPs with ultrasound based on saturation magnetization a further step forward to practical applications in the biomedical field.