Research Of Magnetic Particle Imaging System Based On Superparamagnetic Iron Oxide Nanoparticles

Magnetic Particle Imaging(MPI)technology is an imaging method that directly detects magnetic nanoparticles.It has broad application prospects as a safe substitute for iodine or gadolinium contrast agents due to its sensitivity and resolution.The principles of MPI imaging can be described using Langevin theory.The non-linear magnetization response is generated by exciting superparamagnetic iron oxide nanoparticles(SPION)in an alternating magnetic field,which appears as an alternating voltage in the receiving coil,and then collects data for later imaging processing through data acquisition.In the MPI system,the magnetization behavior of SPION can be resolved by Langevin theory,which mainly stimulates SPION by the FFP without magnetic induction formed by the gradient magnetic field.The magnetized SPION can be characterized as magnetized unsaturated and saturated states at different distances from FFP,and the above two states can make SPION to generate a non-linear magnetization response and not produce non-linear magnetization response to distinguish the SPION distribution information.In this paper,The superparamagnetic physical properties of magnetic nanoparticles smaller than 100 nm are drawn from the paramagnetic principle of magnetic substances.Then the principle that the particles generate nonlinear magnetization response is calculated and analyzed from the theoretical level using Langevin theory,including the setting of the gradient magnetic field and the excitation magnetic field in the entire MPI system,and the selection of parameters such as particle concentration and particle size.The non-linear magnetization response and time domain signals generated by the magnetic particles are observed and analyzed.Then,the gradient values of different particle concentrations,particle sizes,and gradient magnetic fields are respectively set in the simulation environment to simulate and analyze the time domain signals of the particles in order to select the appropriate concentration,particle size,and gradient magnetic fields as parameters of the hardware system.Then,the X-space principle employed in this paper is analyzed in detail,and the distribution of particles is directly reconstructed by using SPION time domain signals.The basic structure of SPION time-domain signal and the conclusion that the odd harmonics occupy the main part from the frequency spectrum are determined through simulation.Subsequently,the MPI hardware system was constructed,in which field programmable gate array(FPGA)controllers were employed to replace discrete equipments such as oscilloscopes and signal generators employed in ordinary laboratories.The excitation signal is amplified using a power amplifier to meet the requirements of the strong current intensity on the excitation coil,which drives the FFP to traverse the field of view(FOV).The non-linear magnetization response generated by SPION is coupled through the designed canceling receiving coil.The excitation magnetic field and the gradient magnetic field are constructed according to the simulation results of the parameters of the two magnetic fields according to the electromagnetic simulation environment.The preamplifier and filter are then designed to meet the acquisition requirements of the analog-to-digital converter(ADC)and further improve the signal-to-noise ratio(SNR).The signal is collected and transmitted through the FPGA control board to further save the obtained SPION time domain signal.Finally,the distribution of particles was simply located and 2D image reconstruction was performed to verify the feasibility of the system by processing the data.