Research On Key Technologies Of Magnetic Particle Magnetic Field-free Imaging

Magnetic Particle Imaging(MPI)is a new type of tracer imaging technology with high sensitivity,high resolution and real-time imaging advantages.This technology uses the nonlinear magnetization characteristics of magnetic nanoparticles in magnetic field-free to track and quantify the spatial and concentration distribution of the particles to obtain quantitative images.The spatial resolution of MPI is determined by the fineness of the magnetic field-free,and the fineness of the magnetic field-free is affected by the spatial magnetic field gradient.When the MPI system is built,different system construction schemes will get different magnitudes of magnetic field gradients.Based on this imaging technology,this paper designs an MPI magnetic field-free line system based on ring magnet array,which can generate fine magnetic field-free line to improve the spatial resolution of MPI.Firstly,this paper designs a system based on the MPI spatial coding field and signal coding field.A static magnetic field structure that can generate a large magnetic field gradient is constructed.Combining it with a driving structure,a magnetic field-free line system is built.For this system,the static magnetic field structure based on the ring magnet array is designed,and the structure is designed in terms of the method of magnets to generate magnetic field.The static magnetic field structure uses the large gradient static magnetic field to construct the fine magnetic field-free line.Then the driving structure based on the Helmholtz coil and its driving methods are designed,and the structure is designed in terms of the method of the electrical scanning method.Meanwhile,the relationship between the magnetic field-free line scanning range and the driving current can be determined.Finally,a collection of magnetic nanoparticles is added to the driving structure and the particles parameters are defined according to Langevin theory.The electromagnetic properties of the particles under the driving magnetic field are analyzed.Secondly,this paper analyzes the performance indicators of the designed system based on related evaluation parameters such as spatial resolution.Firstly,the spatial uniformity of the magnetic field-free line is evaluated.Then the spatial resolution under different ambient temperatures,magnetic field gradients and particle sizes is discussed.Finally,the signal bandwidth requirements of the system are analyzed and the cut-off frequency is calculated.Finally,a particle signal detection platform based on Lab View is designed,and the particle signal is used for MPI reconstruction.According to the MPI signal encoding process,a signal detection platform including five parts of signal measurement and filtering is designed.Then the system matrix and X-Space reconstruction methods are compared,and the two methods are used to perform one-dimensional reconstruction of particle signals.Finally,a two-dimensional reconstruction is performed using the direct back-projection method.The experimental results show that the structure of selection magnetic field based on the ring magnet array can generate large magnetic field gradient.Using 30 nm magnetic particles as tracer,the system spatial resolution is 0.540 mm when the magnetic field gradient is 4.804T/m,and the cut-off frequency of-3 d B representing the signal bandwidth is 5.19 MHz.At this time,the magnetic field-free line can carry out translational scanning on the measured object within the range of 30 mm.It indicates that the magnetic field-free line system based on ring magnet array is feasible for high resolution magnetic particle imaging.