Research On Magnetic Field-Free Line Biological Magnetic Particle Imaging Method

Medical imaging technology is an imaging technology that can check and diagnose diseases in the field of biomedical engineering.Magnetic Particle Imaging(MPI)is a tracer imaging technology with high imaging resolution.MPI utilizes the non-linear magnetization characteristics of magnetic nanoparticle tracers in a magnetic field-free point to visualize the spatial distribution of tracer concentration in the test object.The coil structure and scanning of the MPI scanner determine its imaging resolution and imaging effect of the reconstructed image.Aiming at biological magnetic particle imaging,this paper proposes a magnetic field-free line scanning method.The key technical parts of MPI imaging are designed to improve the high resolution of the imaging system.First,the principle of MPI based on magnetic field-free line is studied.In view of the current open scanning problem of imaging systems,a high-resolution open magnetic field-free line is proposed,which provides the basic magnetic field for open two-dimensional scanning imaging.A gradient static magnetic field is used to construct a magnetic field-free line to determine the position of the tracer.A uniform alternating magnetic field and a changing gradient static magnetic field are used to achieve magnetic field-free line translation and rotation scanning.A detailed design and analysis of the coil structure was carried out to determine the current drive method to realize the high-resolution MPI coil system.Secondly,based on the nonlinear magnetization characteristics of magnetic particles and the frequency characteristics of their magnetization,a third harmonic differential detection method for magnetic particle signals is proposed.Through modeling and simulation,the nonlinear magnetization response characteristics of magnetic particles under alternating field and the frequency spectrum characteristics of magnetic particle signals were studied.On this basis,build a signal detection experiment system,analyze the spectrum characteristics and power spectral density of the detected signal,and study the relationship between the signal and excitation frequency.Finally,the magnetic field-free line field MPI method is simulation analyzed and imaged.Based on the simulation and analysis of the central magnetic field,scanning performance and resolution in the magnetic field-free line,a numerical model of the received signal was established,and a back projection reconstruction method for two-dimensional scanning of particle concentration was designed to achieve particle concentration for different targets The model's markers reconstruct the image.The simulation and imaging experiment results show that: under the alternating excitation field,the magnetic nanoparticles produce a spike signal higher than the background signal,and the magnetic nanoparticle signal exists in the odd harmonics of the detection signal spectrum,and its spectral energy is concentrated in the third harmonic At the wave,it can realize the detection of the third harmonic magnetic particle signal that meets the needs of medical detection.At the same time,the simulation results prove that the open magnetic field-free line designed in this paper can meet the needs of magnetic particle imaging.In the gradient magnetic field of 1.316 T / m,high-resolution imaging of magnetic nanoparticle tracer within the imaging area of 17 mm × 17 mm can be achieved,and its resolution can reach sub-millimeter level,and can clearly distinguish different sizes,The concentration model of magnetic nanoparticles in different positions and different concentrations theoretically proves the feasibility of the open magnetic field-free line scanning method for MPI.