| Tracer-based medical imaging technology is a kind of imaging technology in the field of biomedical engineering,which can detect the distribution of tracers and then diagnose diseases,and is widely used in biomedical diagnosis in vivo.Among them,Magnetic Particle Imaging（MPI）is a new tracer-based tomography technology in recent years,which can quantitatively detect the spatial and concentration distribution of Magnetic Nanoparticles（MNPs）.In MPI,due to the superparamagnetic properties of MNPs,the MNPs located in the field free region will produce a nonlinear magnetization response under the action of an external alternating magnetic field.In order to match and image the particle signal with the spatial position,it is necessary to move the field free region in MPI.The research of scanning and control methods in field free region can improve the imaging speed and quality of MPI,which has important research value and significance.Firstly,according to the principle of MPI,a field free line electrically driven scanning method based on open-structure MPI system is proposed.Two groups of orthogonal planar gradient coils are used to generate field free line and realize the electrical rotation and layer selection operation of the field free line.At the same time,in order to maintain the open structure of the system,a pair of Helmholtz coils are added in the vertical direction to realize the electrical translation operation of the field free line,and the feasibility of the method is proved by simulation.Secondly,the field free fine electric drive scanning control method is designed,and the field free region scanning control system for open-structure MPI is completed.The control of the current module,the magnetic induction intensity measurement module and the temperature monitoring module of the system are controlled by the upper computer software,which drives the generation,translation and rotation of the field free fine.The uniformity and scanning error of the field free fine meet the imaging requirements.Finally,based on the frequency characteristics of MNPs,a single-side differential receiver coil for open structure MPI system is designed,and the effectiveness of this structure is verified by simulation.At the same time,based on the simulation parameters,a MPI system of field free line with open structure is designed and built,and the detection of nonlinear magnetization signal of MNPs and the two-dimensional imaging experiment of MNPs model are completed.The experimental results show that the translation distance and rotation angle of the field free line can be precisely controlled by changing the amplitude and direction of the current applied in the electromagnetic coil structure,and the detection of nonlinear magnetization signal of 1 mg/ml,40 nm particle size MNPs experimental model and two-dimensional imaging are completed in the MPI system with gradient of 0.1256 T/m,and the imaging resolution can reach9.5 mm.Therefore,the field free line scanning and control method for MPI proposed in this paper provides an accurate spatial encoding method and improves the imaging resolution of the open-structure magnetic particle tomography system. |
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