Pole Shape Optimization Of NMR Imaging Main Magnet

The device of NMR imaging is a sort of equipment of advanced medical diagnosis, which can acquire the transected scanning imaging of interior tissue of human body. Using permanent magnet as the main magnet, which is the core of NMR imaging device, is the current trend. The edge effect of the main magnet influences the imaging quality seriously. The thesis is devoted to the pole shape optimization in order to improve the homogeneity of the magnetic field in a large imaging volume between the poles.At the beginning the thesis indicates the crux of NMR imaging is the homogeneity of the static magnetic field through introducing the basic principle of NMR imaging and presents the requirement of the satisfying imaging. The permanent main magnet is mainly the developing direction through analyzing the advantages and disadvantages between three sort of main magnets : superconductor, routine and permanence.Aiming at the different types of the permanent main magnet with edge effects, which can't reach the demand of NMR imaging, numerical method of magnetic field computation and the theory of shape optimization is applied. Base on certain main magnets of NMR this thesis designs the most excellent structure of the pole shape and obtains a relatively uniform magnetic field in a large imaging volume.The calculating model of pole shape made of pure iron can be simplified with the infinite permeability and calculated with the scalar potential. The rule between pole shape and the homogeneity or the size of uniform region of magnetic field is discovered and factors of influencing the homogeneity of the magnetic field are held so that the main magnet with the optimized size of pole shape can produce a relatively uniform magnetic field in a large imaging volume.Following the optimization of the pole shape the highly homogeneity in a larger volume is obtained, which is based on the improved genetic algorithm as searching tools and on the finite element method as scheme appraisement.At last, the experiment for the mini-device of NMR imaging, which is finished together with the relative company, proves the efficiency of the optimized schemes of pole shape presented in this thesis.