Design And Research Of Shimming Coils And Gradient Coils In Magnetic Resonance System

Magnetic resonance system is one of the most important scientific instruments,which is widely used in many research fields,such as chemistry,biology,medicine and so on.To our knowledge,magnetic resonance systems can be roughly divided into two categories:nuclear magnetic resonance(NMR)spectrometer and magnetic resonance imaging(MRI)system.The performance of the magnetic resonance system largely depends on the homogeneity of the main magnetic field B0 and the properties of the gradient field.The shim coil can improve the homogeneity of the main magnetic field and the gradient coil can produce a linear gradient field,Which are the two key components of the magnetic resonance system.Research and design of the shim coil and gradient coil is always hotspot and difficulty of the research in magnetic resonance system.For a different magnetic resonance system,we should provide different shim and gradient coils.This dissertation has carried out as follows:(1)Taking into account the structural differences between different types of magnets,the finite difference stream function method is improved.The finite difference equations and regularized constraint matrix are constructed in a targeted manner,and the shim and gradient coil suitable for flat magnets,cylindrical magnets and Halbach magnets are calculated.The electromagnetic field simulation is performed on the above coils arising from theoretical calculation,and the simulation results indicate that the finite difference stream function method can be used to design the shim coil.(2)In order to verify the effectiveness and practicability of the improved and optimized finite difference stream function method,a set of home-made shim-gradient dual-function coils for a flat-type system were manufactured according to theoretical calculation.Finally,the experiments of shimming and MRI for this dual-function coil were carried out on a home-built 0.06T low-field magnetic resonance system.The test sample adopts 10mm tube with an aqueous solution.After shimming,the 1H NMR spectrum peak width at half-height can be narrowed from 120Hz to 20Hz,which significantly improves the homogeneity of the magnetic field.In MRI experiments,we can obtain a clear and non-distortion MRI image of the sample.These experimental results show that the shim and gradient coils designed and manufactured can work perfect in fact.Which means the improved and optimized finite difference stream function method is suitable for practical applications.