14T MRI Magnet Design And Optimization Of Magnetic Field Configuration

Magnetic resonance imaging(MRI)has two main directions of development:high magnetic field and high homogeneity.Since high magnetic field can greatly improve SNR and imaging resolution,high homogeneity and stable magnetic field can better achieve the synchronization of time and space to obtain fast and clear scanning;So as to explore the more limited functional information of organisms,study the role of intelligence,human brain consciousness and psychological and emotional incentives.Since China has been in the blank in high field magnetic resonance and seriously lags behind the development of foreign countries in this area,it is very necessary to timely carry out the research of 14T ultra high field magnetic resonance.The magnetic system of 14T is the core,and its magnetic field design requires the homogeneity of the central imaging area to reach the order of 10-6(PPM),and the distance of magnetic shielding 5Gs line should be within 15m as far as possible.For this reason,detailed electromagnetic optimization design and algorithm research are carried out in this paper.The requirement of MRI for the main magnet is to generate a magnetic field with high homogeneity and stability in a wide range of space.Therefore,the main magnet of the superconducting magnet was designed and improved.The Monte Carlo algorithm of the APDL probability design module was used to analyze the main parameter factors affecting the field uniformity of the main magnet,and the correlation data of the various variables on the results were constructed.The inhomogeneity of the main magnet was initially reduced from several thousand ppm to 65ppm with the multi-coil structure.The basic expression of passive static magnetic field is established,and the spherical harmonic components of the magnetic field are obtained.At the same time,three kinds of electromagnetic theories for magnetic field calculation of ring coils are established,and corresponding programs of various methods are written.The theoretical method and program of magnetic field calculation with the best efficiency are found.A design scheme of 14 T MRI magnets was presented by using the method of combined optimization of linear and nonlinear programming.By using the magnetic field point sampling method,the inhomogeneity in the spherical imaging area with a diameter of 22cm was reduced to lppm by applying 4 sets of coils,while the 5Gs line of high field dissipation was reduced to 13m through the magnet self-shielding method.Later on,by modifying the sampling optimization method to spherical harmonic series elimination,the inhomogeneity is reduced to 0.05ppm,while the 5Gs line is reduced to 11.5m.The calculation time is also reduced from 30min to 10min.,and the overall efficiency is greatly improved.