Study On The Design Of Gradient Coils For Open MRI System

In recent years,with the continuous development of magnetic resonance imaging(MRI),more urgent requirements have been put forward for high-quality imaging and rapid imaging.As an important part of MRI,the gradient system provides a three-dimensional orthogonal gradient field for nuclear magnetic resonance signals to complete its spatial coding.With the advancement of various imaging techniques,higher requirements are imposed on the gradient field intensity and the gradient field switching rate.Therefore,this paper proposes an improvement for gradient coil design methods and processing techniques to improve the overall performance of gradient coils.In view of the existing problems in the existing gradient coil manufacturing process flow,the processing complexity is high,it is difficult to process gradient coils with complex shapes,and the manufacturing process is likely to cause performance degradation of the design results.A 3D printing process is adopted to perform gradient coil processing.Using 3D printing technology to produce gradient coils,the coils produced have high precision,and the gradient coils produced have a high degree of matching with the design results,and can fully utilize the skeleton space.The operation is very simple.The lateral gradient coil is designed by using the improved target field method.The surface current density function is developed in the form of a trigonometric function.The homogeneity of the gradient field is taken as the goal,and the objective function is established with the coil energy storage and power consumption as constraints.After the surface current density distribution is obtained,the flow function method is used to conduct the wire dispersion to obtain the final gradient coil shape.The calculation process uses the MATLAB platform,and then the distribution data of the conductors is used to establish a three-dimensional model using CAD,and COMSOL finite element simulation software is used for simulation experiments.The results show that the designed gradient coil meets the design requirements.An improved genetic simulated annealing algorithm is used to design the longitudinal gradient coils,which combines the powerful global optimization ability of the genetic algorithm with the "climbing ability" of the simulated annealing algorithm.Firstly,the coding method is improved so that the position and number of turns of the loop coil are used as optimization variables at the same time.Secondly,the Metropolis criterion is improved.When the annealing temperature is high,the global optimization ability of the algorithm is enhanced,and when the temperature is low,it is enhanced the local search ability of the algorithm.Experimental results show that the designed gradient coil satisfies the requirements and verifies the correctness and accuracy of the algorithm.