Gradient Coil Design Of Superconducting Magnetic Resonance Imaging System

Magnetic resonance imaging(MRI)is a promising medical imaging technology.Gradient coils are important components of the MRI system,which are used to generate gradient magnetic fields that vary linearly in three orthogonal directions in the imaging region,and encode the spatial information of the imaged object.Gradient coils include transverse and longitudinal gradient coils,and the performance of the gradient coil directly affects the imaging quality of the MRI system.In this paper,the regularization method is used to design the transverse self-shielded gradient coils of superconducting MRI system.The Fourier coefficient expansion is performed on the current density of the main coil and the shield coil of the gradient coil respectively,and the magnetic field deviation of the imaging region and the shielding region is used as the optimization objective function.The Tikhonov regularization method is adopted to introduce the gradient coil power loss as a penalty function.The current density is discretized by the stream function method to obtain the winding form of the gradient coil,and the design of the self-shielding gradient coil is completed.When the gradient coil works with a large current,the gradient coil winding will generate a hot spot temperature in the system.The performance of the coil will be affected or even be damaged with a high hot spot temperature.Calculating the temperature distribution of the coil can be used to find the optimal position of the cooling tube when the gradient coil is made up.The vertical self-shielded gradient coil is designed in a similar way to the transverse gradient coil design.From the design results,we found that the gradient coil has too small coil spacing,which is not conducive to the production of the gradient coil.In order to solve this problem,a 0-1 integer programming method has been proposed for the design of longitudinal self-shielded gradient coils,in which the coil's former is divided into several one-dimensional grids,the volume of coil taken as the objective function.The optimal solution is found with the constraints of the nonlinearity of the gradient magnetic field in the imaging region,the magnetic field of the shielding region and the coil spacing,and the position distribution of the gradient coil along the axial direction of the magnet is obtained finally.