Studies On The Method Of Designing Gradient Coils

In1973, Lauterbur and Mansfield first did imaging experiment for MRI studies. Since then, MRI has become equal and even better compared to X-ray, CT, ultrasound imaging and PET in imaging techniques. Over the past decades, great progress has been made in medical application of MRI. In terms of MRI hardware configure, the imaging apparatus chiefly consists of the following core parts:main magnet, gradient coils, RF coil, the spectrometer control system, amplifier circuits, etc... There is a considerable gap between domestic level and world top level in MRI scanner design and manufacture. In this paper, studies on the gradient coil design were presented and we hope these studies could be helpful for researchers and engineers in this field.The first part of the thesis introduced the function of the gradient coils in MRI, how to design gradient coils, as well as how to evaluate the performance of the gradient coils. Also in this part the designing, manufacturing and performance testing of gradient coils will be discussed.The second section describes the design method of the insertable bi-planar gradient coil. Scaling frequency space was used to design optimize conventional planar gradient coil and the insertable bi-planar gradient coil. The secondary shielding coil design is based on stream function which is expanded with cosine bases. It’s described in details later. To further reduce eddy current, this thesis attempts to utilize the simulated annealing algorithm to optimize the shielding coil. Finally, this part will introduce a new design method based on ant colony algorithm. Ant colony algorithm is put forward in1996, but its use in the design of gradient coils has not been reported. Hence this thesis proposes a new way to design gradient coils.The third part describes the design of a finite length cylindrical gradient coil in which target field method and the current density constraints are combined.