Development of an Open 0.3 T NdFeB MRI Magnet

An open 0.3 T NdFeB whole-body MRI magnet was developed which has a wide-access configuration. In order to obtain a high uniformity of magnetic field, a two-dimensional (2D) axisymmetric hybrid boundary element method (BEM)-integral equation method (IEM) was firstly employed for the magnet design, emphasizing on the optimization of the shape of the iron pole plates. An asymmetric two-column iron yoke was then designed by use of the three-dimensional (3D) ANSYS code. Both designed and measured data of the magnet are presented. To reduce the effect of induced eddy currents in the pole plates by pulsed gradient fields, a couple of specially-designed steel sheets were fixed on the pole plates. Experimental data showed that the delay of the built-up of gradient fields was improved remarkably. By passive shimming, a field homogeneity of 26 ppm on a 30 cm DSV (diameter spherical volume) was finally obtained.