Passive shimming and shape optimization of an unconventional permanent magnet for MRI

An unconventional permanent magnet for magnetic resonance imaging (MRI) in which the shape of imaging region is required to be a thin slice instead of a spherical volume is presented in this paper. To improve the initial magnetic field uniformity in the slice, the shape optimization of iron pole face using genetic algorithms (GAs) is investigated. To bring the field homogeneity of imaging region further to an acceptable level, an improved passive shimming method that optimizes the thickness of shimming pieces at each given location is described. This method is helpful for the shimming process in the practical work.