The present invention relates to a method and system for adjusting a magnetic center field of a magnetic field generator in an MRI. One embodiment of the presenting invention relates to a magnetic field generator system having a magnetic center field. This embodiment comprises opposing posts and opposing yokes connected to the opposing posts, where at least one of the posts has a spacer. At least one permanent magnetic block is connected to at least one of the opposing yokes. Further, at least one spacer is formed in at least one of the posts, the yokes and/or the permanent magnetic block.