A Practical Passive Shimming Design Method of all Magnetic Field Components for MRI

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Abstract
In a magnetic resonance system, the magnetic field homogeneity of the imaging area plays a crucial role in imaging quality. However, due to design tolerances and environmental magnetization, shimming is usually necessary to achieve highly uniform magnetic field. And passive shimming, one of the shimming methods, is a widely used technique that utilizes ferromagnetic materials to reduce B0 deviation. Some papers present field contribution of the shims only in the z-direction for the central DSV region, often ignoring the magnetic field in x- and y-directions. This will generate a problem: whether the addition of ferromagnetic shims would cause indelible field deviations for the background magnetic field (BG) in x and y directions, that prone to cause failure to the entire shimming operations. For this reason, this article applied a case study exploring the homogeneity of the BG fields in all the directions and using the ferromagnetic shims for shimming in these three scenarios. First, only the background field is considered. Second, the shims to only optimize the BG fields in the z direction as most literature suggests. And third, the shims optimize the entire three directions adopting our method. Based on this, a practical passive shimming design scheme is provided. Through the optimization, it is found that the new method not only significantly improves BG fields in all the directions, greatly reducing the deviation of tilt angle of the total magnetic field B0 relative to the z-axis, but also no more increases in design difficulty nor consumption of ferromagnetic materials which greatly improve efficiency for the entire shimming procedures. The design theory of this article is a practical method for magnetic resonance imaging (MRI) shimming, which has certain guiding significance for various MRI applications.
Funding Information
  • Talents Introduction Fund of Anhui University of Science and Technology (13230408)
  • Strategic Priority Research Program
  • Chinese Academy of Science (XDB25000000)

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