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Gradient shimming based on regularized estimation for B(0)-field and shim functions.

Kan Song1, Qingjia Bao2, Fang Chen2

  • 1State Key Laboratory of Magnetic Resonance and Atomic Molecular Physics, Wuhan Center for Magnetic Resonance, Key Laboratory of Magnetic Resonance in Biological Systems, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China; University of Chinese Academy of Sciences, Beijing 100049, China.

Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|May 2, 2016
PubMed
Summary

This study introduces a new regularized estimation method for magnetic field mapping in gradient shimming. The technique improves field map quality and shimming results, especially in low-homogeneity conditions.

Keywords:
B(0) inhomogeneityField mappingGradient shimmingNMR spectrometerPenalized Maximum LikelihoodRegularized estimation

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Area of Science:

  • Magnetic Resonance Imaging
  • Medical Physics

Background:

  • Spatially mapping B0-field and shim functions is essential for gradient shimming.
  • Conventional phase difference imaging methods are susceptible to noise and T2(*) effects, leading to inaccurate field maps.

Purpose of the Study:

  • To develop a novel gradient shimming method using regularized estimation for B0-field and shim functions.
  • To enhance the accuracy and quality of magnetic field mapping in MRI.

Main Methods:

  • A statistical model and Penalized Maximum Likelihood method were employed.
  • Two regularized least-squares cost functions were minimized for B0-field and shim function estimation.
  • The method accounts for Gaussian noise in phase difference measurements and the smoothness of B0-field maps, incorporating spherical harmonic properties for shim functions.

Main Results:

  • The new method significantly improves the quality of field mapping compared to conventional techniques.
  • Enhanced shimming results were achieved, particularly in scenarios with poor magnetic field homogeneity.
  • Computer simulations and experimental data validated the effectiveness of the proposed approach.

Conclusions:

  • Regularized estimation offers a robust solution for B0-field and shim function mapping in gradient shimming.
  • This approach overcomes limitations of traditional methods, providing more accurate and reliable field maps.
  • The technique holds promise for improving MRI performance, especially in challenging magnetic field environments.