Passive Shimming by Eliminating Spherical Harmonics Coefficients of all Magnetic Field Components Generated by Correction Iron Pieces

Noguchi, So; Kim, Seokbeom; Hahn, Seungyong; Iwasa, Y.

doi:10.1109/tmag.2013.2276736

Cited by 12 publications

(7 citation statements)

References 10 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…13,[16][17][18]21,22 The spherical harmonic coefficients presented in this paper facilitate active shimming for various kinds of coils by eliminating the higher terms of the entirecomponent coefficients than the 0th one. On the other hand, in the case of passive shimming, it is difficult to eliminate the higher terms of the coefficients.…”

Section: Discussionmentioning

confidence: 99%

“…The result of passive shimming in the previous paper 21 was obtained using the formulas (38)-(48) presented in this paper, the magnetic moment method, 23,24 the rotation transform, 25 and the genetic algorithm. 26,27 The developed technique will be applied to more complicated magnet, such as an open type MRI and a racetrack magnet of accelerator, for active and passive shimming.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Formulation of the spherical harmonic coefficients of the entire magnetic field components generated by magnetic moment and current for shimming

Noguchi

2014

Journal of Applied Physics

Self Cite

View full text Add to dashboard Cite

For MRI and NMR magnet design, a highly homogeneous and high magnetic field has to be achieved by active and/or passive shimming. The active and passive shimming commonly homogenize the magnetic field around the magnet center by cancellation of the higher terms of a spherical harmonic series than the 0th term. So far, the spherical harmonic expression in the cylindrical coordinate system is well known for a circular coil, a solenoid coil, and magnetization of ferromagnetic material with/without its volume. In a shimming design, only the z-component of an inhomogeneous magnetic field is compensated because it is dominant to the performance of MRI/NMR. However, various kinds of MRI and NMR systems have recently been developed, and these magnets sometimes have an axially asymmetric configuration or generate a tilted magnetic field. Therefore, the entire x-, y-, and z-components have to be homogenized for such magnets. I derive the spherical harmonic expression of the entire components of magnetic field generated by a circular coil, a dipole coil, and a straight line current. In addition, since the entire magnetization components of the ferromagnetic material having the volume contribute the entire components of the magnetic field around the magnet center, I also derive the equations of the spherical harmonic coefficients of the magnetic field generated by ferromagnetic material. Since these equations need a numerical integration, such as the Gauss quadrature integration, the computation accuracy of the spherical harmonic coefficients is investigated against the number of the evaluation points. We can calculate the highly accurate spherical harmonic coefficients with the small number of the evaluation points. (C) 2014 AIP Publishing LLC

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Formulation of the spherical harmonic coefficients of the entire magnetic field components generated by magnetic moment and current for shimming

Noguchi

2014

Journal of Applied Physics

Self Cite

View full text Add to dashboard Cite

show abstract

“…The coefficients C s and D s are obtained from the numerical integration with respect to the volume of the correction iron piece and shown in [7]. …”

Section: B Spherical Harmonics Coefficients By Magnetic Momentmentioning

confidence: 99%

Passive Shimming for Magic-Angle-Spinning NMR

Noguchi

Hahn

Iwasa

2014

IEEE Trans. Appl. Supercond.

Self Cite

View full text Add to dashboard Cite

Abstract-The superconducting dipole magnets wound with HTS wires have been developed for a magic-angle-spinning NMR. The magnetic field of the dipole magnets is tilted from z-axis. Since the highly homogeneous magnetic field is required, the magnetic field of the dipole magnets is necessarily compensated by passive and/or active shimming. However, the compensation of all the components has not been reported. Usually, due to the axial symmetry of a solenoid magnet, only z component of the magnetic field is homogenized. In this paper, all the x, y, and z components of the magnetic field generated by the superconducitng dipole magnet are compensated because of the tilt from the z-axis.

show abstract

“…The iron pieces are magnetized passively due to the strong magnetic field and the magnetized iron pieces have magnetic moments (MMs) which generate a magnetic field to correct error fields. 6 – 13 The active shimming uses small coils (shim-coils) and many shim-coils are necessary for accurate shimming with an increased magnet cost. However, the shim-coils for the active shimming can also be considered to have MMs by applied currents, and the MMs generate correcting magnetic fields.…”

Section: Introductionmentioning

confidence: 99%

Passive Shimming of MRI Static Magnetic Field Using Regularization of Truncated Singular Value Decomposition

Abe¹

2017

magn reson med sci

View full text Add to dashboard Cite

Purpose:To develop a new shimming calculation method, which can calculate iron piece placements rapidly to make the magnetic field homogeneous at intended homogeneity and then to make the shimming working time short.Materials and Methods:The shimming calculation yields magnetic moment (MM) distribution, which is calculated by the truncated singular value decomposition (SVD) from the measured magnetic field. The MM distribution is described by a superposition of eigenmodes obtained by SVD of a response matrix from the moment distributions to magnetic fields at the field of view (FOV). The homogeneity is regulated by a truncation number of the superposed eigenmodes. The magnetic moments are converted into iron volumes with the assumption of saturated magnetization and the iron pieces are placed according to the calculation results. Since the SVD calculation can be done in advance, the computational time at the shimming site is short.Results:Trial applications on a 0.5T magnetic resonance imaging (MRI) magnet were done using the new shimming calculation method, which was proved to work well. However, since the iron piece volumes had tolerances, the work was repeated until enough homogeneity was obtained. As a result, an intended homogeneity of 8.9 ppm (peak-to-peak) on 40 cm diameter spherical surface was successfully obtained from measured homogeneity of 543 ppm with short computational and working time.Conclusion:The test shimming work showed that the developed shimming calculation method with truncated SVD regularization is applicable to the shimming work on the MRI magnets.

show abstract

Passive Shimming by Eliminating Spherical Harmonics Coefficients of all Magnetic Field Components Generated by Correction Iron Pieces

Cited by 12 publications

References 10 publications

Formulation of the spherical harmonic coefficients of the entire magnetic field components generated by magnetic moment and current for shimming

Formulation of the spherical harmonic coefficients of the entire magnetic field components generated by magnetic moment and current for shimming

Passive Shimming for Magic-Angle-Spinning NMR

Passive Shimming of MRI Static Magnetic Field Using Regularization of Truncated Singular Value Decomposition

Contact Info

Product

Resources

About