Three-Dimensional Optimization of Correction Iron Pieces for Open High Field MRI System

Kakugawa, S.; Hino, N.; Komura, Akiyoshi; Kitamura, Masashi; Takeshima, Hiroyuki; Yatsuo, T.; Tazaki, Hideo

doi:10.1109/tasc.2004.831019

Cited by 18 publications

(11 citation statements)

References 8 publications

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“…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%

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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

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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

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Section: Discussionmentioning

confidence: 99%

“…Kakugawa et al derived the spherical harmonic expression for the entire components of a magnetic moment. 18 The expression took into account the volume of ferromagnetic material piece, whereas only the z-component of the expression was given. The magnetic field of the magicangle-spinning NMR, however, tilts from the z-axis.…”

mentioning

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

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“…Passive shimming is often employed to compensate the magnetic field using some pieces of iron. Since the magnetic field homogeneity of a few PPM is required around the center of the MRI/NMR magnet, the spherical harmonics series expansion of the magnetic field is calculated on the design stage [2], [3].…”

Section: Introductionmentioning

confidence: 99%

“…When the magnetic field is compensated with passive shimming, the z component of the magnetic moment of correction iron is also considered so that only the z component of the magnetic field is homogenized around the center. In recent years, some kinds of MRI/NMR magnets whose shape is axially asymmetric have been developed but generate a homogeneous magnetic field in the z-direction [3], [5]. The generated magnetic field is also axially asymmetric, therefore all the components of the center magnetic field have to be compensated by shimming.…”

Section: Introductionmentioning

confidence: 99%

Passive Shimming for Magic-Angle-Spinning NMR

Noguchi

Hahn

Iwasa

2014

IEEE Trans. Appl. Supercond.

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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.

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“…The passive shimming, one of the shimming methods, is to compensate the magnetic field using some pieces of iron [1]- [3]. Since the magnetic field homogeneity of a few PPM is required around the magnet center, the spherical harmonics expansion of the magnetic field is usually employed [4], [5].…”

mentioning

confidence: 99%

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

et al. 2014

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When a magnet generating highly homogeneous magnetic field is designed, a shimming is required. The shimming is usually performed so that the magnetic field only in the axis direction is compensated by iron pieces and/or coils. The compensation is commonly achieved by eliminating the coefficients of the spherical harmonics expansion of the magnetic field generated by the main magnet. Some papers showed the coefficients of the spherical harmonics expansion in only the z-direction for passive shimming. However, recently some magnets generate a magnetic field tilted from the z-axis, such as a magic-angle-spinning NMR/MRI. It is, therefore, necessary to eliminate the coefficients of the spherical harmonics expansion in the x-and y-directions.

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Three-Dimensional Optimization of Correction Iron Pieces for Open High Field MRI System

Cited by 18 publications

References 8 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 by Eliminating Spherical Harmonics Coefficients of all Magnetic Field Components Generated by Correction Iron Pieces

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