• Title/Summary/Keyword: field gradient

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Partial Solution for Concomitant Gradient Field in Ultra-low Magnetic Field: Correction of Distortion Artifact

  • Lee, Seong-Joo;Shim, Jeong Hyun
    • Journal of the Korean Magnetic Resonance Society
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    • v.24 no.3
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    • pp.66-69
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    • 2020
  • In ultra-low field magnetic resonance imaging (ULF-MRI), the strength of a static magnetic field can be comparable to that of gradient field. On that occasion, the gradient field is accompanied by concomitant gradient field, which yields distortion and blurring artifacts on MR images. Here, we focused on the distortion artifact and derived the equations capable of correcting it. Its usefulness was confirmed through the corrections in both simulated and experimental images. This solution will be effective for acquiring more accurate images in low and/or ultra-low magnetic fields.

Magnetic Field Gradient Optimization for Electronic Anti-Fouling Effect in Heat Exchanger

  • Han, Yong;Wang, Shu-Tao
    • Journal of Electrical Engineering and Technology
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    • v.9 no.6
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    • pp.1921-1927
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    • 2014
  • A new method for optimizing the magnetic field gradient in the exciting coil of electronic anti-fouling (EAF) system is presented based on changing exciting coil size. In the proposed method, two optimization expressions are deduced based on biot-savart law. The optimization expressions, which can describe the distribution of the magnetic field gradient in the coil, are the function of coil radius and coil length. These optimization expressions can be used to obtain an accurate coil size if the magnetic field gradient on a certain point on the coil's axis of symmetry is needed to be the maximum value. Comparing with the experimental results and the computation results using Finite Element Method simulation to the magnetic field gradient on the coil's axis of symmetry, the computation results obtained by the optimization expression in this article can fit the experimental results and the Finite Element Method results very well. This new method can optimize the EAF system's anti-fouling performance based on improving the magnetic field gradient distribution in the exciting coil.

Fast MR Imaging Technique by Using Locally-Linear Gradient Field (부분적인 경사자계를 이용한 고속 자기공명 영상촬영기법)

  • 양윤정;이종권
    • Journal of Biomedical Engineering Research
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    • v.17 no.1
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    • pp.93-98
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    • 1996
  • The purpose of this paper is to propose a new localized imaging method of reduced imaging time luting a locally-linear gradient. Since most fast MR(Magnetic Resonance) imaging methods need the whole $\kappa$-space(Spatial frequency space) data corresponding to the whole imaging area, there are limitstions in reducing the minimum imaging time. The imaging method proposed in this paper uses a specially-made gradient coil generating a local ramp-shape field and uniform field outside of the imaging areal Conventional imaging sequences can be used without any RF/gradient pulse sequence modifiestions except the change in the number of encoding steps and the field of view.

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Design of Z-directional gradient coil to improve gradient linearity for the nuclear magnetic resonace imaging(NMRI) (경사자장의 선형성 향상을 위한 핵자기공명 영상용 Z-방향 경사자기장 코일 설계)

  • Ko, Rock-Kil;Lee, Dong-Hoon;Baek, Seung-Tae;Kim, Song-Hui;Kwon, Young-Kil;Ryu, Kang-Sik
    • Proceedings of the KIEE Conference
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    • 1998.07a
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    • pp.235-237
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    • 1998
  • Gradient coil offers the spatial informations of sample or patient in Nuclear Magnetic Resonance Imaging(NMRI) and its gradient field linearity over the field of view(FOV) has many influence on the MR imaging. Accurate and good quality MR imaging can be acquired by the high gradient field linearity over the FOV. So it is an important part to design of gradient coil with good linearity in the wide imaging range. Usually, Z-directional gradient field is generated by using the Helmholtz type coil which is consisted of one-pair loop with anti-current path. It gets less about 40% linearity of the diameter spherical volume(DSV). In this study, we calculated optimized geometrical parameters of two-pair loop system to cancel odd terms up to $B_7$ included effectively. we also analyzed and compared the gradient field distribution and linearity of the common Helmholtz coil with them of the two-pair loop system.

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High-Order Surface Gradient Coil Design Using Target Field Approach

  • Lee, J.K.;Yang, Y.J.;Jeong, S.T.;Choi, H.J.;Cho, Z.H.;Oh, C.H.
    • Journal of Biomedical Engineering Research
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    • v.17 no.1
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    • pp.19-24
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    • 1996
  • The purpose of this paper is to design high-order (or radial) surface gradient coil (SGC), which can provide multi-dimensional spatial selection. Although the spatial Selection with High-Order gradienT (SHOT) can provide a 2-D selection with only one selective RF pulse, the high-order gradient pro- duced by conventional cylindrical-shape coils has not been clinically useful due to the large selection size caused by the limited radial gradient intensity. However, by using the proposed high-order SGCs located near the imaging region, the size of volume selection can be reduced to a clinically useflll size of 1-2 cm in diameter by applying stronger radial gradient field with much less gradient driving power. So far radial SGCs have been designed by using the field component method and may cause distortion in the selection shapes. In this paper, by using the target field approach for the coil design, selected volumes became almost circular. A 40 cm-by-40 cm $z^2$_surface gradient coil has been designed and implemented by using the target field approach. Phantom and volunteer studies have been performed Experimental results using spatially localized MRI show good agreement to the theoretically predicted behavior.

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STUDY OF GRADIENT SOLITONS IN THREE DIMENSIONAL RIEMANNIAN MANIFOLDS

  • Biswas, Gour Gopal;De, Uday Chand
    • Communications of the Korean Mathematical Society
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    • v.37 no.3
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    • pp.825-837
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    • 2022
  • We characterize a three-dimensional Riemannian manifold endowed with a type of semi-symmetric metric P-connection. At first, it is proven that if the metric of such a manifold is a gradient m-quasi-Einstein metric, then either the gradient of the potential function 𝜓 is collinear with the vector field P or, λ = -(m + 2) and the manifold is of constant sectional curvature -1, provided P𝜓 ≠ m. Next, it is shown that if the metric of the manifold under consideration is a gradient 𝜌-Einstein soliton, then the gradient of the potential function is collinear with the vector field P. Also, we prove that if the metric of a 3-dimensional manifold with semi-symmetric metric P-connection is a gradient 𝜔-Ricci soliton, then the manifold is of constant sectional curvature -1 and λ + 𝜇 = -2. Finally, we consider an example to verify our results.

Design of Cylindrical Magnetic Gradient field for NMR-CT (NMR-CT에서 원통좌표계를 구현하는 경사자계의 고안)

  • 이대행;이순칠
    • Journal of the Korean Magnetics Society
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    • v.2 no.2
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    • pp.132-139
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    • 1992
  • We have designed a magnetic field gradient useful for cylindrical imaging in NMR-CT. The direc¬tion of the designed field is parallel to the axis and the gradient in the radial direction of cylindrical coordinate is monotonically increasing. The ratio of the gradient in the radial and axial direction is greater than 10 near the center of coordinate. This ratio depends on solenoid length, the number of reverse current turns at center, and the amount of the reverse current. We built a gradient coil based on the numerical simulation and tested the field generated by NMR-CT. The resulting image matches with the theoretical expectation within 10% error. Since the data acquisition time of 1-D imaging is significantly shorter than 2-D imaging, it becomes possible to image much more dynamic objects by the use of this gradient field.

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Cross Correlated Effects of Radiation Damping and the Distant Dipolar Field with a Pulsed Field Gradient in Solution NMR

  • Chung Kee-Choo;Ahn Sang-Doo
    • Journal of the Korean Magnetic Resonance Society
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    • v.10 no.1
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    • pp.46-58
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    • 2006
  • With a simple pulse sequence ($\pi/2$-{gradient, duration T}-acquisition) in solution NMR, detected signal has slowly grown up to percents of the equilibrium magnetization. The source of this unusual resurrection of dephased magnetization after a crushed gradient is cross-correlated effects of radiation damping and the distant dipolar field, which has been demonstrated by a numerical simulation and theoretical analysis.

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A new gradient coil design technique for open magnetic resonance imaging systems (개방형 자기공명영상시스템용 경사자계코일의 새로운 설계기법)

  • Lee, Soo-Yeol;Park, Bu-Sik;Yi, Jeong-Han;Yi, Wan
    • Journal of the Korean Institute of Telematics and Electronics S
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    • v.34S no.1
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    • pp.72-79
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    • 1997
  • Most open magnetic resonance imaging systems have used the planar gradient coils whose inductances were minimized through the magnetic energy minimization procedure in the spatial frequency domain. Though the planar gradient coils have smaller inductance than conventional gradient coils, the planar gradient coils often suffer from their poor magnetic field linearity. Scaling the spatial frequencies of the current density function designed by the magnetic energy minimization, magnetic field linearity of the planar gradient coils can be greatly improved with small sacrifice of gradient coil inductance. We have found that the figure of merit of the planar gradient coils, defined by the gradient strength divided by the linearity error and the inductance, can be improved by proposed technique.

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