• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2001.02a
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• pp.121-124
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• 2001

The research results on the superconducting magnet for whole body MRI are presented. The magnet consists of main coil with 6 solenoid coils, shielding coil with 2 solenoid coils and 6 sets of cryogenic shim coil. The ferromagnetic shim assembly is installed on the inside wall of the room temperature bore for shimming inhomogeneous field components generated due to manufacturing tolerances, installation misalignments and external ferromagnetic materials near the magnet. Also, the magnet is enclosed with the horizontal type cryostat with 80cm room temperature bore to keep the magnet under the operating temperature. The magnetic field distributions within the imaging volume were measured by the NMR field mapping system. Through the test, the central field of magnet was 1.5 Tesla and the field homogeneity of 9.3 ppm has been obtained on 40cm DSV(the diameter of spherical volume) and using this magnet, comparatively good images for human body, fruits and water phantoms have been achieved.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.37 no.8
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• pp.521-527
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• 1988

At present superconducting magnets have been feasible for many applications which require high field or highly homogeneous field that it is too difficult to be produced by conventional electromagnets. This paper is a stuny on Donble Helmholtz superconducting magnet and newly configurated superconducting magnet that realize highly homogeneous field with the minimum magnet volume. Nonlinear programming method is effectively used for the minimum volume of superconducting magnet that realizes the desired field intensity and high homogeneity. The results on Double Helmholtz and newly configurated superducting magnets that are presented in this paper are largely improved.

• Journal of Electrical Engineering and Technology
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• v.1 no.4
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• pp.461-465
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• 2006

This paper presents a useful and simple method to design the passive skimming system for homogeneous permanent magnets based on numerical optimization. To simulate the effects of manufacturing and assembling tolerances, the actual geometrical parameter of the magnet with a derivation is suggested. Then, the optimal design model oi a passive shim system is set up to correct the derivative of field homogeneity. The numbers, sizes and locations of the passive shims are optimized by the steepest descent algorithm combined with design sensitivity analysis. Two implementations show that the proposed method can achieve the required homogeneity of the field with the minimum quantity of ferromagnetics.

• Progress in Superconductivity and Cryogenics
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• v.14 no.1
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• pp.14-19
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• 2012

Shimming, active and/or passive, is indispensable for most MR (magnetic resonance) magnets where homogeneous magnetic fields are required within target spaces. Generally, shimming consists of two steps, field mapping and correcting of fields, and they are recursively repeated until the target field homogeneity is reached. Thus, accuracy of the field mapping is crucial for fast and efficient shimming of MR magnets. For an accurate shimming, a "magnetic" center, which is a mathematical origin for harmonic analysis, must be carefully defined, Although the magnetic center is in general identical to the physical center of a magnet, it is not rare that both centers are different particularly in HTS (high temperature superconducting) magnets of which harmonic field errors, especially high orders, are significantly dependent on a location of the magnetic center. This paper presents a new algorithm, based on a field mapping theory with harmonic analysis, to define the best magnetic center of an MR magnet in terms of minimization of pre-shimming field errors. And the proposed algorithm is tested with simulation under gaussian noise environment.

• Proceedings of the KIEE Conference
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• 2001.04a
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• pp.22-25
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• 2001

The research results on the superconducting magnet for whole body MRI are presented. The magnet consists of main coil with 6 solenoid coils, shielding coil with 2 solenoid coils and 6 sets of cryogenic shim coil. The ferromagnetic shim assembly is installed on the inside wall of the room temperature bore for shimming inhomogeneous field components generated due to manufacturing tolerances, installation misalignments and external ferromagnetic materials near the magnet. Also, the magnet is enclosed with the horizontal type cryostat with 80cm room temperature bore to keep the magnet under the operating temperature. The magnetic field distributions within the imaging volume were measured by the NMR field mapping system. Through the test, the central field of magnet was 1.5 Tesla and the field homogeneity of 9.3 ppm has been obtained on 40cm DSV(the diameter of spherical volume) and using this magnet, comparatively good images for human body, fruits and water phantoms have been achieved.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 1999.02a
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• pp.113-116
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• 1999

The shield effects of the actively shielded superconducting magnet systems for MRI were investigated. The magnetic field was calculated by FEM considering the winding error and the homogeneity of the magnetic field at the 30cm DSV was presented. The 5 gauss stray field line was restricted within 5m form the magnet center.

• Progress in Superconductivity and Cryogenics
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• v.22 no.1
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• pp.12-16
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• 2020

As high homogeneity in magnetic field is required to increase the resolution of MRI magnets, various shimming methods have been researched. Using one of them, the design of the superconducting active zonal shim coil for MRI magnets is discussed in this paper. The magnetic field of the MRI magnet is expressed as the sum of spherical harmonic terms, and the optimized current density of shim coils capable of removing higher-order terms is calculated by the Tikhonov regularization method. To investigate all potential designs derived from calculated current density, 4 sweeping parameters are selected: (1) axial length of shim coil zone; (2) radius of shim coils; (3) exact axial position of shim coils; and (4) operating current. After adequate designs are determined with constraints of critical current margin and homogeneity criterion, the total wire length required for each is calculated and the design with a minimum of them is chosen. Using the superconducting wire length of 9.77 km, the field homogeneity over 50 cm DSV is improved from 24 ppm to 1.87 ppm in the case study for 9.4 T whole-body MRI shimming. Finally, the results are compared with the finite element method (FEM) simulation results to validate the feasibility and accuracy of the design.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2001.02a
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• pp.178-181
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• 2001

Two methods can be used to correct the undesirable magnetic field of MRI. One is active shimming method and the other is ferro-magnetic shimming. Ferro-magnetic shimming method is more inexpensive, more convenient in operation and more effective on correcting magnetic field. So, nowadays, it is the general method for shimming the commercialized MRI magnet. We have developed a 1.5T MRI magnet and its ferromagnetic shimming system. Using the ferro-magnetic shimming system, we have improved the field homogeneity of the 1.5T MRI magnet.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.817-818
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• 2006

A 2.0T class HTS conduction cooled magnet was designed. Designing of magnet shape was performed through two steps. First step is to find a basic cross section for minimize the amount of conductor used and second step to optimize the coil shape to satisfy the magnetic field homogeneity. The magnetic fields was analyzed with FEM and the critical current value of magnet was also expected with the result of field analysis and the Ic to B curve of Bi-2223 HTS tape.

• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.153-155
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• 1995

We fabricated superconducting magnet for MRI and tested it using automatic field mapping system. This magnet has 20cm diameter of room temperature bore for the sample access. In this paper, the fabrication of MRI magnet system and the test results of field homogeneity are described.