• Journal of Biomedical Engineering Research
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• v.20 no.5
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• pp.537-544
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• 1999

자기공명영상시스템의 경사자계코일을 영구자석의 자극에 부착할 경우 경사자계의 분포가 변하고 코일의 인덕턴스가 증가하는 현상이 생긴다. 본 논문에서는 이러한 자극효과를 고려하여 평면형 경사자계코일을 설계하는 방법을 제시하였다. 제사한 방법에는 자극 효과를 거울 전류로 모델링하였고, 모델링한 거울 전류를 고려하여 경사자계코일의 인덕턴스를 최소화하는 방법을 구했다. 또한 실제 상황과 가장 흡사한 자계 분포를 만들어주는 거울 전류의 크기를 구하기 위해 유한요소법을 적용하였다. 제시한 방법으로는 설계된 경사자계코일은 종래의 설계된 경사자계 코일에 비해 우수한 성능을 보였다.

• Proceedings of the KSMRM Conference
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• 1999.11a
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• pp.114-114
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• 1999

• Progress in Superconductivity and Cryogenics
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• v.19 no.1
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• pp.51-55
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• 2017

To obtain Nuclear Magnetic Resonance (NMR) measurement of membrane protein, an NMR magnet is required to generate high intensity, homogeneity, and stability of field. A High-Temperature Superconducting (HTS) magnet is a promising alternative to a conventional Low-Temperature Superconducting (LTS) NMR magnet for high field, current density, and stability margin. Conventionally, an HTS coil has been wound by several winding techniques such as Single-Pancake (SP), Double-Pancake (DP), and layer-wound. The DP winding technique has been frequently used for a large magnet because long HTS wire is generally difficult to manufacture, and maintenance of magnet is convenient. However, magnetic field generated by the slanted turns and the splice leads to field inhomogeneity in Diameter of Spherical Volume (DSV). The field inhomogeneity degrades performance of NMR spectrometer and thus effect of the slanted turns and the splice should be analyzed. In this paper, field gradient of HTS double-pancake coils considering the slanted turns and the splice was calculated using Biot-Savart law and numerical integration. The calculation results showed that magnetic field produced by the slanted turns and the splice caused significant inhomogeneity of field.

• Proceedings of the KSMRM Conference
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• 2003.10a
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• pp.103-105
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• 2003

After fifteen years of development, Magnetic Resonance (MR) technology for human imaging and spectroscopy is reaching a refined state with FDA approved 3T clinical products from Siemens, GE, and Philips. Broker has cleared CE approval with a 4T system. Varian supports a 4T system platform as well. Shielded magnets are standard at 3T from GE, Oxford, Magnex, and IGC. A shielded 4T whole body magnet is available from Oxford. Stronger switched gradients and dynamic shim coils, desired at any field, areespecially useful at higher static magnetic fields B0. In addition to the higher currents required for higher resolution slice or volume selection afforded by higher SNR, whole body gradient coils will be driven at increasing slew rates to meet the needs of new cardiac applications and other requirements. For example 3T and 4T systems are now being equipped with 2kV, 500A gradient coils and amplifiers capable of generating 4G/cm in 200msec, over a 67+/-cm bore diameter. High field EPI applications require oscillation rates at 1 kHz and higher. To achieve a benchmark 0.2 ppm shim over a 30cm sphere in a high field magnet, at least four stages of shimming need to be considered. 1) A good high field magnet will be built to a homogeneity spec. falling in the range of 100 to 150 ppm over this 30cm spherical "sweet spot" 2) Most modern high field magnets will also have superconducting shim coils capable of finding 1.5 ppm by their adjustment during system installation. 3) Passive ferro-magnetic shimming combined with 4) active, high order room temperature shim coils (as many as five orders are now being recommended) will accomplish 0.2 ppm over the 30cm sphere, and 0.1 ppm over a human brain in even the highest field magnets for human studies. Safety concerns for strong, fast gradients at any B0 field include acoustic noise and peripheral nerve stimulation. One or more of the mechanical decoupling methods may lead to quieter gradients. Patient positioning relative to asymmetric or short gradient coils may limit peripheral nerve stimulation at higher slew rates. Gradient designs combining a short coil for local speed and strength with a longer coil for coverage are being developed for 3T systems. Local gradients give another approach to maximizing performance over a limited region while keeping within the physiologically imposed dB0/dt performance limits.

• Investigative Magnetic Resonance Imaging
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• v.18 no.2
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• pp.107-119
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• 2014

Purpose : To efficiently evaluate phased array coil performance using a software tool box with which we can make visual comparison of the sensitivity of every coil element between the real experiment and EM simulation. Materials and Methods: We have developed a $C^{{+}{+}}$- and MATLAB-based software tool called Phased Array Coil Evaluator (PACE). PACE has the following functions: Building 3D models of the coil elements, importing the FDTD simulation results, and visualizing the coil sensitivity of each coil element on the ordinary Cartesian coordinate and the relative coil position coordinate. To build a 3D model of the phased array coil, we used an electromagnetic 3D tracker in a stylus form. After making the 3D model, we imported the 3D model into the FDTD electromagnetic field simulation tool. Results: An accurate comparison between the coil sensitivity simulation and real experiment on the tool box platform has been made through fine matching of the simulation and real experiment with aids of the 3D tracker. In the simulation and experiment, we used a 36-channel helmet-style phased array coil. At the 3D MRI data acquisition using the spoiled gradient echo sequence, we used the uniform cylindrical phantom that had the same geometry as the one in the FDTD simulation. In the tool box, we can conveniently choose the coil element of interest and we can compare the coil sensitivities element-by-element of the phased array coil. Conclusion: We expect the tool box can be greatly used for developing phased array coils of new geometry or for periodic maintenance of phased array coils in a more accurate and consistent manner.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.20 no.2
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• pp.187-198
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• 1990

Examinations of the temporomandibular joints were performed on a 1.5 Tesla magnetic resonance (MR) system. An MR surface receiver coil 3 inch in diameter was placed on plastic frame, the patient's head being placed in the frame so that the coil was pressed against the temporal region. In taking advantage of the magnetic resonance imaging that has been studied briskly till now, author obtained the images of parasagittal and paracoronal planes about the temporomandibular joint by using MPGR (Multi-Planar Gradient Recalled), GRASS (Gradient Recalled Acquisition in the Steady State), and CSMEMP (Contiguous Slice Multiple Echo, Multi-Planar), that differ from the Spin Echo pulse sequence which the previous authors used. Five subjects with no symptoms of temporomandibular joint pain and dysfunction were studied. The plane images obtained by these methods were compared with those by Spin Echo pulse sequence. The results were as follows: 1. The optimal repetition times (TR) and echo times (TE) for T.M.J. image were; a. 400 msec and 18 msec in PMGR pulse sequence. b. 40 msec and 12 msec in GRASS pulse sequence. c. 700 msec and 30 msec in CSMEMP pulse sequence. d. 500 msec and 20 msec in Spin Echo pulse sequence. 2. When the MPGR pulse sequence was using, T2-weighted image was obtained in very short time. On the image of the paracoronal plane by GRASS pulse sequence, meniscus showed the moderate signal intensity, and the meniscus and its anteromedial, posterolateral attachments were observed definitely with gray color. 4. The signal intensity of Spin Echo pulse sequence was equal to that of CSMEMP pulse sequence, but the image by CSMEMP pulse sequence showed relatively lower level in its resolution.

• Progress in Superconductivity
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• v.10 no.1
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• pp.50-54
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• 2008

A conduction-cooled superconducting magnet system is developed for material separation. The superconducting magnet for material separation has to be designed to have a strong magnetic field in a control volume. Since the magnetic field gradient is larger at the end rather than at the center of the magnet, we developed a design method to optimize the superconducting magnet for material separation. The safety of the superconducting magnet is evaluated, taking into account the electro-magnetic field, heat and structure. The superconducting coil is successfully wound by the wet-winding method. The superconducting coil is installed in a cryostat maintaining high vacuum, and cooled down to approximately 4 K by a two-stage GM cryocooler. The performance of the conduction-cooled superconducting magnet system is discussed with respect to the supplied current, cooling medium and cooling power of a cryocooler.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.981-984
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• 2014

Volumetric measurement of hippocampus using IBASPM, the 20's normal adults 10 people's brain images were acquired in order to assess the changes according to the type of the Atlas. Images was obtained using MPRAGE of a 3-D gradient echo pulse sequence on Head matrix coil of 1.5T MRI system. The results of Paired t-test using obtained volume of hippocampus depending on the type of the Atlas, Atlas69-Altas84, Atlas69-Atlas116(p=0.729, 0.729) in the left hippocampus and Atlas69-Atlas84, Atlas69-Atlas116(p=0.219, 0.219) in right hippocampal formation were no significant differences but in the area except this, there was significant difference(p=0.000). The volume of the hippocampus using Atlas84 and Atlas116, represented the same value and there was no significant difference. In the image analysis using the overlay of atlas image and original image, Atlas71 could be found that the area of hippocampus did mismatch. In the case of atlas used in this study, because it has been developed by the westerners, there are differences between brain of asian. It would be needed to development of new Atlas for high accuracy measurement of the volume of hippocampus.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2171-2174
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• 2008

The design of thermal radiation shield cooled by a cryocooler is presented. This study is motivated mainly by our recent development of prototype superconducting magnet system for the Cyclotron K120. The superconducting magnet system is composed of the magnet cryostat, transfer line and supply cryostat. In order to minimize thermal radiation load, the superconducting coil form in the magnet cryostat is enclosed by the thermal radiation shield which is thermally connected to the first-stage cold head of a two-stage cryocooler in the supply cryostat. Since the supply cryostat is located far from the magnet cryostat large temperature gradient along the thermal shield is unavoidable. In this paper, the thermal radiation shield is optimized to minimize temperature gradient with taking into account the cryogenic load, system structure and electrical load. The effect of heat source from thermal conduction through mechanical supports on the temperature distribution of thermal radiation shield is also discussed.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.352-361
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• 2018

This paper proposes a sensing system of the Halbach array permanent magnet spherical motor(PMSM). The rotor position can be obtained by solving three rotation angles, which revolves around 3 reference axes of the stator. With the development of 3-D hall sensor, the position identification problem of the Halbach array PMSM based on rotor magnetic field is studied in this paper. A nonlinear and serious coupling relationship between the rotation angles and the measured magnetic flux density is established on the basis of the rotation transformation theory and the magnetic field model. In order to get rid of the influence on position detection caused by the harmonics of rotor magnetic field and the stator coil magnetic field, a sensor location combination scheme is proposed. In order to solve the nonlinear equation fast and accurately, a new position solution algorithm which combines the merits of gradient projection and particle swarm optimization(PSO) is presented. Then the rotation angles are obtained and the rotor position is identified. The validity of the sensing system is verified through the simulation.