• 대한의용생체공학회:의공학회지
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• 제17권4호
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• pp.525-534
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• 1996

We have developed a fast steady state free precession interferometry (SSFPI) technique which is useful for the fMRl (functional Magnetic Resonance Imaging). As is known, SSFP sequence with a suitable adjustment of Vadient (readeut) allows us to measure precession angle 6 which in tw relates to the field inhomogeneity. Combining the two pulses (known as FID and Echo) in FADE (Fast Acquisition Double Echo) sequence, for example, one can obtain the interference term which is directly related to the precession angle It has been known that a fast high resolution magnetic field mapping is possible by use of the modified FADE sequence or SSFPI, and we have attempted to use the SSFPI technique for the susceptibility-induced fMRl. When the method is applied to the susceptibility effect based functional magnetic resonance imaging (fMRl), it was found that the direct susceptibility effect measurement was possible without perturbations such as the backgrounds and inflow effect. In this paper, simulation results and experimental results obtained with 2.0 Tesla MRI system are presented.

• Journal of Electrical Engineering and Technology
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• 제12권5호
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• pp.1963-1969
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• 2017

In order to overcome the manufacturing difficulty of the transverse-flux permanent magnet linear motor (TFPMLM) and enhance its performance much better, a novel TFPMLM with E-core and 3 dimension (3D) magnetic structures is proposed in this paper. Firstly, its basic structure and operating principle are presented. Then the equivalent 2D configuration of the TFPMLM is transformed, so that the Schwarz-Christoffel (SC) mapping method can be used to analyze the motor. Furthermore, the air gap flux density distribution is solved by SC mapping method, based on which, the EMF waveform, no-load cogging force waveform and load force waveform are obtained. Finally, the prototyped TLPMLM is manufactured and the results are obtained from the experiment and 3D FEM, respectively, which are used to compare with those from SC mapping method.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 학술대회 논문집 정보 및 제어부문
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• pp.486-488
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• 2008

300 MHz가 넘는 초고자장 MRI에서는 송신 또는 수신 RF Magnetic Field 의 불균일도가 심해져서 이를 개선하기 위한 많은 방법들이 제안되고 있다. 그 중 가장 대표적인 방법은 $4{\sim}32$ 채널의 Transmit Array의 각 채널에 인가되는 전압과 위상을 변화시켜 RF Magnetic Field의 불균일도를 개선하는 방법이다. 본 논문에서는 Transmit Array 내부에서 머리위치의 변화에 따라 RF Magnetic Field ($B_1$ Field) 의 불균일도가 많이 변화하며 이에 따라 RF 송신용 전압과 위상의 Pattern을 새로 최적화 해야 함을 확인하였다. 또한 RF field Mapping을 하기 위해서 Composite RF Sequence를 사용한 Rapid Sequence의 사용과 채널 전압과 위상을 최적화하기 위해서 일반적인 Iterative 방식보다 간편하고 빠른 Target Method를 제안하였다. Driving 패턴의 최적화는 Complex 행렬식을 사용했으며 RF Magnetic Field ($B_1$ Field) 분포는 FDTD 방식으로 계산하였다.

• Investigative Magnetic Resonance Imaging
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• 제23권4호
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• pp.328-340
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• 2019

Purpose: To generate phase images with free of motion-induced artifact and susceptibility-induced distortion using 3D radial ultrashort TE (UTE) MRI. Materials and Methods: The field map was theoretically derived by solving Laplace's equation with appropriate boundary conditions, and used to simulate the image distortion in conventional spin-warp MRI. Manufacturer's 3D radial imaging sequence was modified to acquire maximum number of radial spokes in a given time, by removing the spoiler gradient and sampling during both rampup and rampdown gradient. Spoke direction randomly jumps so that a readout gradient acts as a spoiling gradient for the previous spoke. The custom raw data was reconstructed using a homemade image reconstruction software, which is programmed using Python language. The method was applied to a phantom and in-vivo human brain and abdomen. The performance of UTE was compared with 3D GRE for phase mapping. Local phase mapping was compared with T₂* mapping using UTE. Results: The phase map using UTE mimics true field-map, which was theoretically calculated, while that using 3D GRE revealed both motion-induced artifact and geometric distortion. Motion-free imaging is particularly crucial for application of phase mapping for abdomen MRI, which typically requires multiple breathold acquisitions. The air pockets, which are caught within the digestive pathway, induce spatially varying and large background field. T₂* map, that was calculated using UTE data, suffers from non-uniform T₂* value due to this background field, while does not appear in the local phase map of UTE data. Conclusion: Phase map generated using UTE mimicked the true field map even when non-zero susceptibility objects were present. Phase map generated by 3D GRE did not accurately mimic the true field map when non-zero susceptibility objects were present due to the significant field distortion as theoretically calculated. Nonetheless, UTE allows for phase maps to be free of susceptibility-induced distortion without the use of any post-processing protocols.

• 대한자기공명의과학회:학술대회논문집
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• 대한자기공명의과학회 2007년도 학술대회
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• pp.72-72
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• 2007

• 천문학회보
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• 제33권2호
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• pp.57.1-57.1
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• 2008

• 한국지능시스템학회논문지
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• 제15권1호
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• pp.75-80
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• 2005

이 논문에서는 지능형 교통시스템에서 자율주행용 자계도로 3차원적으로 해석하여 차량의 위치를 검출하기 위한 시스템에 관하여 다룬다. 특히 자율주행시스템을 구성하는 핵심요소 중 하나인 위치검출시스템의 새로운 방법을 제안한다. 기존의 위치검출시스템은 자계와 차량의 위치 관계를 맵핑하는 원리를 이용한다. 이는 데이터의 저장이 필수적이며 대용량의 메모리를 요구되어 상용화시 고비용의 문제점을 가지고 있다. 이 논문에서는 기존 위치검출시스템이 가지는 문제점을 극복하기 위한 방법으로 신경망을 이용한 위치검출시스템을 제안한다. 그리고 제안한 위치검출시스템을 적용한 자율주행시스템을 설계한다. 설계한 자율주행시스템의 적용 가능성을 파악하기 위하여 자율주행실험을 행하고 이를 분석한다.

• Investigative Magnetic Resonance Imaging
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• 제11권2호
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• pp.95-102
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• 2007

목적: 3.0 Tesla와 같은 고 자장에서 고해상도의 나선주사영상을 얻기 위해서는 주자장을 균일하게 만들어야 한다. 특히, 나선주사영상인 경우 스핀-에코펄스 시퀀스(SE)나 경사자계 에코 펄스 시퀀스(GE)에 비하여 측정 시간이 길기 때문에 주자장이 균일하지 못하다면, off-resonance 현상으로 영상의 blur가 심해진다. 본 연구에서는 빠른 시간 안에 주자장을 균일하게 할 수 있는 고차(Higher-order) shimming방법을 모색했다. 대상 및 방법: 3 Tesla 자기 공명 영상시스템에서 고해상도의 나선주사영상을 얻기에 적합할 정도의 균일한 주자장을 빠른 시간 안에 만들기 위해, 한번의 스캔으로 axial, sagittal, coronal 방향의 불균일도 map을 구할 수 있는 펄스 시퀀스를 제안하였고, 불균일도 map으로부터 spherical harmonics 분석를 통해 shim 코일에 적절한 전류를 인가하여 주자장을 균일하게 만들었다. 결과: 3 Tesla 자기 공명 영상 시스템에서 주자장의 불균일도는 주자장의 크기에 비례하게 된다. 제안한 펄스 시퀀스로 얻은 영상을 이용하여 불균일도 Map을 만들 수 있었고, 이를 spherical harmonics 분석을 하여 2-3회의 고차 shimming으로 불균일한 자장을 균일하게 만들 수 있었다. 제안된 고차 shimming 방법은 전체 영상 영역 뿐만 아니라 선택한 영역에 대해서만 적용도 가능하기 때문에 국부 영역에 대한 고차 shimming이 가능하다. 고차 shimming이 적용되어 주자장이 균일하게 개선된 상태에서 고해상도의 나선주사영상을 얻을 수 있었다. 결론: 3 Tesla 고자장 자기 공명 영상 시스템에서 주자장의 불균일도를 개선하기 위한 펄스 시퀀스와 알고리즘을 통해 주자장의 불균일도를 빠른 시간 안에 개선할 수 있었다. 주자장의 불균일도를 효과적으로 개선함으로써, 고해상도의 나선주사 영상을 얻을 수 있었다.

• Journal of Astronomy and Space Sciences
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• 제11권1호
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• pp.81-92
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• 1994

The magnetic field measurements from the KitSat-1 and KitSat-2 were tested by comparing with the IGRF model. The magnetic data have been collected by a three-axis fluxgate magnetometer on each satellite at an latitude of 1,325 km and 820 km, respectively. To avoid highly variable magnetic disturbances at the polar region, the field map has been within the limits of 50 degrees in latitude. Each data is averaged over the square of $5{\times}5$ degrees in both latitude and longitude. In these results, the relatively quiet periods were selected and the sampling rate was 30 seconds. It is shown that the results from these measurements are consistent with the IGRF map over the global surface map.

• Investigative Magnetic Resonance Imaging
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• 제22권1호
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• pp.37-49
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• 2018

Purpose: The effect of global inhomogeneity on quantitative susceptibility mapping (QSM) was investigated. A technique referred to as Simultaneous Unwrapping Phase with Error Recovery from inhomogeneity (SUPER) is suggested as a preprocessing to QSM to remove global field inhomogeneity-induced phase by polynomial fitting. Materials and Methods: The effect of global inhomogeneity on QSM was investigated by numerical simulations. Three types of global inhomogeneity were added to the tissue susceptibility phase, and the root mean square error (RMSE) in the susceptibility map was evaluated. In-vivo QSM imaging with volunteers was carried out for 3.0T and 7.0T MRI systems to demonstrate the efficacy of the proposed method. Results: The SUPER technique removed harmonic and non-harmonic global phases. Previously only the harmonic phase was removed by the background phase removal method. The global phase contained a non-harmonic phase due to various experimental and physiological causes, which degraded a susceptibility map. The RMSE in the susceptibility map increased under the influence of global inhomogeneity; while the error was consistent, irrespective of the global inhomogeneity, if the inhomogeneity was corrected by the SUPER technique. In-vivo QSM imaging with volunteers at 3.0T and 7.0T MRI systems showed better definition in small vascular structures and reduced fluctuation and non-uniformity in the frontal lobes, where field inhomogeneity was more severe. Conclusion: Correcting global inhomogeneity using the SUPER technique is an effective way to obtain an accurate susceptibility map on QSM method. Since the susceptibility variations are small quantities in the brain tissue, correction of the inhomogeneity is an essential element for obtaining an accurate QSM.