• 한국초전도ㆍ저온공학회논문지
• /
• 제14권1호
• /
• pp.44-47
• /
• 2012

The substantial improvement of the signal-to-noise ratio (SNR) can be achieved with small-size samples or low-field MRI system by high-temperature superconducting(HTS) RF coil. The typical HTS RF coil made of HTS thin film is expensive and is limited the coil geometry to planar surface coil. In this study, commercial Bi-2223 HTS tapes was used as RF coil for a 0.35T permanent MRI system. It has advantages of both much lower cost and easier fabrication over HTS thin film coil. SNR gain of the image obtained from the HTS RF coil over a conventional Cu RF coil at room temperature was about 2.4-fold and 1.9-fold using the spin echo pulse sequence and gradient echo pulse sequence respectively.

• Investigative Magnetic Resonance Imaging
• /
• 제1권1호
• /
• pp.75-78
• /
• 1997

인체의 하지 MR Angiography(MRA)를 위한 하지전용 dual birdcage RF 코일을 설계, 제작하였으며 Volunteer실험을 하여 그 유용성을 보였다. 제안된 코일은 인체의 하지 전체의 영상을 위한 코일로 허벅지로부터 종아리까지 전체를 두 번의 영상을 통해 cover하게 된다. 기존의 방식대로 한 개의 코일을 옮기며 두 번 촬영할 경우 코일을 도중에 옮기게 외어 다리를 움직일 수밖에 없어 두 set의 영상이 완전히 연결이 되지 않지만 제안된 코일의 경우 침대만 움직이게 되므로 이런 문제가 없게 된다. 제안된 코일의 성능은 Volunteer의 하지 MRI 및 MRA를 얻어 확인했으며 임상적으로 매우 유용한 것으로 확인되었다.

• 한국초전도저온공학회:학술대회논문집
• /
• 한국초전도저온공학회 2000년도 KIASC Conference 2000 / 2000년도 학술대회 논문집
• /
• pp.173-176
• /
• 2000

MRI magnet has generally multi-section coil configurations to generate highly homogeneous magnetic field. Each coil is bridged by a shunt resistor to protect the superconducting magnet during quench. In order to optimize the shunt resistor, self inductance of each coil and mutual inductances between coils should be determined beforehand. Therefore, we calculated the self and the mutual inductances of MRI magnet with OPERA program for electromagnetic analysis.

• 한국자기공명학회논문지
• /
• 제7권1호
• /
• pp.25-36
• /
• 2003

The performance of radio frequency (RF) coils, used in MRI units, is determined by the image uniformity and the signal-to-noise ratio (SNR). Birdcage and surface coils are commonly used. A birdcage coil provides a good image uniformity while a surface coil produces a high SNR. In this study, therefore, a staircase coil was designed from a standard version of a birdcage coil, with some structural changes to increase SNR while maintaining image uniformity. In phantom experiments, the improvement of the image to uniformity and the SNR increase of the staircase coil compared with the values for the birdcage coil were about 3.5% and 35%, respectively. In clinical experiment, the SNR increase of the staircase coil, compared with the value for the birdcage coil was about 40% in bone, muscle and blood-vessel tissues. These results show that the performance of the staircase coil was very improved over the standard birdcage coil in terms of SNR, and that image uniformity was maintained. Therefore, the staircase coil designed by this study should be useful in experimental and clinical l.5T MRI systems, and this coil offers an alternative method of quadrature detection.

• 대한의용생체공학회:학술대회논문집
• /
• 대한의용생체공학회 1996년도 추계학술대회
• /
• pp.161-164
• /
• 1996

An actively-shielded $r^{2}$-gradient coil has been developed for brain localized MRI or MRS. Spatial localization is very useful for spatial volume selection in MRI or MR Spectroscopy(MRS). The radial(or $R^{2}-$) gradient coil is useful in reducing the artifact or in improving the SNR by selecting the volume with less number of RF pulses. It is, however, difficult to implement the coil with a gradient intensity strong enough to use it for practical whole-body MRI system. For example, the smallest volume size for selection is just 6 cm in diameter with a 250 Ampere of current driving for a whole-body system (in case of 70-cm-diameter). In this study, an asymetric $r^{2}$-coil with a small diameter of 35 cm has been designed and implemented for brain localized MRI or MRS. An 8-rod high-pass-type birdcage RF coil has also been implemented. The coil set has been developed for 1.0 Tesla Medison MRI system and its performance has been verified experimentally.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2007년도 심포지엄 논문집 정보 및 제어부문
• /
• pp.61-63
• /
• 2007

In high field (> 3 T) MR imaging, the magnetic field inhomogeneity in the target object increases due to the nonuniform electro-magnetic characteristics and relatively high Larmor frequency. Especially in the body imaging, the effect causes more serious problems resulting in locally high SAR(Specific Absorption Ratio). In this paper, we propose an optimized parallel-transmission RF coil element structure and show the utility of the coil by FDTD simulations to overcome the unwanted effects. Three types of TX coil elements are tested to maximize the efficiency and their driving patterns(amplitude and phase) optimized to have adequate field homogeneity, proper SAR level, and sufficient field strength. For the proposed coil element of 25 cm ${\times}$ 8 cm loop structure with 12 channels for a 3.0 T body coil, the 73% field non-uniformity without optimization was reduced to about 26% after optimization of driving patterns. The experimental as well as simulation results show the utility of the proposed parallel driving scheme is clinically useful for (ultra) high field MRI.

• 대한자기공명의과학회:학술대회논문집
• /
• 대한자기공명의과학회 2001년도 제6차 학술대회 초록집
• /
• pp.149-149
• /
• 2001

목적： Birdcage coil보다 SNR이 높은 Surface coil을 이용하여 시각 자극에 대한 반응 정도의 차이를 보이고자 한다. 대상 및 방법： 연구 개발 중인 Magnum 3.0T로 영상을 얻었다. 실험 대상자는 정상인 지원자로 하였고, 10Hz로 깜박거리는 발광다이오드를 이용하여 시각 자극을 실행하였다. 일정 paradigm으로 얻어진 영상은 SPM으로 분석하였다.

• 대한자기공명의과학회:학술대회논문집
• /
• 대한자기공명의과학회 2001년도 제6차 학술대회 초록집
• /
• pp.143-143
• /
• 2001

목적： 현재 3.0T MRI system은 세계적으로 개발이 진행되고 있는 가운데, 3.0T에서 사용할 수 있는 RF coil의 개발이 시급한 상황이다. 1.0T 및 1.5T MRI 와는 달리 3.0T에서 사용할 수 있는 Body coil 및 그에 따른 High power RF amplifier 제작에 많은 제약이 있다. 작은 용량의 RF amplifier를 이용하여 신체의 부분을 촬영 하고자 한다면, Tx/Rx 가능한 coil을 이용하면 가능할 것이다. 이러한 이유로 본 연구에서는 Tx/Rx 가능한 Quadrature type C-spine RF coil을 설계, 제작하여 3.0T 고자장 자기공명 영상장치에서의 임상진단 활용범위를 확대하였다.

• 한국산학기술학회논문지
• /
• 제11권12호
• /
• pp.4891-4895
• /
• 2010

본 자기공명영상장치(MRI: Magnetic Resonance Imaging)의 구성 요소인 RF Coil의 성능은 영상의 신호대 잡음비(Signal to Noise Ratio)를 결정하는 장치이다. RF Coil의 성능은 민감도(Sensitivity)와 라디오주파수 필드 균질성(RF Field Uniformity)으로 나타내고, RF Coil에 의해 유기되는 라디오 주파수 자기장(B1 Field)의 세기는 RF Coil의 구조 및 배열에 따라 공간적으로 달라진다. MRI 신호의 크기는 RF Coil이 만들어내는 자기장의 세기에 의해 결정되기 때문에 RF Coil에 의해 형성되는 공간상의 B1 Field의 분포를 확인할 수 있어야 한다. 본 논문에서는 다채널 RF Coil 설계에 있어서 가장 기본이 되는 형태의 RF Coil 구조와 이의 B1 Field 분포를 Matlab을 이용하여 모의실험을 통해 확인 하였다. Matlab을 이용하여 계산된 기본 구조의 RF 코일이 형성하는 B1 Field 분포는 다채널 RF 코일 설계시 매우 유용하게 사용될 수 있을 것이다.

• 센서학회지
• /
• 제26권4호
• /
• pp.245-250
• /
• 2017

A novel method to implement a birdcage-type receiving coil sensor for use in a magnetic resonance imaging(MRI) system has been demonstrated employing a flexible printed circuit board (FPCB) fabrication technique. Unlike the conventional methods, the two-dimensional shape of the coil sensor is first implemented as a FPCB and then it is attached to the surface of a cylindrical supporting structure to implement the three-dimensional birdcage-type coil sensor. The proposed method is very effective to implement object-specific MRI coil sensors especially for small animal measurements in research and preclinical applications since the existing well-developed FPCB-based techniques can easily meet the requirements on accuracies and costs during coil implement process. The performances of the coil sensor verified through $^1H$ 1.5T MRI measurements for small animals and it showed excellent characteristics by providing a high spatial precision and a high signal-to-noise ratio.