• Title, Summary, Keyword: High-Field MRI

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Review of Recent Advancement of Ultra High Field Magnetic Resonance Imaging: from Anatomy to Tractography

  • Cho, Zang-Hee
    • Investigative Magnetic Resonance Imaging
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    • v.20 no.3
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    • pp.141-151
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    • 2016
  • Purpose: Advances of magnetic resonance imaging (MRI), especially that of the Ultra-High Field (UHF) MRI will be reviewed. Materials and Methods: Diffusion MRI data was obtained from a healthy adult young male of age 30 using a 7.0T research MRI scanner (Magnetom, Siemens) with 40 mT/m maximum gradient field. The specific imaging parameters used for the data acquisition were a single shot DW echo planar imaging. Results: Three areas of the imaging experiments are focused on for the study, namely the anatomy, angiography, and tractography. Conclusion: It is envisioned that, in near future, there will be more 7.0T MRIs for brain research and explosive clinical application research will also be developed, for example in the area of connectomics in neuroscience and clinical neurology and neurosurgery.

Comparison and Optimization of Parallel-Transmission RF Coil Elements for 3.0 T Body MRI (3.0 T MRI를 위한 Parallel-Transmission RF 코일 구조의 비교와 최적화)

  • Oh, Chang-Hyun;Lee, Heung-K.;Ryu, Yeun-Chul;Hyun, Jung-Ho;Choi, Hyuk-Jin
    • Proceedings of the KIEE Conference
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    • pp.61-63
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    • 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.

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B1+ Homogenizaion over Whole Field of View in High Field MRI (고자장 MRI에서의 영상 영역에 대한 B1+ 균질성)

  • Kim, Hong-Joon;Son, Hyeok-Woo;Cho, Young-Ki;Yoo, Hyoung-Suk
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.23 no.1
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    • pp.96-100
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    • 2012
  • In high static field magnetic resonance imaging(MRI) systems, $B_0$ fields of 7 T and 9.4 T, the impressed RF field shows larger inhomogeneity than in clinical MRI systems with B0 fields of 1.5 T and 3.0 T. In multi-channel RF coils, the magnitude and phase of the input to each coil element can be controlled independently to reduce the non-uniformity of the impressed RF $B_1^+$ field. The convex optimization technique has been used to obtain the optimum excitation parameters with iterative solutions for homogeneity in a selected ROI(Region of Interest). To demonstrate the technique, the multichannel transmission line coil was modeled together with a human head phantom at 400 MHz for the 9.4 T MRI system and $B_1^+$ fields are obtained. In this paper, all the optimized $B_1^+$ in each isolated ROIs are combined to achieve significantly improved homogeneity over the entire field of view. The simulation results for 9.4 T MRI systems are discussed in detail.

Fundamental Background for 3T MRI/MRS

  • Choe, Bo-Young
    • Proceedings of the KSMRM Conference
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    • pp.47-49
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    • 2002
  • At present, the trend of magnetic field strength in MRI system is dramatically changing. In early 70, the only low field (<0.5T) was developed. It was technically difficult to develop the high field system. At that time, people believed that the fine MR imaging could not be obtained in the high field MR system due to the magnetic susceptibility effect. However, 1.5T system was evolved at the end of 80, and used for clinical usage. Thus, it was proved that the signal to noise ratio (SNR) could be greatly contribute to enhance the image quality. And, the results of functional MRI and MR spectroscopy could be improved in the higher field MR system. So, 8T system was eventually developed in Ohio State University Hospital at the end of 90. Therefore, there is no doubt that the system with the ultra high magnetic field strength will be developed near future in 21 century.

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RF Field Inhomogeneity Changes Depending on the Head Position in Parallel-Transmission Ultra-High-Field MRI (초고자장 병렬송신 MRI에서의 머리위치에 따른 RF 필드의 불균일도 비교)

  • Oh, J.S.;Hyun, J.H.;Seo, J.H.;Oh, C.H.
    • Proceedings of the KIEE Conference
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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.

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Comparison and Optimization of Parallel-Transmission RF Coil Elements for 3.0 T Body MRI (3.0 T MRI를 위한 병렬전송 고주파 코일 구조 비교와 최적화)

  • Oh, Chang-Hyun;Lee, Heung-K.;Ryu, Yeun-Chul;Hyun, Jung-Ho;Choi, Hyuk-Jin
    • Journal of the Institute of Electronics Engineers of Korea SC
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    • v.44 no.4
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    • pp.55-60
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    • 2007
  • In high field (> 3 T) MR imaging, the magnetic field inhomogeneity in the target object increases due to the nonuniform electro-magnetic characteristics of the relatively high RF 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 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 $25cm{\times}8cm$ loop structure with 12 channels for a 3.0 T body coil, the field non-uniformity of more than 70% without optimization was reduced to about 26 % after the optimization of driving patterns. The experimental as well as simulation results show that the proposed parallel driving scheme is clinically useful for (ultra) high field MRI.

RF Shimming Considering Coupling Effects for High-Field MRI

  • Heo, Hye-Young;Cho, Min-Hyoung;Lee, Soo-Yeol
    • Journal of Biomedical Engineering Research
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    • v.29 no.4
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    • pp.267-271
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    • 2008
  • The RF shimming technique has been used to improve the transmit RF field homogeneity in highfield MRI. In the RF shimming technique, the amplitude and phase of the driving currents in each coil element are optimized to get homogenous flip angle or uniform image intensity. The inductive and capacitive coupling between the coil elements may degrade the RF field homogeneity if not taken into account in the optimization procedure. In this paper, we have analyzed the coupling effects on the RF shimming using a sixteen-element TEM RF coil model operating at 300 MHz. We have found that the coupling effects on the RF shimming can be reduced by putting high dielectric material between the active rung and the shield.

EM Algorithm-based Segmentation of Magnetic Resonance Image Corrupted by Bias Field (바이어스필드에 의해 왜곡된 MRI 영상자료분할을 위한 EM 알고리즘 기반 접근법)

  • 김승구
    • The Korean Journal of Applied Statistics
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    • v.16 no.2
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    • pp.305-319
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    • 2003
  • This paper provides a non-Bayesian method based on the expanded EM algorithm for segmenting the magnetic resonance images degraded by bias field. For the images with the intensity as a pixel value, many segmentation methods often fail to segment it because of the bias field(with low frequency) as well as noise(with high frequency). Our contextual approach is appropriately designed by using normal mixture model incorporated with Markov random field for noise-corrective segmentation and by using the penalized likelihood to estimate bias field for efficient bias filed-correction.

High-temperature superconductors for NMR/MRI magnets:opportunities and challenges

  • Iwasa, Yukikazu;Bascunan, Juan;Hahn, Seungyong;Yao, Weijun
    • Superconductivity and Cryogenics
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    • v.11 no.2
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    • pp.23-29
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    • 2009
  • The unique features of HTS offer opportunities and challenges to a number of applications. In this paper we focus on NMR and MRI magnets, illustrating them with the NMR/MRI magnets that we are currently and will shortly be engaged: a 1.3 GHz NMR magnet, an "annulus" magnet, and an $MgB_2$whole-body MRI magnet. The opportunities with HTS include: 1) high fields (e.g., 1.3 GHz magnet); 2) compactness (annulus magnet); and 3) enhanced stability despite liquid-helium-free operation ($MgB_2$whole-body MRI magnet). The challenges include: 1) a large screening current field detrimental to spatial field homogeneity (e.g., 1.3 GHz magnet); 2) uniformity of critical current density (annulus magnet); and 3) superconducting joints ($MgB_2$magnet).

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Clinical Applications of Breast MRI (유방자기공명영상의 임상 적용)

  • Cho, Nariya;Moon, Woo-Kyung
    • Investigative Magnetic Resonance Imaging
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    • v.13 no.1
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    • pp.1-8
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    • 2009
  • Breast MRI is a cutting-edge technology in the diagnosis and intervention of breast abnormalities. Over the last decade, breast MRI has evolved from a research field to a clinical field. Radiologists should understand the indications, how to obtain adequate images, and how to interpret and report their findings. Breast MRI is now used in the differentiation of benign from malignant mass, preoperative staging of breast cancer patients, assessment of tumor response to neoadjuvant chemotherapy, and evaluation of women with breast implants. It can also be used as a supplemental screening modality for high-risk women. Qualified radiologists and adequate MRI technique are crucial for the success of these purposes. This review is focused on the indication, standardized use of lexicon and categorization of breast MRI.

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