Improved three-dimensional multi-echo gradient echo based myelin water fraction mapping with phase related artifact correction

Lee, Hongpyo,Nam, Yoonho,Lee, Ho-Joon,Hsu, Jung-Jiin,Henry, Roland G.,Kim, Dong-Hyun Elsevier 2018 NeuroImage Vol.169 No.-

<P><B>Abstract</B></P> <P>Myelin water fraction (MWF) mapping with a multi-echo gradient echo (mGRE) sequence using complex-value based model fitting approach was recently described, in which the phase of the data plays an important role in the accuracy of the fitting results. Thus, influences coming from the undesirable phase components need to be reduced. Targeted for improved MWF mapping, methods to combat these phase related issues which include offset correction, main magnetic field (B<SUB>0</SUB>) inhomogeneity related correction, and flow compensation have been developed. For offset correction, a coil combine method with bipolar readout gradients has been devised. For B<SUB>0</SUB> related artifact, a voxel spread function correction approach along with a navigator echo acquisition was utilized. Finally, flow compensation gradients were used to reduce the effects of flow from regions including the veins. The correction methods led to reduced residual fitting error and improved quality of the resultant MWF maps. Quantitative analysis shows increased reliability when the corrections were used. Data from normal volunteers showed improved MWF mapping with the integrated method developed in this work.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We have explored a 3D MWF mapping method which accounts for phase related artifacts. </LI> <LI> Complex-valued modeling and complex three-compartment fitting show improved reliability when phase related disturbances are compensated. </LI> <LI> The results will improve the quality of mGRE based MWF mapping in human brain. </LI> </UL> </P>

Susceptibility Weighted Imaging of the Cervical Spinal Cord with Compensation of Respiratory-Induced Artifact

Lee, Hongpyo,Nam, Yoonho,Gho, Sung-Min,Han, Dongyeob,Kim, Eung Yeop,Lee, Sheen-Woo,Kim, Dong-Hyun Korean Society of Magnetic Resonance in Medicine 2018 Investigative Magnetic Resonance Imaging Vol.22 No.4

Purpose: The objective of this study was to obtain improved susceptibility weighted images (SWI) of the cervical spinal cord using respiratory-induced artifact compensation. Materials and Methods: The artifact from $B_0$ fluctuations by respiration could be compensated using a double navigator echo approach. The two navigators were inserted in an SWI sequence before and after the image readouts. The $B_0$ fluctuation was measured by each navigator echoes, and the inverse of the fluctuation was applied to eliminate the artifact from fluctuation. The degree of compensation was quantified using a quality index (QI) term for compensated imaging using each navigator. Also, the effect of compensation was analyzed according to the position of the spinal cord using QI values. Results: Compensation using navigator echo gave the improved visualization of SWI in cervical spinal cord compared to non-compensated images. Before compensation, images were influenced by artificial noise from motion in both the superior (QI = 0.031) and inferior (QI = 0.043) regions. In most parts of the superior regions, the second navigator resulted in better quality (QI = 0.024, P < 0.01) compared to the first navigator, but in the inferior regions the first navigator showed better quality (QI = 0.033, P < 0.01) after correction. Conclusion: Motion compensation using a double navigator method can increase the improvement of the SWI in the cervical spinal cord. The proposed method makes SWI a useful tool for the diagnosis of spinal cord injury by reducing respiratory-induced artifact.

Compact mobile handset MIMO antenna for LTE700 applications

Bae, Hongpyo,Harackiewicz, Frances J.,Park, Myun-Joo,Kim, Taekyun,Kim, Namhoon,Kim, Deokyun,Lee, Byungje Wiley Subscription Services, Inc., A Wiley Company 2010 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS Vol.52 No.11

<P>A compact mobile handset multiple-input multiple-output (MIMO) antenna for LTE700 applications is proposed.The proposed antenna consists of two side-to-side printed symmetrical printed inverted-F antennas (PIFAs), a capacitively coupled feed, a suspended line, and a branch line. A wide impedance bandwidth at relatively lower frequency is achieved with the capacitively coupled feed. Good isolation (>12 dB) and low correlation coefficient (< 0.1) between the MIMO antennas are obtained by adding the branch line in conjunction with the suspended line. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2419–2422, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25507</P>

Development of Drug Delivery System for Controlled Delivery Using Microfluidic Structures

Dasom Yang,Hongpyo Lee,WonHyoung Ryu 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.3

라이너 플레이트 및 콘크리트 공동을 고려한 원전 격납건물 벽체의 탄성파 전파 해석

김은영,김보영,강준원,이홍표,Kim, Eunyoung,Kim, Boyoung,Kang, Jun Won,Lee, Hongpyo 한국전산구조공학회 2021 한국전산구조공학회논문집 Vol.34 No.3

최근 국내 원자력발전소의 격납건물 벽체와 Containment Liner Plate(CLP) 사이에서 다양한 크기의 공극이 발견됨에 따라 원전 격납건물의 보수를 위해 내부 공극의 분포와 크기를 정밀하게 평가할 수 있는 진단기법의 개발이 요구되고 있다. 이에 따라 이 연구에서는 격납건물 벽체에서의 탄성파 전파거동을 계산하는 2차원 유한요소해석 기법을 제시한다. 격납건물 벽체를 기반으로 해석영역을 구성하고 경계면에서의 반사파를 제거하기 위해 수치적 파동흡수 경계층인 perfectly matched layer를 도입하였다. Galerkin 기반 혼합유한요소법을 이용해 2차원 유한영역에서 탄성파 파동방정식의 해를 구하여 충격하중에 대한 격납건물 벽체의 변위와 응력을 계산하였다. 제시한 수치적 기법을 이용하여 격납건물 콘크리트 벽체의 CLP 부착 유무와 공동의 위치 및 크기 변화에 따른 탄성파 전파거동을 살펴보았다. 이 연구의 결과는 원전 격납건물 내부의 공동을 진단하는 탄성파 전체파형 역해석 기법 개발에 활용될 수 있다. Recent investigation into the integrity of nuclear containment buildings has highlighted the importance of developing an elaborate diagnostic method to evaluate the distribution and size of cavities inside concrete walls. As part of developing such a method, this paper presents a finite element approach to modeling elastic waves propagating in the containment building walls of a nuclear power plant. We introduce a perfectly matched layer (PML) wave-absorbing boundary to limit the large-scale nuclear containment wall to the region of interest. The formulation results in a semi-discrete form with symmetric damping and stiffness matrices. The transient elastic wave equations for a mixed unsplit-field PML were solved for displacement and stresses in the time domain. Numerical results show that the sensitivity of displacement, velocity, acceleration, and stresses is large depending on the size and location of the cavity. The dynamic response of the wall slightly differs depending on the existence of the containment liner plate. The results of this study can be applied to a full-waveform inversion approach for characterizing cavities inside a containment wall.

원전 구조내진 성능평가용 인프라 구축 현황

양달훈(Yang, Dal-Hun),김석철(Kim, Seokchul),이영윤(Lee, Young-Yoon),이홍표(Lee, Hongpyo) 대한토목학회 2023 대한토목학회 학술대회 Vol.2023 No.10

Susceptibility Weighted Imaging of the Cervical Spinal Cord with Compensation of Respiratory-Induced Artifact

김동현,Yoonho Nam,Sung-Min Gho,Dongyeob Han,Eung Yeop Kim,Sheen-Woo Lee,Hongpyo Lee 대한자기공명의과학회 2018 Investigative Magnetic Resonance Imaging Vol.22 No.4

Purpose: The objective of this study was to obtain improved susceptibility weighted images (SWI) of the cervical spinal cord using respiratory-induced artifact compensation. Materials and Methods: The artifact from B0 fluctuations by respiration could be compensated using a double navigator echo approach. The two navigators were inserted in an SWI sequence before and after the image readouts. The B0 fluctuation was measured by each navigator echoes, and the inverse of the fluctuation was applied to eliminate the artifact from fluctuation. The degree of compensation was quantified using a quality index (QI) term for compensated imaging using each navigator. Also, the effect of compensation was analyzed according to the position of the spinal cord using QI values. Results: Compensation using navigator echo gave the improved visualization of SWI in cervical spinal cord compared to non-compensated images. Before compensation, images were influenced by artificial noise from motion in both the superior (QI = 0.031) and inferior (QI = 0.043) regions. In most parts of the superior regions, the second navigator resulted in better quality (QI = 0.024, P < 0.01) compared to the first navigator, but in the inferior regions the first navigator showed better quality (QI = 0.033, P < 0.01) after correction. Conclusion: Motion compensation using a double navigator method can increase the improvement of the SWI in the cervical spinal cord. The proposed method makes SWI a useful tool for the diagnosis of spinal cord injury by reducing respiratory-induced artifact.