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Advances in gradient echo myelin water imaging at 3T and 7T
Shin, Hyeong-Geol,Oh, Se-Hong,Fukunaga, Masaki,Nam, Yoonho,Lee, Doohee,Jung, Woojin,Jo, Minju,Ji, Sooyeon,Choi, Joon Yul,Lee, Jongho ACADEMIC PRESS 2019 NEUROIMAGE Vol.188 No.-
<P><B>Abstract</B></P> <P>Gradient echo myelin water imaging (GRE-MWI) is an MRI technique to measure myelin concentration and involves the analysis of signal decay characteristics of the multi-echo gradient echo data. The method provides a myelin water fraction as a quantitative biomarker for myelin. In this work, a new sequence and post-processing methods were proposed to generate high quality GRE-MWI images at 3T and 7T. In order to capture the rapidly decaying myelin water signals, a bipolar readout GRE sequence was designed with 'gradient pairing,' compensating for the eddy current effects. The flip angle dependency from the multi-compartmental T<SUB>1</SUB> effects was explored and avoided using a 2D multi-slice acquisition with a long TR. Additionally, the sequence was tested for the effects of inflow and magnetization transfer and demonstrated robustness to these error sources. Lastly, the temporal and spatial B<SUB>0</SUB> inhomogeneity effects were mitigated by using the B<SUB>0</SUB> navigator and field inhomogeneity corrections. Using the method, high-quality myelin water images were successfully generated for the <I>in-vivo</I> human brain at both field strengths. When the myelin water fraction at 3T and 7T were compared, they showed a good correlation (R<SUP>2</SUP> ≥ 0.88; p < 0.001) with a larger myelin water fraction at 7T. The proposed method also opens the possibility of high resolution (isotropic 1.5 mm resolution) myelin water mapping at 7T.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Proposed a sequence for high quality GRE-MWI maps at 3T and 7T. </LI> <LI> Developed gradient pairing for eddy current compensations. </LI> <LI> Optimized the sequence for physiological noise, flip angle, and MT effects. </LI> <LI> Achieved 1.5 mm isotropic resolution myelin water images at 7T. </LI> </UL> </P>
Dae Geol Jeong,Jae Min Cha,Dae Sung Kim,Ju Hyeong Kim,Hwa Jin Jeong,Jae Young Shin,Jun Hyeon Bae,Bong Ki Ryu,Hisayuki Suematsu,Kenta Tanaka 대한금속ㆍ재료학회 2017 대한금속·재료학회지 Vol.55 No.11
Nanoscale Sn-Bi-Ag compound powders were successfully synthesized using the pulsed wire discharge (PWD) method. In PWD, when a high current is passed through high-density metal wires, the wires explode because of resistance heating, forming fine particles or metal vapor. In this study, we used Sn-Bi and Ag wires in order to obtain three-component nanopowders. A high current was applied to the wires between the electrodes in a N<sub>2</sub> atmosphere. We discussed the results based on the K factor, which is the ratio of the charging energy of the capacitor to the vaporization energy of the wire. The three-component (Sn-Bi-Ag) nanoparticles were synthesized under a N<sub>2</sub> atmosphere at 4 and 6 kV. From the particle-size distribution curves, it was found that the mean particle diameter (D<sub>1</sub>) values of the Sn-Bi and Ag nanopowders were within the range of 16.32-42.37 nm under each condition. The melting point of the Sn-Bi-Ag nanoparticles was found to be within the range of 188.68-214.97 ℃, which is about 40 ℃ lower than that obtained from the phase diagram and computational thermodynamics of the Sn-Bi-Ag system. In this study, the nanopowders were obtained by subjecting the wires at extreme energies, to improve their solid solubility. (Received February 8, 2017; Accepted July 26, 2017)
An R<sub>2</sub>* model of white matter for fiber orientation and myelin concentration
Lee, Jingu,Shin, Hyeong-Geol,Jung, Woojin,Nam, Yoonho,Oh, Se-Hong,Lee, Jongho Elsevier 2017 NeuroImage Vol.162 No.-
<P><B>Abstract</B></P> <P>Myelin, which consists of lipid bilayers, is one of the major constituents of white matter in the brain and has been suggested as a primary source of magnetic susceptibility contrasts. In this study, a new R<SUB>2</SUB>* model that simultaneously explains the effects of fiber orientation and myelin concentration is proposed and tested. In addition, a new approach that produces R<SUB>2</SUB>* maps without the effects of myelin is suggested. Experimental results demonstrate that the model reveals a high goodness of fit for the R<SUB>2</SUB>* distribution of white matter compared to a model that explains either fiber orientation or myelin concentration. The proposed R<SUB>2</SUB>* map shows a relatively uniform spatial distribution of R<SUB>2</SUB>* compared to the uncorrected R<SUB>2</SUB>* map and the fiber orientation or myelin concentration corrected R<SUB>2</SUB>* map.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new R2* model for fiber orientation and myelin concentration is proposed. </LI> <LI> The model explains the total myelin effects on R2* in white matter. </LI> <LI> The myelin effects on R2* were subtracted to generate a new myelin-removed R2* map. </LI> <LI> The corrected R2* map reveals reduced R2* heterogeneity in white matter. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Lee, Jae Hyeong,Lee, Gil-Ho,Park, Joonbum,Lee, Janghee,Nam, Seung-Geol,Shin, Yun-Sok,Kim, Jun Sung,Lee, Hu-Jong American Chemical Society 2014 NANO LETTERS Vol.14 No.9
<P>We report a surface-dominant Josephson effect in superconductor–topological insulator–superconductor (S–TI–S) devices, where a Bi<SUB>1.5</SUB>Sb<SUB>0.5</SUB>Te<SUB>1.7</SUB>Se<SUB>1.3</SUB> (BSTS) crystal flake was adopted as an intervening TI between Al superconducting electrodes. We observed a Fraunhofer-type critical current modulation in a perpendicular magnetic field in an Al–TI–Al junction for both local and nonlocal current biasing. Fraunhofer-type modulation of the differential resistance was also observed in a neighboring Au–TI–Au normal junction when it was nonlocally biased by the Al–TI–Al junction. In all cases, the Fraunhofer-like signal was highly robust to the magnetic field up to the critical field of the Al electrodes, corresponding to the edge-stepped nonuniform supercurrent density arising from the top and rough side surfaces of the BSTS flake, which strongly suggests that the Josephson coupling in a TI is established through the surface conducting channels that are topologically protected.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-9/nl501481b/production/images/medium/nl-2014-01481b_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl501481b'>ACS Electronic Supporting Info</A></P>