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141 results on '"Chang, Kyung Won"'

2. A human brain atlas of chi-separation for normative iron and myelin distributions

Author

Min, Kyeongseon, Sohn, Beomseok, Kim, Woo Jung, Park, Chae Jung, Song, Soohwa, Shin, Dong Hoon, Chang, Kyung Won, Shin, Na-Young, Kim, Minjun, Shin, Hyeong-Geol, Lee, Phil Hyu, and Lee, Jongho

Subjects
Electrical Engineering and Systems Science - Image and Video Processing, Quantitative Biology - Neurons and Cognition
Abstract

Iron and myelin are primary susceptibility sources in the human brain. These substances are essential for healthy brain, and their abnormalities are often related to various neurological disorders. Recently, an advanced susceptibility mapping technique, which is referred to as chi-separation, has been proposed, successfully disentangling paramagnetic iron from diamagnetic myelin. This method opened a potential for generating high resolution iron and myelin maps in the brain. Utilizing this technique, this study constructs a normative chi-separation atlas from 106 healthy human brains. The resulting atlas provides detailed anatomical structures associated with the distributions of iron and myelin, clearly delineating subcortical nuclei, thalamic nuclei, and white matter fiber bundles. Additionally, susceptibility values in a number of regions of interest are reported along with age-dependent changes. This atlas may have direct applications such as localization of subcortical structures for deep brain stimulation or high-intensity focused ultrasound and also serve as a valuable resource for future research., Comment: 19 pages, 9 figures

Published
2023

10. Convection in porous media with dispersion

Author

Wen, Baole, Chang, Kyung Won, and Hesse, Marc A.

Subjects
Physics - Fluid Dynamics
Abstract

We investigate the effect of dispersion on convection in porous media by performing direct numerical simulations (DNS) in a two-dimensional Rayleigh-Darcy domain. Scaling analysis of the governing equations shows that the dynamics of this system are not only controlled by the classical Rayleigh-Darcy number based on molecular diffusion, $Ra_m$, and the domain aspect ratio, but also controlled by two other dimensionless parameters: the dispersive Rayleigh number $Ra_d = H/\alpha_t$ and the dispersivity ratio $r = \alpha_l/\alpha_t$, where $H$ is the domain height, $\alpha_t$ and $\alpha_l$ are the transverse and longitudinal dispersivities, respectively. For $\Delta = Ra_d/Ra_m > O(1)$, the influence from the mechanical dispersion is minor; for $\Delta \ll 1$, however, the flow pattern is controlled by $Ra_d$ while the convective flux is $F\sim Ra_m$ for large $Ra_m$, but with a prefactor that has a non-monotonic dependence on $Ra_d$. Our DNS results also show that the increase of mechanical dispersion, i.e. decreasing $Ra_d$, will coarsen the convective pattern by increasing the plume spacing. Moreover, the inherent anisotropy of mechanical dispersion breaks the columnar structure of the mega-plumes at large $Ra_m$, if $Ra_d < 5000$. This results in a fan-flow geometry that reduces the convective flux.

Published
2018
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16. A human brain atlas of χ‐separation for normative iron and myelin distributions.

Author

Min, Kyeongseon, Sohn, Beomseok, Kim, Woo Jung, Park, Chae Jung, Song, Soohwa, Shin, Dong Hoon, Chang, Kyung Won, Shin, Na‐Young, Kim, Minjun, Shin, Hyeong‐Geol, Lee, Phil Hyu, and Lee, Jongho

Subjects
DEEP brain stimulation, THALAMIC nuclei, WHITE matter (Nerve tissue), MYELIN, NEUROLOGICAL disorders
Abstract

Iron and myelin are primary susceptibility sources in the human brain. These substances are essential for a healthy brain, and their abnormalities are often related to various neurological disorders. Recently, an advanced susceptibility mapping technique, which is referred to as χ‐separation (pronounced as "chi"‐separation), has been proposed, successfully disentangling paramagnetic iron from diamagnetic myelin. This method provided a new opportunity for generating high‐resolution iron and myelin maps of the brain. Utilizing this technique, this study constructs a normative χ‐separation atlas from 106 healthy human brains. The resulting atlas provides detailed anatomical structures associated with the distributions of iron and myelin, clearly delineating subcortical nuclei, thalamic nuclei, and white matter fiber bundles. Additionally, susceptibility values in a number of regions of interest are reported along with age‐dependent changes. This atlas may have direct applications such as localization of subcortical structures for deep brain stimulation or high‐intensity focused ultrasound and also serve as a valuable resource for future research. [ABSTRACT FROM AUTHOR]

Published
2024
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40. Technical and operative factors affecting magnetic resonance imaging–guided focused ultrasound thalamotomy for essential tremor: experience from 250 treatments

Author

Kim, Myung Ji, primary, Park, So Hee, additional, Chang, Kyung Won, additional, Kim, Yuhee, additional, Gao, Jing, additional, Kovalevsky, Maya, additional, Rachmilevitch, Itay, additional, Zadicario, Eyal, additional, Chang, Won Seok, additional, Jung, Hyun Ho, additional, and Chang, Jin Woo, additional

Published
2021
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50. Multiple steady states in exchange flows across faults and the dissolution of CO2

Author

Woods, Andrew W, Hesse, Marc, Berkowitz, Rachel, Chang, Kyung Won, and Apollo - University of Cambridge Repository

Subjects
porous media, convection
Abstract

We develop a model of the steady exchange flows which may develop between two aquifers at different levels in the geological strata and across which there is an unstable density stratification, as a result of their connection through a series of fractures. We show that in general there are multiple steady exchange flows which can develop, depending on the initial conditions, and which may involve a net upwards or downwards volume flux. We also show that there is a family of equilibrium exchange flows with zero net volume flux, each characterised by a different interlayer flux of buoyancy. We present experiments which confirm our simplified model of the exchange flow. Such exchange flows may supply unsaturated water from a deep aquifer to drive dissolution of a structurally trapped pool of geologically stored $\text{CO}_{2}$, once the water in the aquifer containing the trapped pool of $\text{CO}_{2}$ has become saturated in $\text{CO}_{2}$, and hence relatively dense. Such exchange flows may also lead to cross-contamination of aquifer fluids, which may be of relevance in assessing risks of geological storage systems.

Published
2015

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