Publications by authors named "Jongho Lee"

184 Publications

Diffusion Tensor Imaging and Neurite Orientation Dispersion and Density Imaging Assessment of Optic Pathway Function in Patients With Anterior Visual Pathway Compression.

J Neuroophthalmol 2021 Jul 13. Epub 2021 Jul 13.

Department of Radiology (KMK, SHC), Seoul National University Hospital, Jongno-gu, Republic of Korea; Department of Electrical and Computer Engineering (E-JC), Laboratory for Imaging Science and Technology, Seoul National University, Gwanak-gu, Republic of Korea; AIRS Medical (WJ), Seoul, Republic of Korea; Department of Electrical and Computer Engineering (JL), Laboratory for Imaging Science and Technology, INMC, IOER, Seoul National University, Gwanak-gu, Republic of Korea and Department of Neurosurgery (YHK), Seoul National University Hospital, Jongno-gu, Republic of Korea.

Background: In patients with sellar or parasellar tumors, it is crucial to evaluate visual field impairment in the preoperative stage and to predict visual field improvement after the surgery. The purpose of this study was to investigate the associations of diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI) parameters in the optic radiations with preoperative and postoperative visual field impairment.

Methods: This prospective study included 81 participants with sellar or parasellar tumors. Multishell diffusion imaging and a visual field impairment score (VFIS) were acquired before and after the surgery. The multishell diffusion-weighted imaging was acquired to measure the neurite density and neurite orientation dispersion, as well as the diffusivity. DTI parameters were fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity, and radial diffusivity (RD). NODDI provided intracellular volume fraction (Vic), the orientation dispersion index, and isotropic volume fraction (Viso). The associations of DTI and NODDI parameters in the optic radiations with VFIS were investigated, adjusting for age, tumor height, and symptom duration.

Results: Among 162 optic radiations, 117 were functionally impaired in the preoperative stage. FA and Vic had significant negative correlations, whereas MD and RD had significant positive correlations with the VFIS (all P < 0.001). In the preoperative stage, lower FA (P = 0.001; odds ratio = 0.750) and Vic (P = 0.003; OR = 0.827) and higher MD (P = 0.007; OR = 1.244) and RD (P < 0.001; OR = 1.361) were significantly associated with the presence of visual field impairment. For the degree of postoperative improvement, preoperative lower Vic (P = 0.034; OR = 0.910) and higher MD (P = 0.037; OR = 1.103) and RD (P = 0.047; OR = 1.090) were significantly associated with more postoperative improvement.

Conclusions: DTI and NODDI parameters in the optic radiations were correlated with VFIS and associated with preoperative visual field impairments and postoperative improvement. It may help in predicting visual field improvement after the surgery in patients with sellar or parasellar tumors.
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http://dx.doi.org/10.1097/WNO.0000000000001309DOI Listing
July 2021

χ-separation: Magnetic susceptibility source separation toward iron and myelin mapping in the brain.

Neuroimage 2021 Jul 6;240:118371. Epub 2021 Jul 6.

Laboratory for Imaging Science and Technology, Department of Electrical and Computer Engineering, Seoul National University, Seoul, Republic of Korea. Electronic address:

Obtaining a histological fingerprint from the in-vivo brain has been a long-standing target of magnetic resonance imaging (MRI). In particular, non-invasive imaging of iron and myelin, which are involved in normal brain functions and are histopathological hallmarks in neurodegenerative diseases, has practical utilities in neuroscience and medicine. Here, we propose a biophysical model that describes the individual contribution of paramagnetic (e.g., iron) and diamagnetic (e.g., myelin) susceptibility sources to the frequency shift and transverse relaxation of MRI signals. Using this model, we develop a method, χ-separation, that generates the voxel-wise distributions of the two sources. The method is validated using computer simulation and phantom experiments, and applied to ex-vivo and in-vivo brains. The results delineate the well-known histological features of iron and myelin in the specimen, healthy volunteers, and multiple sclerosis patients. This new technology may serve as a practical tool for exploring the microstructural information of the brain.
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http://dx.doi.org/10.1016/j.neuroimage.2021.118371DOI Listing
July 2021

Quad-contrast Imaging: Simultaneous Acquisition of Four Contrast-weighted Images (PD-weighted, T2-weighted, PD-FLAIR and T2-FLAIR images) with Synthetic T1-weighted Image, T1-and T2-Maps.

IEEE Trans Med Imaging 2021 Jun 30;PP. Epub 2021 Jun 30.

Magnetic resonance imaging (MRI) can provide multiple contrast-weighted images using different pulse sequences and protocols. However, a long acquisition time of the images is a major challenge. To address this limitation, a new pulse sequence referred to as quad-contrast imaging is presented. The quad-contrast sequence enables the simultaneous acquisition of four contrast-weighted images (proton density (PD)-weighted, T2-weighted, PD-fluid attenuated inversion recovery (FLAIR), and T2-FLAIR), and the synthesis of T1-weighted images and T1-and T2-maps in a single scan. The scan time is less than 6 min and is further reduced to 2 min 50 s using a deep learning-based parallel imaging reconstruction. The natively acquired quad contrasts demonstrate high quality images, comparable to those from the conventional scans. The deep learning-based reconstruction successfully reconstructed highly accelerated data (acceleration factor 6), reporting smaller normalized root mean squared errors (NRMSEs) and higher structural similarities (SSIMs) than those from conventional generalized autocalibrating partially parallel acquisitions (GRAPPA)-reconstruction (mean NRMSE of 4.36% vs. 10.54% and mean SSIM of 0.990 vs. 0.953). In particular, the FLAIR contrast is natively acquired and does not suffer from lesion-like artifacts at the boundary of tissue and cerebrospinal fluid, differentiating the proposed method from synthetic imaging methods. The quad-contrast imaging method may have the potentials to be used in a clinical routine as a rapid diagnostic tool.
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http://dx.doi.org/10.1109/TMI.2021.3093617DOI Listing
June 2021

Contrast-enhanced MRI T1 Mapping for Quantitative Evaluation of Putative Dynamic Glymphatic Activity in the Human Brain in Sleep-Wake States.

Radiology 2021 Jun 22:203784. Epub 2021 Jun 22.

From the Departments of Radiology (S.L., R.E.Y., S.H.C., J.Y.L., I.H., K.M.K., T.J.Y., J.H.K., C.H.S.) and Clinical Pharmacology and Therapeutics (K.Y.H.), Seoul National University Hospital, Seoul National University College of Medicine, 101 Daehangno, Jongno-gu, Seoul 03080, Republic of Korea; Center for Nanoparticle Research, Institute for Basic Science, Seoul, Republic of Korea (S.H.C.); School of Chemical and Biological Engineering (S.H.C.) and Department of Electrical and Computer Engineering (S.J., J.L.), Seoul National University, Seoul, Republic of Korea; and Department of Biomedical Engineering, Hankuk University of Foreign Studies, Yongin-si, Republic of Korea (S.H.O.).

Background Evaluation of the glymphatic system with intrathecal contrast material injection has limited clinical use. Purpose To investigate the feasibility of using serial intravenous contrast-enhanced T1 mapping in the quantitative evaluation of putative dynamic glymphatic activity in various brain regions and to demonstrate the effect of sleep on glymphatic activity in humans. Materials and Methods In this prospective study from May 2019 to February 2020, 25 healthy participants (mean age, 25 years ± 2 [standard deviation]; 15 men) underwent two cycles of MRI (day and night cycles). For each cycle, T1 maps were acquired at baseline and 0.5, 1, 1.5, 2, and 12 hours after intravenous contrast material injection. For the night cycle, participants had a normal night of sleep between 2 and 12 hours. The time () to reach the minimum T1 value (T1), the absolute difference between baseline T1 and T1 (peak ΔT1), and the slope between two measurements at 2 and 12 hours (slope) were determined from T1 value-time curves in cerebral gray matter (GM), cerebral white matter (WM), cerebellar GM, cerebellar WM, and putamen. Mixed-model analysis of variance (ANOVA), Friedman test, and repeated-measures ANOVA were used to assess the effect of sleep on slope and to compare and peak ΔT1 among different regions. Results The slope increased from the day to night cycles in cerebral GM, cerebellar GM, and putamen (geometric mean ratio [night/day] = 1.4 [95% CI: 1.2, 1.7], 1.3 [95% CI: 1.1, 1.4], and 2.4 [95% CI: 1.6, 3.6], respectively; = .001, < .001, and < .001, respectively). Median values were 0.5 hour in cerebral and cerebellar GM and putamen for both cycles. Cerebellar GM had the highest mean peak ΔT1, followed by cerebral GM and putamen in both day (159 msec ± 6, 99 msec ± 4, and 62 msec ± 5, respectively) and night (152 msec ± 6, 104 msec ± 6, and 58 msec ± 4, respectively) cycles. Conclusion Clearance of a gadolinium-based contrast agent was greater after sleep compared with daytime wakefulness. These results suggest that sleep was associated with greater glymphatic clearance compared with wakefulness. © RSNA, 2021 . See also the editorial by Anzai and Minoshima in this issue.
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http://dx.doi.org/10.1148/radiol.2021203784DOI Listing
June 2021

State-of-the-art management technologies of dissolved methane in anaerobically-treated low-strength wastewaters: A review.

Water Res 2021 Jul 19;200:117269. Epub 2021 May 19.

Department of Civil Engineering, University of British Columbia, Vancouver, British Columbia, Canada, V6T 1Z4. Electronic address:

The recent advancement in low temperature anaerobic processes shows a great promise for realizing low-energy-cost, sustainable mainstream wastewater treatment. However, the considerable loss of the dissolved methane from anaerobically-treated low-strength wastewater significantly compromises the energy potential of the anaerobic processes and poses an environmental risk. In this review, the promises and challenges of existing and emerging technologies for dissolved methane management are examined: its removal, recovery, and on-site reuse. It begins by describing the working principles of gas-stripping and biological oxidation for methane removal, membrane contactors and vacuum degassers for methane recovery, and on-site biological conversion of dissolved methane into electricity or value-added biochemicals as direct energy sources or energy-compensating substances. A comparative assessment of these technologies in the three categories is presented based on methane treating efficiency, energy-production potential, applicability, and scalability. Finally, current research needs and future perspectives are highlighted to advance the future development of an economically and technically sustainable methane-management technology.
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http://dx.doi.org/10.1016/j.watres.2021.117269DOI Listing
July 2021

Visuomotor control of intermittent circular tracking movements with visually guided orbits in 3D VR environment.

PLoS One 2021 27;16(5):e0251371. Epub 2021 May 27.

Department of Clinical Engineering, Komatsu University, Komatsu, Japan.

The analysis of visually guided tracking movements is important to the understanding of imitation exercises and movements carried out using the human visuomotor control system. In this study, we analyzed the characteristics of visuomotor control in the intermittent performance of circular tracking movements by applying a system that can differentiate between the conditions of invisible and visible orbits and visible and invisible target phases implemented in a 3D VR space. By applying visuomotor control based on velocity control, our study participants were able to track objects with visible orbits with a precision of approximately 1.25 times greater than they could track objects with invisible orbits. We confirmed that position information is an important parameter related to intermittent motion at low speeds (below 0.5 Hz) and that tracked target velocity information could be obtained more precisely than position information at speeds above 0.5 Hz. Our results revealed that the feedforward (FF) control corresponding to velocity was delayed under the visible-orbit condition at speeds over 0.5 Hz, suggesting that, in carrying out imitation exercises and movements, the use of visually presented 3D guides can interfere with exercise learning and, therefore, that the effects of their use should be carefully considered.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0251371PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8158929PMC
May 2021

Perspectives and design considerations of capillary-driven artificial trees for fast dewatering processes.

Authors:
Jongho Lee

Sci Rep 2021 Apr 21;11(1):8631. Epub 2021 Apr 21.

Department of Civil Engineering, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada.

Recent progresses on nanocapillary-driven water transport under metastable conditions have substantiated the potential of artificial trees for dewatering applications in a wide pressure range. This paper presents a comprehensive performance analysis of artificial trees encompassing the principle for negative capillary pressure generation; impacts of structural, compositional, and environmental conditions on dewatering performance; and design considerations. It begins by delineating functionalities of artificial trees for evaporation (leaves), conduction (xylem), and filtration (root) of water, in the analogy to natural trees. The analysis revealed that the magnitude of (negative) capillary pressure in the artificial leaves and xylem must be sufficiently large to overcome the osmotic pressure of feed at the root. The required magnitude can be reduced by increasing the osmotic pressure in the artificial xylem conduits, which reduces the risk of cavitation and subsequent blockage of water transport. However, a severe concentration polarization that can occur in long xylem conduits would negate such compensation effect of xylem osmotic pressure, leading to vapor pressure depression at the artificial leaves and therefore reduced dewatering rates. Enhanced Taylor dispersions by increasing xylem conduit diameters are found to alleviate the concentration polarization, allowing for water flux enhancement directly by increasing leaf-to-root membrane area ratio.
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http://dx.doi.org/10.1038/s41598-021-88006-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8060284PMC
April 2021

The Site of Airway Collapse in Sleep Apnea, Its Associations with Disease Severity and Obesity, and Implications for Mechanical Interventions.

Am J Respir Crit Care Med 2021 Jul;204(1):103-106

Chonnam National University Medical School and Chonnam National University Hospital Gwangju, South Korea.

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http://dx.doi.org/10.1164/rccm.202011-4266LEDOI Listing
July 2021

An implantable optogenetic stimulator wirelessly powered by flexible photovoltaics with near-infrared (NIR) light.

Biosens Bioelectron 2021 May 4;180:113139. Epub 2021 Mar 4.

School of Mechanical Engineering, Gwangju Institute of Science and Technology (GIST), 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 61005, Republic of Korea. Electronic address:

Optogenetics is a cutting-edge tool in neuroscience that employs light-sensitive proteins and controlled illumination for neuromodulation. Its main advantage is the ability to demonstrate causal relationships by manipulating the activity of specific neuronal populations and observing behavioral phenotypes. However, the tethering system used to deliver light to optogenetic tools can constrain both natural animal behaviors and experimental design. Here, we present an optically powered and controlled wireless optogenetic system using near-infrared (NIR) light for high transmittance through live tissues. In vivo optogenetic stimulations using this system induced whisker movement in channelrhodopsin-expressing mice, confirming the photovoltaics-generated electrical power was sufficient, and the remote controlling system operated successfully. The proposed optogenetic system provides improved optogenetic applications in freely moving animals.
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http://dx.doi.org/10.1016/j.bios.2021.113139DOI Listing
May 2021

Improvement in Self-Heating Characteristic by Utilizing Sapphire Substrate in Omega-Gate-Shaped Nanowire Field Effect Transistor for Wearable, Military, and Aerospace Application.

J Nanosci Nanotechnol 2021 05;21(5):3092-3098

Department of Materials Science and Engineering, Seoul National University, Seoul 08826, Republic of Korea.

In this study, we propose an omega-shaped-gate nanowire field effect transistor (ONWFET) with a silicon-on-sapphire (SOS) substrate. In order to investigate improvements in the self-heating characteristic with the use of a SOS substrate, the lattice temperature is examined using a Synopsys Sentaurus 3D Technology computer-aided design (TCAD) simulator with the results compared to those with a silicon-on-insulator (SOI) substrate. To validate the proposed structure with the SOS substrate, the locations of hot spots and heat dissipation paths (heat sinks) depending on the substrate materials are also analyzed. The electrical characteristics, specifically the on-current (), off-current (), and subthreshold swing (SS), were investigated as well. Hence, it is demonstrated here that incorporating a SOS substrate can improve both the self-heating characteristic and the SS at the same time. Therefore, enhanced logic devices are feasible if using an ONWFET with a SOS substrate. Examples include wearable devices and military and future aerospace applications achieved by the radiation-resistant material Al₂O₃ that has high thermal conductivity.
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http://dx.doi.org/10.1166/jnn.2021.19149DOI Listing
May 2021

Dynamic Modulation of a Learned Motor Skill for Its Recruitment.

Front Comput Neurosci 2020 23;14:457682. Epub 2020 Dec 23.

Department of Psychiatry & Behavioral Sciences, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan.

Humans learn motor skills (MSs) through practice and experience and may then retain them for recruitment, which is effective as a rapid response for novel contexts. For an MS to be recruited for novel contexts, its recruitment range must be extended. In addressing this issue, we hypothesized that an MS is dynamically modulated according to the feedback context to expand its recruitment range into novel contexts, which do not involve the learning of an MS. The following two sub-issues are considered. We previously demonstrated that the learned MS could be recruited in novel contexts through its modulation, which is driven by dynamically regulating the synergistic redundancy between muscles according to the feedback context. However, this modulation is trained in the dynamics under the MS learning context. Learning an MS in a specific condition naturally causes movement deviation from the desired state when the MS is executed in a novel context. We hypothesized that this deviation can be reduced with the additional modulation of an MS, which tunes the MS-produced muscle activities by using the feedback gain signals driven by the deviation from the desired state. Based on this hypothesis, we propose a feedback gain signal-driven tuning model of a learned MS for its robust recruitment. This model is based on the neurophysiological architecture in the cortico-basal ganglia circuit, in which an MS is plausibly retained as it was learned and is then recruited by tuning its muscle control signals according to the feedback context. In this study, through computational simulation, we show that the proposed model may be used to neurophysiologically describe the recruitment of a learned MS in novel contexts.
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http://dx.doi.org/10.3389/fncom.2020.457682DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7793756PMC
December 2020

Sustainably Powered, Multifunctional Flexible Feedback Implant by the Bifacial Design and Si Photovoltaics.

Adv Healthc Mater 2021 02 16;10(3):e2001480. Epub 2020 Nov 16.

School of Mechanical Engineering, Gwangju Institute of Science and Technology (GIST), 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 61005, Republic of Korea.

Advanced design and integration of functioning devices with secured power is of interest for many applications that require complicated, sophisticated, or multifunctional processes in confined environments such as in human bodies. Here, strategies for design and realization are introduced for multifunctional feedback implants with the bifacial design and silicon (Si) photovoltaics in flexible forms. The approaches provide efficient design spaces for flexible Si photovoltaics facing up for sustainable powering and multiple electronic components for feedback functions facing down for sensing, processing, and stimulating in human bodies. The computational and experimental results including in vivo assessments ensure feasibility of the approaches by demonstrating feedback multifunctions, power-harvesting in milliwatts, and mechanical compatibility for operations in live tissues. This work should useful for wide range of applications that require sustainable power and advanced multifunctions.
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http://dx.doi.org/10.1002/adhm.202001480DOI Listing
February 2021

Synthetic MRI: Technologies and Applications in Neuroradiology.

J Magn Reson Imaging 2020 Nov 13. Epub 2020 Nov 13.

Department of Radiology, Seoul National University Hospital, Seoul, Republic of Korea.

Synthetic MRI is a technique that synthesizes contrast-weighted images from multicontrast MRI data. There have been advances in synthetic MRI since the technique was introduced. Although a number of synthetic MRI methods have been developed for quantifying one or more relaxometric parameters and for generating multiple contrast-weighted images, this review focuses on several methods that quantify all three relaxometric parameters (T , T , and proton density) and produce multiple contrast-weighted images. Acquisition, quantification, and image synthesis techniques are discussed for each method. We discuss the image quality and diagnostic accuracy of synthetic MRI methods and their clinical applications in neuroradiology. Based on this analysis, we highlight areas that need to be addressed for synthetic MRI to be widely implemented in the clinic. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY STAGE: 1.
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http://dx.doi.org/10.1002/jmri.27440DOI Listing
November 2020

DeepResp: Deep learning solution for respiration-induced B fluctuation artifacts in multi-slice GRE.

Neuroimage 2021 01 7;224:117432. Epub 2020 Oct 7.

Laboratory for Imaging Science and Technology, Department of Electrical and Computer Engineering, Seoul National University, Seoul, South Korea. Electronic address:

Respiration-induced B fluctuation corrupts MRI images by inducing phase errors in k-space. A few approaches such as navigator have been proposed to correct for the artifacts at the expense of sequence modification. In this study, a new deep learning method, which is referred to as DeepResp, is proposed for reducing the respiration-artifacts in multi-slice gradient echo (GRE) images. DeepResp is designed to extract the respiration-induced phase errors from a complex image using deep neural networks. Then, the network-generated phase errors are applied to the k-space data, creating an artifact-corrected image. For network training, the computer-simulated images were generated using artifact-free images and respiration data. When evaluated, both simulated images and in-vivo images of two different breathing conditions (deep breathing and natural breathing) show improvements (simulation: normalized root-mean-square error (NRMSE) from 7.8 ± 5.2% to 1.3 ± 0.6%; structural similarity (SSIM) from 0.88 ± 0.08 to 0.99 ± 0.01; ghost-to-signal-ratio (GSR) from 7.9 ± 7.2% to 0.6 ± 0.6%; deep breathing: NRMSE from 13.9 ± 4.6% to 5.8 ± 1.4%; SSIM from 0.86 ± 0.03 to 0.95 ± 0.01; GSR 20.2 ± 10.2% to 5.7 ± 2.3%; natural breathing: NRMSE from 5.2 ± 3.3% to 4.0 ± 2.5%; SSIM from 0.94 ± 0.04 to 0.97 ± 0.02; GSR 5.7 ± 5.0% to 2.8 ± 1.1%). Our approach does not require any modification of the sequence or additional hardware, and may therefore find useful applications. Furthermore, the deep neural networks extract respiration-induced phase errors, which is more interpretable and reliable than results of end-to-end trained networks.
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http://dx.doi.org/10.1016/j.neuroimage.2020.117432DOI Listing
January 2021

Deep Reinforcement Learning Designed Shinnar-Le Roux RF Pulse Using Root-Flipping: DeepRF.

IEEE Trans Med Imaging 2020 12 30;39(12):4391-4400. Epub 2020 Nov 30.

A novel approach of applying deep reinforcement learning to an RF pulse design is introduced. This method, which is referred to as DeepRF, is designed to minimize the peak amplitude or, equivalently, minimize the pulse duration of a multiband refocusing pulse generated by the Shinar Le-Roux (SLR) algorithm. In the method, the root pattern of SLR polynomial, which determines the RF pulse shape, is optimized by iterative applications of deep reinforcement learning and greedy tree search. When tested for the designs of the multiband pulses with three and seven slices, DeepRF demonstrated improved performance compared to conventional methods, generating shorter duration RF pulses in shorter computational time. In the experiments, the RF pulse from DeepRF produced a slice profile similar to the minimum-phase SLR RF pulse and the profiles matched to that of the computer simulation. Our approach suggests a new way of designing an RF by applying a machine learning algorithm, demonstrating a "machine-designed" MRI sequence.
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http://dx.doi.org/10.1109/TMI.2020.3018508DOI Listing
December 2020

Multi-group analysis using generalized additive kernel canonical correlation analysis.

Sci Rep 2020 07 28;10(1):12624. Epub 2020 Jul 28.

Department of Statistics, Seoul National University, Seoul, Korea.

Multivariate analysis has been widely used and one of the popular multivariate analysis methods is canonical correlation analysis (CCA). CCA finds the linear combination in each group that maximizes the Pearson correlation. CCA has been extended to a kernel CCA for nonlinear relationships and generalized CCA that can consider more than two groups. We propose an extension of CCA that allows multi-group and nonlinear relationships in an additive fashion for a better interpretation, which we termed as Generalized Additive Kernel Canonical Correlation Analysis (GAKCCA). In addition to exploring multi-group relationship with nonlinear extension, GAKCCA can reveal contribution of variables in each group; which enables in-depth structural analysis. A simulation study shows that GAKCCA can distinguish a relationship between groups and whether they are correlated or not. We applied GAKCCA to real data on neurodevelopmental status, psychosocial factors, clinical problems as well as neurophysiological measures of individuals. As a result, it is shown that the neurophysiological domain has a statistically significant relationship with the neurodevelopmental domain and clinical domain, respectively, which was not revealed in the ordinary CCA.
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http://dx.doi.org/10.1038/s41598-020-69575-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7387565PMC
July 2020

Elucidating the Trade-off between Membrane Wetting Resistance and Water Vapor Flux in Membrane Distillation.

Environ Sci Technol 2020 08 6;54(16):10333-10341. Epub 2020 Aug 6.

Department of Civil Engineering, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.

Membrane distillation (MD) has been receiving considerable attention as a promising technology for desalinating industrial wastewaters. While hydrophobic membranes are essential for the process, increasing membrane surface hydrophobicity generally leads to the reduction of water vapor flux. In this study, we investigate the mechanisms responsible for this trade-off relation in MD. We prepared hydrophobic membranes with different degrees of wetting resistance through coating quartz fiber membranes with a series of alkylsilane molecules while preserving the fiber structures. A trade-off between wetting resistance and water vapor flux was observed in direct-contact MD experiments, with the least-wetting-resistant membrane exhibiting twice as high vapor flux as the most wetting-resistant membrane. Electrochemical impedance analysis, combined with fluorescence microscopy, elucidated that a lower wetting resistance (still water-repelling) allows deeper penetration of the liquid-air interfaces into the membrane, resulting in an increased interfacial area and therefore a larger evaporative vapor flux. Finally, we performed osmotic distillation experiments employing anodized alumina membranes that possess straight nanopores with different degrees of wetting resistance, observed no trade-off, and substantiated this proposed mechanism. Our study provides a guideline to tailor the membrane surface wettability to ensure stable MD operations while maximizing the water recovery rate.
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http://dx.doi.org/10.1021/acs.est.0c02547DOI Listing
August 2020

A geometric approach to separate the effects of magnetic susceptibility and chemical shift/exchange in a phantom with isotropic magnetic susceptibility.

Magn Reson Med 2021 01 8;85(1):281-289. Epub 2020 Jul 8.

Laboratory for Imaging Science and Technology, Department of Electrical and Computer Engineering, Seoul National University, Seoul, Republic of Korea.

Purpose: To separate the effects of magnetic susceptibility and chemical shift/exchange in a phantom with isotropic magnetic susceptibility, and to generate a chemical shift/exchange-corrected QSM result.

Methods: Magnetic susceptibility and chemical shift/exchange are the properties of a material. Both are known to induce the resonance frequency shift in MRI. In current QSM, the susceptibility is reconstructed from the frequency shift, ignoring the contribution of the chemical shift/exchange. In this work, a simple geometric approach, which averages the frequency shift maps from three orthogonal B directions to generate a chemical shift/exchange map, is developed using the fact that the average nullifies the (isotropic) susceptibility effects. The resulting chemical shift/exchange map is subtracted from the total frequency shift, producing a frequency shift map solely from susceptibility. Finally, this frequency shift map is reconstructed to a susceptibility map using a QSM algorithm. The proposed method is validated in numerical simulations and applied to phantom experiments with olive oil, bovine serum albumin, ferritin, and iron oxide solutions.

Results: Both simulations and experiments confirm that the method successfully separates the contributions of the susceptibility and chemical shift/exchange, reporting the susceptibility and chemical shift/exchange of olive oil (susceptibility: 0.62 ppm, chemical shift: -3.60 ppm), bovine serum albumin (susceptibility: -0.059 ppm, chemical shift: 0.008 ppm), ferritin (susceptibility: 0.125 ppm, chemical shift: -0.005 ppm), and iron oxide (susceptibility: 0.30 ppm, chemical shift: -0.039 ppm) solutions.

Conclusion: The proposed method successfully separates the susceptibility and chemical shift/exchange in phantoms with isotropic magnetic susceptibility.
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http://dx.doi.org/10.1002/mrm.28408DOI Listing
January 2021

Active photonic wireless power transfer into live tissues.

Proc Natl Acad Sci U S A 2020 07 6;117(29):16856-16863. Epub 2020 Jul 6.

School of Mechanical Engineering, Gwangju Institute of Science and Technology (GIST), 61005 Gwangju, Republic of Korea;

Recent advances in soft materials and mechanics activate development of many new types of electrical medical implants. Electronic implants that provide exceptional functions, however, usually require more electrical power, resulting in shorter period of usages although many approaches have been suggested to harvest electrical power in human bodies by resolving the issues related to power density, biocompatibility, tissue damage, and others. Here, we report an active photonic power transfer approach at the level of a full system to secure sustainable electrical power in human bodies. The active photonic power transfer system consists of a pair of the skin-attachable photon source patch and the photovoltaic device array integrated in a flexible medical implant. The skin-attachable patch actively emits photons that can penetrate through live tissues to be captured by the photovoltaic devices in a medical implant. The wireless power transfer system is very simple, e.g., active power transfer in direct current (DC) to DC without extra circuits, and can be used for implantable medical electronics regardless of weather, covering by clothes, in indoor or outdoor at day and night. We demonstrate feasibility of the approach by presenting thermal and mechanical compatibility with soft live tissues while generating enough electrical power in live bodies through animal experiments. We expect that the results enable long-term use of currently available implants in addition to accelerating emerging types of electrical implants that require higher power to provide diverse convenient diagnostic and therapeutic functions in human bodies.
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http://dx.doi.org/10.1073/pnas.2002201117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7382277PMC
July 2020

The Cerebro-Cerebellum as a Locus of Forward Model: A Review.

Front Syst Neurosci 2020 9;14:19. Epub 2020 Apr 9.

Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan.

This review surveys physiological, behavioral, and morphological evidence converging to the view of the cerebro-cerebellum as loci of internal forward models. The cerebro-cerebellum, the phylogenetically newest expansion in the cerebellum, receives convergent inputs from cortical, subcortical, and spinal sources, and is thought to perform the predictive computation for both motor control, motor learning, and cognitive functions. This predictive computation is known as an internal forward model. First, we elucidate the theoretical foundations of an internal forward model and its role in motor control and motor learning within the framework of the optimal feedback control model. Then, we discuss a neural mechanism that generates various patterns of outputs from the cerebro-cerebellum. Three lines of supporting evidence for the internal-forward-model hypothesis are presented in detail. First, we provide physiological evidence that the cerebellar outputs (activities of dentate nucleus cells) are predictive for the cerebellar inputs [activities of mossy fibers (MFs)]. Second, we provide behavioral evidence that a component of movement kinematics is predictive for target motion in control subjects but lags behind a target motion in patients with cerebellar ataxia. Third, we provide morphological evidence that the cerebellar cortex and the dentate nucleus receive separate MF projections, a prerequisite for optimal estimation. Finally, we speculate that the predictive computation in the cerebro-cerebellum could be deployed to not only motor control but also to non-motor, cognitive functions. This review concludes that the predictive computation of the internal forward model is the unifying algorithmic principle for understanding diverse functions played by the cerebro-cerebellum.
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http://dx.doi.org/10.3389/fnsys.2020.00019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7160920PMC
April 2020

Overview of quantitative susceptibility mapping using deep learning: Current status, challenges and opportunities.

NMR Biomed 2020 Mar 23:e4292. Epub 2020 Mar 23.

Laboratory for Imaging Science and Technology, Department of Electrical and Computer Engineering, Seoul National University, Seoul, South Korea.

Quantitative susceptibility mapping (QSM) has gained broad interest in the field by extracting bulk tissue magnetic susceptibility, predominantly determined by myelin, iron and calcium from magnetic resonance imaging (MRI) phase measurements in vivo. Thereby, QSM can reveal pathological changes of these key components in a variety of diseases. QSM requires multiple processing steps such as phase unwrapping, background field removal and field-to-source inversion. Current state-of-the-art techniques utilize iterative optimization procedures to solve the inversion and background field correction, which are computationally expensive and require a careful choice of regularization parameters. With the recent success of deep learning using convolutional neural networks for solving ill-posed reconstruction problems, the QSM community also adapted these techniques and demonstrated that the QSM processing steps can be solved by efficient feed forward multiplications not requiring either iterative optimization or the choice of regularization parameters. Here, we review the current status of deep learning-based approaches for processing QSM, highlighting limitations and potential pitfalls, and discuss the future directions the field may take to exploit the latest advances in deep learning for QSM.
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http://dx.doi.org/10.1002/nbm.4292DOI Listing
March 2020

Recovery of dissolved methane from anaerobically treated food waste leachate using solvent-based membrane contactor.

Water Res 2020 May 4;175:115693. Epub 2020 Mar 4.

Department of Civil Engineering, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada. Electronic address:

The difficulty of dissolved methane recovery remains a major hurdle for mainstream anaerobic wastewater treatment processes. We recently proposed solvent-based membrane contactor (SMC) for high (>90%) methane recovery over a wide temperature range and net-energy production. Here, we investigate the methane recovery efficacy of the SMC process by using an AnMBR effluent from treating food waste leachate. We observed almost identical methane transfer kinetics to the process employing foulant-free methane-saturated feed solutions, with >92% methane recoveries, showing that organic foulants have insignificant impacts on the methane transport in the SMC. We then performed two different membrane contactor experiments: direct-contact membrane-distillation (DCMD, with transmembrane water vapor flow) and SMC (no water vapor flow). From the negligible fouling observed in the SMC experiment, opposite to the DCMD, we elucidate that the absence of water vapor flow renders the SMC process intrinsically robust to membrane fouling. With the low fouling propensity of the SMC process under highly fouling environments, our study highlights the feasibility of SMC processes to enhance the energy production in mainstream anaerobic wastewater treatment processes.
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http://dx.doi.org/10.1016/j.watres.2020.115693DOI Listing
May 2020

Stem cell-loaded adhesive immiscible liquid for regeneration of myocardial infarction.

J Control Release 2020 05 17;321:602-615. Epub 2020 Mar 17.

Department of Chemical Engineering, Pohang University of Science and Tech​nology, Pohang 37673, Republic of Korea. Electronic address:

Myocardial infarction (MI) causes serious loss of cardiac muscle and dysfunction. To restore MI, exogenous stem cells should be efficiently delivered. However, due to severe physical and physiological cardiac environment, recent strategies have faced challenges, including low cell persistence, low integration, and delayed therapeutic effects. Herein, we proposed mesenchymal stem cell (MSC) therapeutic platform using adhesive protein-based immiscible condensed liquid system (APICLS) derived from bioengineered mussel adhesive protein (MAP). With high encapsulation efficiency and survival rate of encapsulated MSCs, APICLS was successfully grafted by intramyocardial injection and distributed throughout the scarred myocardium. Its underwater adhesiveness and biocompatibility fostered integration with damaged tissue, resulting in high cell persistence and maximized paracrine effects. Bioactive molecules released from APICLS with MSCs induced angiogenesis and cardioprotection, delayed cardiac remodeling, reduced fibrosis, and recovered contractive force. Thus, our proposed strategy represents an innovative approach for recovering infarcted cardiac tissues with damaged structural and contractive function.
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http://dx.doi.org/10.1016/j.jconrel.2020.02.047DOI Listing
May 2020

Capillary-driven desalination in a synthetic mangrove.

Sci Adv 2020 02 21;6(8):eaax5253. Epub 2020 Feb 21.

Department of Chemical and Environmental Engineering, Yale University, New Haven, CT 06520-8286, USA.

According to the cohesion-tension theory, mangrove trees desalinate salty water using highly negative pressure (or tension) that is generated by evaporative capillary forces in mangrove leaves. Here, we demonstrate a synthetic mangrove that mimics the main features of the natural mangrove: capillary pumping (leaves), stable water conduction in highly metastable states (stem), and membrane desalination (root). When using nanoporous membranes as leaves, the maximum osmotic pressures of saline feeds (10 to 30 bar) allowing pure water uptake precisely correspond to expected capillary pressures based on the Young-Laplace equation. Hydrogel-based leaves allow for stable operation and desalination of hypersaline solutions with osmotic pressures approaching 400 bar, fivefold greater than the pressure limits of conventional reverse osmosis. Our findings support the applicability of the cohesion-tension theory to desalination in mangroves, provide a new platform to study plant hydraulics, and create possibilities for engineered membrane separations using large, passively generated capillary pressures.
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http://dx.doi.org/10.1126/sciadv.aax5253DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7034996PMC
February 2020

Nonlinear dipole inversion (NDI) enables robust quantitative susceptibility mapping (QSM).

NMR Biomed 2020 12 20;33(12):e4271. Epub 2020 Feb 20.

Department of Radiology, A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts, USA.

High-quality Quantitative Susceptibility Mapping (QSM) with Nonlinear Dipole Inversion (NDI) is developed with pre-determined regularization while matching the image quality of state-of-the-art reconstruction techniques and avoiding over-smoothing that these techniques often suffer from. NDI is flexible enough to allow for reconstruction from an arbitrary number of head orientations and outperforms COSMOS even when using as few as 1-direction data. This is made possible by a nonlinear forward-model that uses the magnitude as an effective prior, for which we derived a simple gradient descent update rule. We synergistically combine this physics-model with a Variational Network (VN) to leverage the power of deep learning in the VaNDI algorithm. This technique adopts the simple gradient descent rule from NDI and learns the network parameters during training, hence requires no additional parameter tuning. Further, we evaluate NDI at 7 T using highly accelerated Wave-CAIPI acquisitions at 0.5 mm isotropic resolution and demonstrate high-quality QSM from as few as 2-direction data.
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http://dx.doi.org/10.1002/nbm.4271DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7528217PMC
December 2020

Exploring linearity of deep neural network trained QSM: QSMnet

Neuroimage 2020 05 7;211:116619. Epub 2020 Feb 7.

Laboratory for Imaging Science and Technology, Department of Electrical and Computer Engineering, Seoul National University, Seoul, South Korea. Electronic address:

Recently, deep neural network-powered quantitative susceptibility mapping (QSM), QSMnet, successfully performed ill-conditioned dipole inversion in QSM and generated high-quality susceptibility maps. In this paper, the network, which was trained by healthy volunteer data, is evaluated for hemorrhagic lesions that have substantially higher susceptibility than healthy tissues in order to test "linearity" of QSMnet for susceptibility. The results show that QSMnet underestimates susceptibility in hemorrhagic lesions, revealing degraded linearity of the network for the untrained susceptibility range. To overcome this limitation, a data augmentation method is proposed to generalize the network for a wider range of susceptibility. The newly trained network, which is referred to as QSMnet, is assessed in computer-simulated lesions with an extended susceptibility range (-1.4 ​ppm to +1.4 ​ppm) and also in twelve hemorrhagic patients. The simulation results demonstrate improved linearity of QSMnet over QSMnet (root mean square error of QSMnet: 0.04 ​ppm vs. QSMnet: 0.36 ​ppm). When applied to patient data, QSMnet maps show less noticeable artifacts to those of conventional QSM maps. Moreover, the susceptibility values of QSMnet in hemorrhagic lesions are better matched to those of the conventional QSM method than those of QSMnet when analyzed using linear regression (QSMnet: slope ​= ​1.05, intercept ​= ​-0.03, R ​= ​0.93; QSMnet: slope ​= ​0.68, intercept ​= ​0.06, R ​= ​0.86), consolidating improved linearity in QSMnet. This study demonstrates the importance of the trained data range in deep neural network-powered parametric mapping and suggests the data augmentation approach for generalization of network. The new network can be applicable for a wide range of susceptibility quantification.
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http://dx.doi.org/10.1016/j.neuroimage.2020.116619DOI Listing
May 2020

So You Want to Image Myelin Using MRI: An Overview and Practical Guide for Myelin Water Imaging.

J Magn Reson Imaging 2021 02 3;53(2):360-373. Epub 2020 Feb 3.

Division of Biomedical Engineering, Hankuk University of Foreign Studies, Gyeonggi-do, Korea.

Myelin water imaging (MWI) is an MRI imaging biomarker for myelin. This method can generate an in vivo whole-brain myelin water fraction map in approximately 10 minutes. It has been applied in various applications including neurodegenerative disease, neurodevelopmental, and neuroplasticity studies. In this review we start with a brief introduction of myelin biology and discuss the contributions of myelin in conventional MRI contrasts. Then the MRI properties of myelin water and four different MWI methods, which are categorized as T -, T *-, T -, and steady-state-based MWI, are summarized. After that, we cover more practical issues such as availability, interpretation, and validation of these methods. To illustrate the utility of MWI as a clinical research tool, MWI studies for two diseases, multiple sclerosis and neuromyelitis optica, are introduced. Additional topics about imaging myelin in gray matter and non-MWI methods for myelin imaging are also included. Although technical and physiological limitations exist, MWI is a potent surrogate biomarker of myelin that carries valuable and useful information of myelin. Evidence Level: 5 Technical Efficacy: 1 J. MAGN. RESON. IMAGING 2021;53:360-373.
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http://dx.doi.org/10.1002/jmri.27059DOI Listing
February 2021

Boron Nitride as a Passivation Capping Layer for AlGaN/GaN High Electron Mobility Transistors.

J Nanosci Nanotechnol 2020 Jul;20(7):4450-4453

Nano-Photonics Convergence Technology Group, Korea Institute of Industrial Technology, Gwangju 61012, South Korea.

We report on the electrical characteristics of AlGaN/GaN high-electron mobility transistors (HEMTs) with hexagonal boron nitride (h-BN) as a passivation capping layer. The HEMTs with h-BN layers showed an increase in current drainage and 103-times reduction in the gate-leakage current compared with those of conventional unpassivated HEMTs. Moreover, the extrinsic transconductance and the pulse responses were improved due to the reduced charge-trapping effect at the surface of HEMTs. From our observations, the h-BN can be used as a passivation capping layer for high-power electronic devices.
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http://dx.doi.org/10.1166/jnn.2020.17587DOI Listing
July 2020

The relationship between miRNA-26b and connective tissue growth factor in rat models of aortic banding and debanding.

Korean J Intern Med 2021 05 30;36(3):596-607. Epub 2019 Dec 30.

Division of Cardiology, Department of Internal Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea.

Background/aims: Connective tissue growth factor (CTGF) is a profibrotic factor implicated in pressure overload-mediated myocardial fibrosis. In this study, we determined the role of predicted CTGF-targeting microRNAs (miRNAs) in rat models of aortic stenosis and reverse cardiac remodeling.

Methods: Minimally invasive ascending aortic banding was performed in 24 7-week-old male Sprague-Dawley rats, which were divided into three groups. The banding group consisted of eight rats that were sacrificed immediately after 6 weeks of aortic constriction. The debanding group underwent aortic constriction for 4 weeks and was sacrificed 2 weeks after band removal. The third group underwent sham surgery. We investigated the expression of CTGF, transforming growth factor-β1 (TGFβ1), and matrix metalloproteinase-2 using ELISA and examined miRNA-26b, miRNA-133a, and miRNA-19b as predicted CTGF-targeting miRNAs based on miRNA databases in 24-hour TGFβ-stimulated and TGFβ- washed fibroblasts and myocardial tissues from all subjects.

Results: CTGF was elevated in 24-hour TGFβ-stimulated fibroblasts and decreased in 24-hour TGFβ-washed fibroblasts. miRNA-26b was significantly increased in TGFβ-washed fibroblasts compared with control and TGFβ-stimulated fibroblasts (p < 0.05). CTGF expression was significantly higher in the banding group than that in the sham and debanding groups. The relative expression levels of miRNA-26b were higher in the debanding group than in the banding group.

Conclusion: The results of our study using models of aortic banding and debanding suggested that miRNA-26b was significantly increased after aortic debanding. The in vitro model yielded the same results: miRNA-26b was upregulated after removal of TGFβ from fibroblasts.
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http://dx.doi.org/10.3904/kjim.2019.120DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8137408PMC
May 2021

Characteristic of Motor Control in Three-Dimensional Circular Tracking Movements during Monocular Vision.

Biomed Res Int 2019 3;2019:3867138. Epub 2019 Nov 3.

Department of Clinical Engineering, Komatsu University, Komatsu 923-8511, Japan.

Analysis of visually guided tracking movements is an important component of understanding human visuomotor control system. The aim of our study was to investigate the effects of different target speeds and different circular tracking planes, which provide different visual feedback of depth information, on temporal and spatial tracking accuracy. In this study, we analyze motor control characteristic of circular tracking movements during monocular vision in three-dimensional space using a virtual reality system. Three parameters in polar coordinates were analyzed: Δ, the difference in the distance from the fixed pole; Δ, the difference in the position angle; and Δ, the difference in the angular velocity. We compare the accuracy of visually guided circular tracking movements during monocular vision in two conditions: (1) movement in the frontal plane relative to the subject that requires less depth information and (2) movement in the sagittal plane relative to the subject that requires more depth information. We also examine differences in motor control at four different target speeds. The results show that depth information affects both spatial and temporal accuracy of circular tracking movement, whereas target speed only affects temporal accuracy of circular tracking movement. This suggests that different strategies of feedforward and feedback controls are performed in the tracking of movements.
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http://dx.doi.org/10.1155/2019/3867138DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6878803PMC
April 2020