Taewon Choi

Seoul National University Bundang Hospital

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Co-Authors

Jinhyoung Park

Sungkyunkwan University

Byoungho Lee

Seoul National University

Minseok Koo

Sungkyunkwan University

Jae Seung Bang

Seoul National University Bundang Hospital

Si Un Lee

Seoul National University Bundang Hospital

Hyoung Soo Byoun

Chungnam National University

Chang Wan Oh

Seoul National University Bundang Hospital

O-Ki Kwon

Seoul National University Bundang Hospital

Seung Pil Ban

National University College

Yoonchan Jeong

Seoul National University

Cooperative Institutions

Seoul National University

Sungkyunkwan University

Samsung (South Korea)

Seoul National University Bundang Hospital

Electronics and Telecommunications Research Institute

New Generation University College

Yonsei University

National University College

Seoul National University Hospital

Kyung Hee University

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Two‐Dimensional Angular Bandwidth Broadening of Metasurface Grating

Advanced Photonics Research (2022)

Chulsoo Choi Taewon Choi Jeong-Geun Yun Chanhyung Yoo Byoungho Lee

Waveguide‐type near‐eye displays (NED) have attracted increasing attention in the market of augmented reality (AR) and virtual reality (VR) devices, thanks to their outstanding performance within ultra‐compact size. The performance of waveguide‐type NED mainly depends on the waveguide coupler that transmits the incident image to the user's eye through the total internal reflection (TIR) inside the waveguide. However, the waveguide couplers, that have been widely used, exhibit nonuniform diffraction efficiency within the transferable angular range, i.e., field of view (FoV) of waveguide‐type NED, so that the image intensity distribution distortion is induced. Thus, it is needed that many researchers focus on broadening angular bandwidth to overcome the non‐uniformity of the diffraction efficiency. Herein, the 2D angular bandwidth broadening metasurface grating that exhibits uniform and high diffraction efficiency for the 2D FoV range is proposed. Specifically, the proposed device is designed specifically, and the diffraction efficiency of this device shows uniform efficiency of about 75% with a variance of 0.25% for the FoV range, and it is demonstrated both numerically and experimentally. Consequently, it is expected that the proposed device can be a game‐changer in the market for waveguide‐type NED for the enhancement of image uniformity.

Waveguide

Diffraction efficiency

10.1002/adpr.202200158

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Citations (7)

Therapeutic Quadrisected Annular Array for Improving Magnetic Resonance Compatibility

IEEE Transactions on Biomedical Engineering (2021)

Seoyun Chang Hyun-Kyung Na Minseok Koo Taewon Choi Young-Hoon Kim

Focused ultrasound has been applied in brain therapeutics. Although focusing ultrasonic beams on multiple arbitrary regions under the guidance of magnetic resonance imaging(MRI) is needed for precise treatments, current therapeutic transducers with large pitch sizes have been optimized to focus on deep brain regions. While annular arrays can adjust the beam foci from cortical to deep regions, their circular shape may generate eddy current-induced magnetic flux during MRI. In this study, a quadrisected annular array is proposed to address these limitations.Conventional and quadrisected annular arrays with three elements were implemented by loading the electrode patterns onto an 850 kHz 1-3 composite PZT disc, with a diameter of 31 mm, including three rings. MR compatibilities were demonstrated by imaging an MRI phantom with pulse sequences for B0 and B1 mapping and spin-echo imaging. Acoustic beam profiles, with and without a macaque monkey skull, were measured. A quadrisected transducer was also used to open the blood-brain barrier(BBB).The flip angle distortion improved by 20% in spin-echo MR imaging. The acoustic beam distortions shifting the focal point from 36 to 41mm and elongating the focal zone from 10 to 15 mm could be recovered to nearly the original values. BBB openings in the hippocampus and basal region were also demonstrated.The MR compatibility was improved by the increased resistance of the electrodes in the quadrisected array maintaining dynamic focusing capabilities.The quadrisected annular design can be a fundamental structure for a larger MR-compatible segmented array transducer generating multiple acoustic foci.

Focal point

10.1109/tbme.2021.3090986

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Citations (2)

A Soft Housing Needle Ultrasonic Transducer for Focal Stimulation to Small Animal Brain

Annals of Biomedical Engineering (2019)

Taewon Choi Sungjun Bae Minah Suh Jinhyoung Park

Pulse repetition frequency

10.1007/s10439-019-02431-w

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Citations (15)

Development of Heating and Cooling System with New Heat Exchange Cycle for High Efficiency and Peak Power Reduction Using Real time Constant Refrigerant Pressure Control

Journal of the Korean Institute of Illuminating and Electrical Installation Engineers (2015)

Sun-Young Choi Young-Kug Lee Myeong-Gwang Choi Taewon Choi

Systemic heating and cooling air conditioning systems are popular in various industrial fields and even home. Recently, the rate of supply of this kind of multi-heat pump has been increased under ESCO financing supporting system. Generally the heat pumping system has a structural simplicity and easy installation benefits. and has good running efficiency under normal designed condition. But under extreme climate condition (over +30℃, under -10℃), this system exposes abnormal power consumption. It causes high progressive electric power rates and resultant peak power capacity of power plant. In this paper, a novel system concept of buffering refrigerant accumulator and constant pressure control system to relieve peak power load is proposed and this system’s utility is verified with an prototype experimental system

Accumulator (cryptography)

Cooling capacity

Constant (computer programming)

Condenser (optics)

10.5207/jieie.2015.29.11.053

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Risk of Stroke after Vaccination against COVID19 in Patients with Moyamoya Disease: Nationwide Cohort Observational Study

Research Square (Research Square) (2024)

Hyoung Soo Byoun Si Un Lee Yu Deok Won Taewon Choi Sang Hyo Lee

Abstract The safety and efficacy of coronavirus disease 2019 (COVID-19) vaccination in patients diagnosed with Moyamoya disease (MMD) have not been established. Using National Health Insurance Service data, this study analyzed the occurrence of stroke-related events and mortality following COVID-19 vaccination among patients diagnosed with MMD from 2008 to 2020. Among 10,297 MMD patients, 296 (2.9%) experienced stroke-related events and 175 (1.7%) died in 2021. Significant risk factors for events included ages 50–59 (Odds Ratio [OR] 3.29; P = 0.022) and 60 or above (OR 5.20; P = 0.001), low BMI (OR 2.00; P = 0.011), previous stroke (OR 1.96; P < 0.001), and COVID-19 infection (OR 2.28; P = 0.034). Female (OR 0.64; P = 0.011), revascularization surgery (RS) (OR 0.38; P < 0.001), and vaccination (OR 0.17; P < 0.001) were protective. For mortality, significant risks were age over 60 (OR 7.09; P = 0.008), low BMI (OR 3.87; P = 0.001), and prior stroke (OR 1.74; p = 0.004), while being female, RS (OR 0.41; P = 0.022), and vaccination (OR 0.12; P < 0.001) were preventive. mRNA vaccines were more effective than vector vaccines in preventing events, mortality, and COVID19 infections. COVID-19 vaccination significantly reduces stroke-related events and mortality in MMD patients, with mRNA vaccines being more effective. COVID-19 infection raises the risk of events, underscoring the benefit of vaccination.

Stroke

Moyamoya Disease

Stroke risk

10.21203/rs.3.rs-4639766/v1

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Reversible cerebral vasoconstriction syndrome presenting with intracranial hemorrhage: a case report and literature review

Journal of Korean Society of Geriatric Neurosurgery (2021)

Taewon Choi Hee Sup Shin Seung Hwan Lee Jun Seok Koh Hak Cheol Ko

Reversible cerebral vasoconstriction syndrome (RCVS) is characterized by a severe thunderclap headache associated with segmental vasoconstriction of the cerebral arteries. RCVS may result in intracranial hemorrhage (ICH), but the pathophysiology and data of RCVS-related ICH are not well known. The authors report a case of RCVS that presented with intraparenchymal hemorrhage (IPH) and subarachnoid hemorrhage (SAH). A 66-year-old female presented with recurrent thunderclap headache, and her initial consciousness and neurologic status were normal. Brain computed tomography (CT) revealed IPH in the left frontal cortex and SAH in the left Sylvian fissure. CT angiography and digital subtraction angiography showed multiple segmental vasoconstrictions in the M3 segments of the left middle cerebral artery, but intracranial aneurysm or vascular malformation was not observed. After nimodipine infusion and pain control, the headache subsided, and she was discharged without neurologic deficits. Three months after symptom onset, the segmental vasoconstrictions disappeared on cerebral magnetic resonance angiography. Clinicians should be aware of RCVS as a possible cause of non-aneurysmal SAH and IPH in an unusual location. Keywords: Vasoconstriction; Subarachnoid hemorrhage; Intracranial hemorrhages; Headache

Nimodipine

Intraparenchymal hemorrhage

Digital subtraction angiography

Magnetic resonance angiography

10.51638/jksgn.2021.00087

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Comparison of Current and Novel ECG-Independent Algorithms for Resting Pressure Derived Physiologic Indices

IEEE Access (2019)

Ki Hong Choi Jinhyoung Park Joo Myung Lee Taewon Choi Young Bin Song

Recently, instantaneous wave-free ratio (iFR) or diastolic pressure-ratio (dPR) have been used in practice. For these indices, the reliability of electrocardiography (ECG)-independent algorithm for pressure-only data is essential. The current study sought to compare the current to a new ECG-independent algorithm for calculating resting physiologic indices. The main purpose of developing a new ECG-independent algorithm was to raise the detection rates over the entire heart cycle despite irregular heartbeats. Both iFR and dPR were calculated from resting pressure tracings using current and new algorithms by a core laboratory in 975 vessels (393 patients). The diagnostic performance of resting physiologic indices with a new algorithm to predict fractional flow reserve (FFR) was compared with the current algorithm. Both algorithms provided nearly identical values of iFR or dPR without systemic bias. iFR and dPR, which were calculated using current and new ECG-independent algorithms, provided comparable discrimination ability and diagnostic performance to predict functionally significant stenosis defined by FFR≤0.80. However, detection rates of the new algorithm were significantly higher than current algorithm in the patients with irregular heartbeats (for per patient [59.5% vs. 83.8%] and per unit-heartbeats analysis [84.3% vs. 90.3%]), such as arterial fibrillation or multiple premature ventricular contractions.

Fractional Flow Reserve

10.1109/access.2019.2940085

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Citations (2)

Total pelvic exenteration and reconstruction for locally invasive recurrent sarcoma of the perineum.

PubMed (2000)

Weiss Re Brogle Bn Ravikumar Ts Taewon Choi Cummings Kb

Extensive primary tumors and locally recurrent tumors of the pelvis or perineum are difficult to manage. We describe the techniques necessary to perform total pelvic exenteration with en bloc resection of the perineum and genitalia for treatment of recurrent sarcoma of the perineum. Wide excision of the sarcoma with negative margins can be achieved by resecting the inferior portion of the pubic symphysis. An absorbable mesh sling may be used to suspend the small bowel above the pelvis, facilitating postoperative radiation. A catheterizable continent urinary reservoir avoids the necessity of two stomas and improves quality of life. Adequate tissue coverage can be attained by myocutaneous gracilis flaps that promote wound healing.

Pelvic exenteration

Hemipelvectomy

Sling (weapon)

Source

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Citations (1)

Strong Coupling Induced Bound States in the Continuum in a Hybrid Metal–Dielectric Bilayer Nanograting Resonator

ACS Photonics (2024)

Hyunwoo Son Taewon Choi Kyuho Kim Youngjin Kim Junseo Bang

In the field of modern optics, the capability of localizing light at the nanoscale is crucial. Recently, the concept of the bound state in the continuum (BIC) has emerged, demonstrating highly resonant photonic modes within lossless dielectric nanostructures. On the contrary, implementing BICs with plasmonic resonators, despite its distinct advantages of near-field concentration, has been less preferred due to inherent material losses. This study proposes a novel BIC nanoresonator utilizing a hybrid metal–dielectric bilayer nanograting. In this structure, the metallic upper nanograting functions as a concentrator of the incident wave, whereas the dielectric lower nanograting serves as the main resonator for the concentrated field, exhibiting negligible material loss. This design facilitates strong near-field coupling between the three modes induced within the hybrid nanograting, leading to the emergence of BIC with exceptional quality factors. Our comprehensive analysis, including theoretical, numerical, and experimental investigations, reveals that the attainment of strong coupling is followed by the formation of BIC, while distinct mode hybridization and large Rabi splitting energy of about 436 meV are observed. As a result, an enhancement of more than 8-fold in electromagnetic energy is achieved within a silicon nanograting compared with the conventional single-layer resonator. It is worth noting that the trade-off between the intensity and storage lifetime of confined energies is addressed and the novel formation principle of the strong coupling induced BIC at the Γ-point is unveiled via temporal and spatial coupled mode theories for the first time, to the best of our knowledge. Our findings are expected to enhance the functionalities of resonant nanophotonic applications.

Coupled mode theory

10.1021/acsphotonics.4c00602

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Citations (3)

Golay-Coded Excitations for Rotational Intravascular Ultrasound Imaging

IEEE Access (2019)

Taewon Choi Seoyun Chang Tae‐Hyung Kim Jinhyoung Park

Intravascular ultrasound (IVUS) imaging employs high imaging frequencies (from 20 to 60 MHz) to visualize microvascular structures by sacrificing the depth of penetration with an increased signal attenuation.To compensate for the reduced echo signal-to-noise ratio, chirp-coded excitations, which require complex system configurations in high-frequency ultrasound imaging, are considered as suitable methods for rotational IVUS.Golay-coded excitations, which only need simple electronics and have no range sidelobe artifacts if the incident locations of the Golay pair are the same, have not been considered for rotational IVUS.In this study, computer simulations and experiments with a custom-made IVUS imaging system running at 30 fps are performed to investigate on the optimal operational conditions of Golay-coded excitations in rotational IVUS imaging.While the code length was not a significant factor affecting the range sidelobe level (RSLL), a change in the imaging frequency from 25 MHz to 66 MHz increased the RSLL from -65 dB to -45 dB with 2048 beamlines.In addition, an increase in the number of beamlines from 64 to 2048 reduced the RSLL from -17 dB to -50 dB in the simulation and from -14 dB dB to -38 dB in the experiment.To further decrease the RSLL, a weighted averaging method that compressed the coded pulse was proposed.The RSLL could be suppressed from -50 dB to -80 dB and from -38 dB to -53 dB in the simulation and experiment, respectively.Golay-coded excitation imaging was also successfully demonstrated on freshly harvested pig coronary arteries. INDEX TERMS Intravascular ultrasound, Golay-coded

Binary Golay code

Intravascular Ultrasound

Chirp

10.1109/access.2019.2936462

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Citations (5)