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Choi, Kihwan,Wang, Jing,Zhu, Lei,Suh, Tae-Suk,Boyd, Stephen,Xing, Lei Wiley (John WileySons) 2010 Medical physics Vol.37 No.9
<P>PURPOSE: This article considers the problem of reconstructing cone-beam computed tomography (CBCT) images from a set of undersampled and potentially noisy projection measurements. METHODS: The authors cast the reconstruction as a compressed sensing problem based on l1 norm minimization constrained by statistically weighted least-squares of CBCT projection data. For accurate modeling, the noise characteristics of the CBCT projection data are used to determine the relative importance of each projection measurement. To solve the compressed sensing problem, the authors employ a method minimizing total-variation norm, satisfying a prespecified level of measurement consistency using a first-order method developed by Nesterov. RESULTS: The method converges fast to the optimal solution without excessive memory requirement, thanks to the method of iterative forward and back-projections. The performance of the proposed algorithm is demonstrated through a series of digital and experimental phantom studies. It is found a that high quality CBCT image can be reconstructed from undersampled and potentially noisy projection data by using the proposed method. Both sparse sampling and decreasing x-ray tube current (i.e., noisy projection data) lead to the reduction of radiation dose in CBCT imaging. CONCLUSIONS: It is demonstrated that compressed sensing outperforms the traditional algorithm when dealing with sparse, and potentially noisy, CBCT projection views.</P>
Purity assessment using quantitative NMR: establishment of SI traceability in organic analysis
Choi, Kihwan Korean Magnetic Resonance Society 2020 Journal of the Korean Magnetic Resonance Society Vol.24 No.1
Quantitative nuclear magnetic resonance (qNMR) has been gaining attention as a purity assessment method. In particular, qNMR is recognized as the primary method to realize the Internal System of Units (SI) in organic analysis. The capability of quantitative analysis is recognized as the beginning of NMR development. NMR signals are proportional to the number of nuclei and qNMR has been used in various fields, such as metabolomics and food and pharmaceutical analysis. However, careful sample preparation and thorough optimization of measurement parameters are required to obtain accurate and reliable results. In this review, quantitative methods used in qNMR are discussed, and the important factors to be considered also introduced. The recent development of qNMR techniques including combination with chromatography and, multidimensional NMR are also presented.
Choi Kihwan,Park Jong Eun,Kim Anhye,Hwang Sojung,Bae Jinkun,Shin Tae Gun,Kim Kyuseok 대한응급의학회 2022 Clinical and Experimental Emergency Medicine Vol.9 No.3
Objective Steroids are used in cases of sepsis, especially in patients experiencing septic shock. However, clinical trials to date have reported contradictory results. Different patient endotypes and variations in the type and dose of steroid may be at fault for this discrepancy, and further investigation is warranted. In this paper, we propose a new DEXA-SEPSIS study design. Methods We plan to conduct a multicenter, double-blinded randomized pilot study (DEXA-SEPSIS) investigating the feasibility and safety of early use of dexamethasone in sepsis. Participants will be high-risk septic patients presenting to the emergency department with a systolic blood pressure of <90 mmHg or serum lactate level of >2 mmol/L. Participants will be randomized to the following three groups: control, 0.1 mg/kg of dexamethasone, or 0.2 mg/kg of dexamethasone per day for 1 to 2 days. The primary outcome will be 28-day mortality. Secondary outcomes will include time to septic shock, shock reversal, additional steroid administration, number of ventilator-free days, use of continuous renal-replacement therapy, length of stay in the intensive care unit and/or hospital, delta Sequential Organ Failure Assessment score on days 3 and 7, superinfection, gastrointestinal bleeding, hypernatremia, and hyperglycemia. Discussion The DEXA-SEPSIS study will provide insight regarding the feasibility and safety of early use of dexamethasone in high-risk sepsis. The results could provide data to design a future phase III study.
Single-drop microextraction in bioanalysis.
Choi, Kihwan,Kim, Jihye,Chung, Doo Soo Future Science 2011 Bioanalysis Vol.3 No.7
<P>Bioanalysis usually requires a preparation procedure for sample cleanup or preconcentration. Conventional sample preparation techniques are often time consuming and labor intensive. Among recent progress in sample preparation, single drop microextraction (SDME) is one of the most efficient techniques providing both sample cleanup and preconcentration capabilities. In SDME, analytes are extracted from a sample solution into an acceptor drop and the drop is introduced to subsequent analysis. Since the volume of the acceptor drop is 1-10 µl or less, the consumption of solvents can be minimized and the preconcentration effect is enhanced. In this review, the basic principles of two-phase and three-phase SDME are described briefly and then recently developed modes of SDME, coupling with analytical instruments, and methods to enhance the drop stability are discussed. Recent applications of SDME to biological samples, including urine, blood and saliva, for the analysis of drugs, metal ions and biomarkers are reviewed.</P>
Choi, Kihwan,Jin, Yoo Gon,Chung, Doo Soo Elsevier 2009 Journal of chromatography A Vol.1216 No.37
<P><B>Abstract</B></P><P>In order to improve the concentration sensitivity of capillary electrophoresis (CE), two sample preconcentration techniques, single drop microextraction (SDME) and large volume stacking using an electroosmotic flow pump (LVSEP), were coupled in-line in a commercial CE instrument. By simple programming of liquid handling sequences, a pentanol drop was prepared at the tip of a fused silica capillary over which a Teflon tube had been sleeved to serve as a hydrophobic support. After extraction of the analytes from an aqueous donor solution into the drop, the entire capillary column was filled with enriched pentanol extract. LVSEP, in which the sample matrix is automatically removed by the EOF, was then carried out using a methanolic run buffer. The overall enrichment factors for the analytes pentachlorophenol (PCP), 3-bromobenzoic acid (3-BBA), and 4-iodobenzoic acid (4-IBA), from a combination of 30min SDME and LVSEP on a 27cm capillary, were about 7000, even without agitation of the donor solution. The resulting limits of detection for PCP, 3-BBA, and 4-IBA were 0.7, 0.3 and 0.7nM, respectively. Since no modification of the existing CE instrument is necessary and a bare capillary is used for LVSEP, this scheme can be adapted quite easily for many CE applications that require high concentration sensitivity.</P>
Han, Kihwan,Choi, Jae Hoon,Choi, Tae Hyun,Jeon, Sea Yuong,Kim, Jun Sik,Kim, Nam Gyun,Lee, Kyung Suk,Son, Daegu,Kim, Jun Hyung,Kim, Sang-Hyon,Kang, Dawon,Park, Jungbin Lippincott Williams Wilkins, Inc. 2009 Annals of plastic surgery Vol.62 No.3
Currently, endoscopic endonasal reduction and transcaruncular reduction are frequently used as surgical treatments for medial orbital wall fractures. However, these 2 surgical techniques have not been comprehensively compared using objective criteria. Therefore, the results of these 2 techniques were compared retrospectively using 8 objective criteria in patients with medial orbital wall fracture.This study included 48 medial orbital wall fracture patients treated from June 1993 to July 2006: 29 had endoscopic endonasal reduction and 19 had transcaruncular reduction. Computed tomographic scans, double vision field testing for diplopia using Goldmann perimetry, and Hertel exophthalmometer (Richmond Products, Albuquerque, NM) were done pre- and postsurgery.The average follow-up period was 70.8 months. Among patients with pure medial orbital wall fractures, the average reduction rate was 89.2% for the endoscopic endonasal reduction group and 90.7% for the transcaruncular reduction group. One case in the endoscopic endonasal reduction group had a more than 2-mm enophthalmos after surgery. The diplopia correction rate was 1.8% in the endoscopic endonasal reduction group and 2.7% in the transcaruncular reduction group. None of the above differences was statistically significant. However, among patients with pure medial orbital wall fractures compared with the transcaruncular reduction group, the average operation time, the average hospital stay, and the average cost were significantly greater in the endoscopic endonasal reduction group.The 2 surgical methods had a similar effectiveness; however, transcaruncular reduction seemed to be more advantageous with respect to the operation time, the length of hospital stay, and cost.