Biomedical subjects

Y C Chung

Publications and source records attributed to Y C Chung.

At least 37 records · Page 2Linked to original sources

PubMed2001

Purification and characterization of a dimethoate-degrading enzyme of Aspergillus niger ZHY256, isolated from sewage.

A dimethoate-degrading enzyme from Aspergillus niger ZHY256 was purified to homogeneity with a specific activity of 227.6 U/mg of protein. The molecular mass of the purified enzyme was estimated to be 66 kDa by gel filtration and 67 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The isoelectric point was found to be 5.4, and the enzyme activity was optimal at 50 degrees C and pH 7.0. The activity was inhibited by most of the metal ions and reagents, while it was induced by Cu(2+). The Michaelis constant (K(m)) and V(max) for dimethoate were 1.25 mM and 292 micromol min(-1) mg of protein(-1), respectively.

Aspergillus niger↗

PubMed2000

Biotreatment of H2S- and NH3-containing waste gases by co-immobilized cells biofilter.

Gas mixture of H2S and NH3 in this study has been the focus in the research area concerning gases generated from the animal husbandry and the anaerobic wastewater lagoons used for their treatment. A specific microflora (mixture of Thiobacillus thioparus CH11 for H2S and Nitrosomonas europaea for NH3) was immobilized with Ca-alginate and packed inside a glass column to decompose H2S and NH3. The biofilter packed with co-immobilized cells was continuously supplied with H2S and NH3 gas mixtures of various ratios, and the removal efficiency, removal kinetics, and pressure drop in the biofilter was monitored. The results showed that the efficiency remained above 95% regardless of the ratios of H2S and NH3 used. The NH3 concentration has little effect on H2S removal efficiency, however, both high NH3 and H2S concentrations significantly suppress the NH3 removal. Through product analysis, we found that controlling the inlet ratio of the H2S/NH3 could prevent the biofilter from acidification, and, therefore, enhance the operational stability. Conclusions from bioaerosol analysis and pressure drop in the biofilter suggest that the immobilized cell technique creates less environmental impact and improves pure culture operational stability. The criteria for the biofilter operation to meet the current H2S and NH3 emission standards were also established. To reach Taiwan's current ambient air standards of H2S and NH3 (0.1 and 1 ppm, respectively), the maximum inlet concentrations should not exceed 58 ppm for H2S and 164 ppm for NH3, and the residence time be kept at 72 s.

Air Pollutants↗

PubMed1999

Temperature measurement using echo-shifted FLASH at low field for interventional MRI.

We investigated the feasibility of using echo-shifted fast low-angle shot (FLASH) for temperature-monitored thermo-therapeutic procedures in a 0.2 T interventional magnetic resonance (MR) scanner. Based on the proton resonance frequency shift technique, modified echo-shifted FLASH has sufficiently high signal-to-noise ratio to provide accurate temperature maps with short scan times, i.e., 5 seconds in phantoms (TR = 20.5 msec; effective TE = 30 msec; one echo shift; NSA = 2) and ex vivo experiments (TR = 19.4 msec; effective TE = 28.9 msec; one echo shift; NSA = 2) and 3 seconds (TR = 19.4 msec; effective TE = 28.9 msec, one echo shift; NSA 1) for an in vivo case. The proton resonance frequency shifts with temperature observed in a 0.2 T MR scanner using this sequence were -0.0072 ppm/degrees C (temperature uncertainty = +/-2.5 degrees C) for polyacrylamide phantoins and -0.0086 ppm/degrees C (temperature uncertainty = +/- 1 degrees C) for ex vivo bovine liver. These experiments demonstrated that echo-shifted FLASH is a viable method for low-field temperature monitoring despite the decreased signal and decreased phase sensitivity compared with its counterpart in a 1.5 T MR imaging system. The improved temporal resolution of temperature images, now possible in low-field interventional MR systems using echo-shifted FLASH, will allow clinicians more accurate monitoring of interstitial ablation in MR-guided interventional procedures.

Animals↗

PubMed1999

MRI-guided radiofrequency thermal ablation of implanted VX2 liver tumors in a rabbit model: demonstration of feasibility at 0.2 T.

Successful radiofrequency (RF) thermal ablation was performed on VX2 tumors implanted in 23 rabbit livers under magnetic resonance (MR) guidance using a C-arm-shaped low-field 0.2 T system. RF application and immediate postprocedure MRI of all animals was performed [T2-weighted, turbo short tau inversion recovery (STIR), T1-weighted before and after gadopentetate dimeglumine administration). Follow-up MRI with a superparamagnetic iron oxide (SPIO) contrast medium was performed in nine rabbits at 2 weeks and in four rabbits at 1 month post RF ablation. All livers were harvested for pathologic examination. T2-weighted and turbo-STIR images demonstrated the highest tumor-to-RF-thermal lesion contrast-to-noise ratios (CNRs; means 4.5 and 3.8, respectively) on postprocedure images; this was redemonstrated at 2- and 4-week follow-up imaging. T2-weighted imaging never overestimated pathologic lesion size by more than 2 mm, and the radiologic-pathologic correlation coefficient was not less than 0.90. In conclusion, MRI-guided RF thermal ablation in implanted liver tumor is feasible using a C-arm-shaped low-field 0.2 T system. The thermal lesion size can be most accurately monitored with T2-weighted and turbo-STIR images.

Animals↗

PubMed1999

Fast T(2)-weighted imaging by PSIF at 0.2 T for interventional MRI.

Rapid T(2) weighted (T(2)W) images would facilitate physicians being able to distinguish normal tissues, vessels, tumors, and thermal lesions from therapeutic devices throughout interventional MRI procedures commonly performed in open low-field scanners (e.g., 0.2 T). Conventional diagnostic MRI techniques have not been successful at low-field strength for fast T(2)W imaging during the guidance phase of interventional MRI (I-MRI) procedures. FISP and true-FISP methods yield T(1)/T(2)-weighted images and do not always provide sufficient contrast for device guidance or lesion assessment. As such, a variant of PSIF (a gradient reversed form of FISP) which collects the T(2)-weighted spin echo of the SSFP signal was developed and implemented at 0.2 T for use in I-MRI procedures. The sequence has a balanced readout gradient to reduce motion sensitivity. Asymmetric sampling toward the end of the TR cycle reduces T(2)* decay of the spin echo component in the SSFP signal. The sequence gives one image in 5-7 s in vivo with adequate SNR and T(2) contrast for interventional applications. Patient studies showed that the PSIF sequence variant demarcates many tumors not detectable by either FISP or true-FISP. Results from animal experiments suggested that it has potential to monitor thermal lesions during interstitial thermal ablation procedures. Magn Reson Med 42:335-344, 1999.

Animals↗

PubMed1999

Signal formation in echo-shifted sequences.

Echo shifted (ES) gradient-recalled echo sequences (whose TE > TR) have found important applications in fMRI and MR thermometry since their introduction. The technique increases T *(2) weighting in BOLD imaging and temperature change sensitivity in phase-based temperature imaging compared to FLASH sequences. Yet, inconsistent observations have previously been reported when variants of this technique were used in various MRI experiments. Previous understanding of the ES sequences (the "FLASH-like" postulation) was not sufficient to explain these observations. This work provides an in-depth study on the various ES sequences. It was found that there are two types of ES sequences: ES-FLASH that spoils coherent transverse magnetization and ES-GRE, which is based on SSFP signals. A signal expression was derived for the clinically popular TR-periodic ES-GRE sequence with one echo shift. This signal expression reduced to the "FLASH-like" postulation under certain conditions. The new knowledge about the echo formation mechanism in ES sequences helps explain the experimental observations previously reported. Moreover, the resonance offset angle based analysis demonstrates an elegant methodology to analyze short TR imaging sequences. Magn Reson Med 42:864-875, 1999.

Brain↗

PubMed1998

Epidemiology of eating disordered symptoms in the Korean general population using a Korean version of the Eating Attitudes Test.

OBJECTIVE: The purposes of the present study were to estimate the proportion of subjects with a high score on the Korean version of Eating Attitudes Test--26 (KEAT-26), which may provide preliminary data regarding the prevalence rate of eating disorders in the Korean general population, and to further examine the sociocultural hypothesis of eating disorders. METHOD: Using a multi-stage questionnaire sampling method, we surveyed 3062 subjects (1249 males, 1813 females) from 3896 Korean adults in a nationwide area. RESULTS: 8.5% (260/3062) of subjects scored above the cut-off on the KEAT-26. Their demographic correlates, eating traits, and other characteristics relating to general psychopathology were similar to those of patients with eating disorders and female Caucasian controls in Western countries. DISCUSSION: These results suggest that changes in various sociocultural aspects have increased the risk of developing eating disorders in Korea, and support the sociocultural hypothesis of eating disorders.

Adult↗

PubMed1998

[Pulse sequences and visualization of instruments].

While initially advocated primarily for intrasurgical visualization (e.g., craniotomy), interventional MRI rapidly evolved into roles in image-guided localization for needle-based procedures, and thermal ablation of cancer. In this contest, MRI pulse sequences and scanning methods serve one of four primary roles: (1) speed improvement, (2) device localization, (3) anatomy/lesion differentiation and (4) temperature sensitivity. The first part of this manuscript deals with passive visualization of MR-compatible needles and the effects of field strength, sequence design, and orientation of the needle relative to the static magnetic field of the scanner. Issues and recommendations are given for low-field as well as high-field scanners. The second part contains methods reported to achieve improved acquisition efficiency over conventional phase encoding (wavelets, locally focused imaging, singular value decomposition and keyhole imaging). Finally, the last part of the manuscript reports the current status of thermosensitive sequences and their dependence on spinlattice relaxation time (T1), were diffusion coefficient (D) and proton chemical shift (delta).

Animals↗

PubMed1998

Methods for providing probe position and temperature information on MR images during interventional procedures.

Interventional magnetic resonance imaging (MRI) can be defined as the use of MR images for guiding and monitoring interventional procedures (e.g., biopsy, drainage) or minimally invasive therapy (e.g., thermal ablation). This work describes the development of a prototype graphical user interface and the appropriate software methods to accurately overlay a representation of a rigid interventional device [e.g., biopsy needle, radio-frequency (RF) probe] onto an MR image given only the probe's spatial position and orientation as determined from a three-dimensional (3-D) localizer used for interactive scan plane definition. This permits 1) "virtual tip tracking," where the probe tip location is displayed on the image without the use of separate receiver coils or a "road map" image data set, and, 2) "extending" the probe to predict its path if it were directly moved forward toward the target tissue. Further, this paper describes the design and implementation of a method to facilitate the monitoring of thermal ablation procedures by displaying and overlaying temperature maps from temperature sensitive MR acquisitions. These methods provide rapid graphical updates of probe position and temperature changes to aid the physician during the actual interventional MRI procedures without altering the usual operation of the MR imager.

Animals↗

PubMed1997

Analysis of biomass cellulose in simultaneous saccharification and fermentation processes.

A direct method for determining the cellulose content of biomass residues resulting from simultaneous saccharifiaction and fermentation (SSF) experiment has been developed and evaluated. The method improves on classical cellulose assays by incorporating the enzymatic removal of yeast glucans from the biomass residue prior to acid hydrolysis and subsequent quantification of cellulose-derived glucose. An appropriate cellulase-free, commercially available, yeast-lysing enzyme preparation from Cytophaga was identified. A freeze-drying step was identified as necessary to render the SSF yeast cells susceptible to enzymatic lysis. The method was applied to the analysis of cellulose and yeast-associated glucans in SSF residues from three pretreated feedstocks; hybrid poplar, switchgrass, and cornstover. Cellulose assays employing the lysing-enzyme preparation demonstrated relative errors up to 7.2% when yeast-associated glucans were not removed prior to analysis of SSF residues. Enzymatic lysis of SSF yeast cells may be viewed as a general preparatory procedure to be used prior to subsequent chemical and physical analysis of SSF residues.

Biomass↗

PubMed1997

Generation and observation of radio frequency thermal lesion ablation for interventional magnetic resonance imaging.

RATIONALE AND OBJECTIVES: Recently, there has been increased interest in interventional magnetic resonance (MR) imaging and minimally invasive cancer therapy via radio frequency (RF) thermal ablation. In this work, we examined RF thermal lesion generation in phantoms and ex vivo bovine liver and correlated them with MR images under a variety of conditions, which begins our assessment of the role of MR imaging in this new method for cancer treatment. METHODS: Radio frequency lesions were created in gel phantoms and ex vivo bovine liver, using stationary (bovine liver) and variable speed (gel) moving electrodes to create lesions with shapes mimicking tumors. Ex vivo bovine liver lesions were made with the tissue held at room temperature (n = 4) and in a 37 degrees C saline bath (n = 3) using a 16-gauge electrode (tip temperature: 70 degrees C, 80 degrees C, and 90 degrees C; ablation time: 1-13 minutes). Electrical impedance and RF power were plotted during ablation. After ablation, RF-induced lesions were imaged with a 0.2-tesla (T) MR system using a variety of pulse sequences. RESULTS: Complex shaped lesions were created successfully in phantoms. Averaged maximum ex vivo lesion volume made at 90 degrees C ablation experiments holding the tissue temperature at 37 degrees C and at room temperature were 1.58 +/- 0.35 cm3 and 1.0 +/- 0.26 cm3 respectively (confidence interval: 90%). The aspect ratios and RF power of the lesions decreased as ablations proceeded. Impedance dropped during the first 2 minutes of the ablation. Ex vivo lesions appeared as regions of low-signal amplitude in T2-weighted MR images. CONCLUSIONS: Phantom ablation experience may be useful and applicable in thermotherapy planning. Lesions made in ex vivo bovine liver held at 37 degrees C via a saline bath are larger than those created at room temperature. Lesions shapes are ablation time dependent until thermal equilibrium is reached. Impedance reduction and lesion formation are related; 0.2-T MR systems can image RF energy-induced thermal lesions.

Animals↗

PubMed1996

Continuous hyperthermic peritoneal perfusion for peritoneal carcinomatosis.

Continuous hyperthermic peritoneal perfusion (CHPP) with anticancer agents in warm saline was performed in 10 patients with cancer of the digestive tract and peritoneal carcinomatosis after resection of primary and metastatic lesions or both. Eight patients had colorectal cancer and one patient had recurring gastric cancer. CHPP was performed using saline containing mitomycin-C and 5-flurouracil at 42 degrees C to 43 degrees C for 60 minutes. One patient with pancreatic cancer received CHPP twice. After CHPP, the preoperative ascites of three patients disappeared. Four patients died of malignancy within 1 year of CHPP and one patient died of respiratory failure 5 months post-CHPP. The remaining five patients survived for more than 1 year after CHPP. There were no significant immediate postoperative complications, except for transient changes in liver function, white blood cell count and serum albumin level. While CHPP treatment appears to be a safe method of treatment for peritoneal carcinomatosis, its long term benefits need further investigation.

Adult↗

PubMed1995

Purification and Properties of Extracellular Amylase from the Hyperthermophilic Archaeon Thermococcus profundus DT5432.

A hyperthermophilic archaeon, Thermococcus profundus DT5432, produced extracellular thermostable amylases. One of the amylases (amylase S) was purified to homogeneity by ammonium sulfate precipitation, DEAE-Toyopearl chromatography, and gel filtration on Superdex 200HR. The molecular weight of the enzyme was estimated to be 42,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The amylase exhibited maximal activity at pH 5.5 to 6.0 and was stable in the range of pH 5.9 to 9.8. The optimum temperature for the activity was 80(deg)C. Half-life of the enzyme was 3 h at 80(deg)C and 15 min at 90(deg)C. Thermostability of the enzyme was enhanced in the presence of 5 mM Ca(sup2+) or 0.5% soluble starch at temperatures above 80(deg)C. The enzyme activity was inhibited in the presence of 5 mM iodoacetic acid or 1 mM N-bromosuccinimide, suggesting that cysteine and tryptophan residues play an important role in the catalytic action. The amylase hydrolyzed soluble starch, amylose, amylopectin, and glycogen to produce maltose and maltotriose of (alpha)-configuration as the main products. Smaller amounts of larger maltooligosaccharides were also produced with a trace amount of glucose. Pullulan; (alpha)-, (beta)-, and (gamma)-cyclodextrins; maltose; and maltotriose were not hydrolyzed.

Journal Article↗

PubMed1994

Energy expenditure in patients with hepatocellular carcinoma.

BACKGROUND: An increase in resting energy expenditure (REE) is considered to contribute to the weight loss experienced by patients with cancer. However, alternations in basal metabolism vary among patients with different neoplasms. REE in patients with hepatocellular carcinoma (HCC), a common malignant tumor in Taiwan, was evaluated. METHODS: Fifty-seven male patients with HCC and 60 male control subjects without known cancer were entered in the study. The groups did not differ significantly in age, body weight, and height. Indirect calorimetry was used to measure REE. Oxidative rates of endogenous substrates also were calculated. RESULTS: REE was significantly higher in the HCC group than the control group (22.12 +/- 0.36 kcal/kg/day versus 20.99 +/- 0.27 kcal/kg/day, P < 0.05; and 115.3 +/- 4.3 kcal/100 mg creatinine versus 102.2 +/- 3.8 kcal/100 mg creatinine, P < 0.05). A higher measured-to-predicted-REE ratio also was observed in the HCC group (101.5% +/- 1.4% versus 93.6% +/- 1.0%; P < 0.005). REE in patients with HCC did not differ according to whether patients had liver cirrhosis or ascites. In addition, REE of patients with large and medium tumors were higher than were those of patients with small tumors, but no difference was found between the REE of patients with small tumors and the control subjects. Also observed were an increase in oxidation of fat with a decrease in oxidation of protein in patients with HCC and a relative decrease in the contribution of fat with an increase in the contribution of carbohydrates to REE after the increase of tumor size. CONCLUSIONS: The results suggest that patients with HCC are hypermetabolic and the elevation in REE is related to tumor size, not to the presence of liver cirrhosis or ascites.

Ascites↗

PubMed1994