Hyungil Seo

Comparative analysis of radiofrequency ablation and resection for resectable colorectal liver metastases

AIM To evaluate the therapeutic efficacy of radiofrequency ablation (RFA) for resectable colorectal liver metastases (CRLM) compared with that of resection. METHODS Between June 2004 and June 2009, we retrospectively analyzed 29 patients with resectable CRLMs; 17 patients underwent RFA, and 12 underwent hepatic resection. All of the patients were informed about the treatment modalities and were allowed to choose either of them. RFA including an intraoperative approach was performed by a radiologist; otherwise, hepatic resection was performed by a surgeon. Comparative analysis of the two groups was performed, including comparisons of gender, age, and clinical outcomes, such as primary tumor stage and survival rates. RESULTS The mean tumor size was significantly larger in the resection group (3.59 cm vs 2.02 cm, P < 0.01), and the 5-year overall survival (OS) rate for all patients was 44.7%. There was no difference in the 5-year OS rates between the RFA and resection groups (37.8% vs 66.7%). Univariate analysis indicated significantly lower 5-year OS rates for patients with a tumor size > 3 cm. The 5-year disease-free survival (DFS) rates were 17.6% and 22.2% in the RFA and resection groups, respectively (P = 0.119). Univariate analysis revealed that in cases of male gender, age > 65 years, T stage < IV, absence of lymphatic metastasis, and tumor size > 3 cm, RFA resulted in significantly inferior 5-year DFS rates compared with surgical resection. CONCLUSION Surgical resection revealed superior outcomes in the treatment of resectable CRLMs, particularly in cases with a hepatic tumor size > 3 cm.

Compensation of Raman-induced crosstalk using a lumped germanosilicate fiber Raman amplifier in the 1.571-1.591-μm region

A new method to equalize power imbalance caused by Raman-induced crosstalk among optical channels is proposed using a lumped germanosilicate fiber Raman amplifier. Evolution of optical channels through the Raman amplifier was simulated using Raman frequency modeling, which theoretically predicted simultaneous amplification and power equalization. Experimentally, a gain band with negative slope in the range of 1.571-1.591 /spl mu/m was achieved in a lumped Raman amplifier pumped by a broad-band laser diode centered at 1.467 /spl mu/m. We demonstrated compensation of the Raman-induced crosstalk of 5 dB accumulated along 330 km of conventional single-mode fiber.

Gain optimization of germanosilicate fiber Raman amplifier and its applications in the compensation of Raman-induced crosstalk among wavelength division multiplexing channels

Spectral characteristics of the stimulated Raman scattering (SRS) process were theoretically investigated for step-index silica optical fibers with various GeO/sub 2/ concentrations. Optimal-fiber lengths and germanium concentration, where the first Stokes power reaches maximum, were calculated at various pump power levels for application in Raman amplifiers. Based on this analysis, we proposed and experimentally demonstrated a new channel-equalizing technique to simultaneously compensate Raman-induced crosstalk and amplify wavelength-division-multiplexing (WDM) signals using a discrete Raman amplifier in the 1.5-/spl mu/m range. As a further application of SRS in germanosilicate glass fibers, we introduce an all-optical variable attenuator for channel equalization that could be used in dynamic optical power tilt control in WDM systems.

Polarization dependent dispersion characteristics of high order modes in a cylindrical dual mode fiber with an arbitrary index profile

Abstract For a cylindrical dual mode optical fiber, dispersion characteristics of the high order polarization modes, TE 01 , TM 01 , and HE 21 , have been rigorously analyzed by solving the vectorial Maxwell equations numerically. The effects of the inner cladding index structure on the dispersion characteristics of the polarization modes are reported for the first time. In the matched cladding, the difference in chromatic dispersion, dispersion slope and modal delay among the polarization modes are found to increase for waveguide conditions optimized for a large negative dispersion. A new design of a cylindrical dual mode fiber with a depressed inner cladding that can intrinsically reduce the polarization dependence in the dispersion characteristics to improve the performance in dispersion compensation is proposed.

Broadband polarization-insensitive all-fiber acousto-optical modulator

Summary form only given. We have demonstrated a broadband, polarization insensitive, low-loss acousto optical (AO) modulator by using a two-mode fiber designed to provide a flat-top broadband spectral response. The device has a simple all-fiber construction, and can be a potentially low-cost AO modulator for compensating add/drop power transients of EDFAs over the whole gain band in WDM communication systems.

Underestimation of Smoking Rates in an East Asian Population with Crohn’s Disease

Background/Aims The reported rates of current smoking at the time of Crohn’s disease (CD) diagnosis tend to be low in East Asian studies. However, we hypothesized that East Asian patients may be reluctant to disclose their smoking history, likely because of the influence of the Confucian culture. Methods We prospectively re-evaluated the smoking status at diagnosis in 1,437 Korean CD patients whose smoking status had been reported in our previous study. Results After re-evaluation, the current smokers at diagnosis increased from 388 patients (27.0%) to 445 patients (31.0%), indicating that 12.8% (57 of 445 patients) of the current smokers at diagnosis did not disclose their smoking status at their initial evaluation. The proportion of current smokers at diagnosis who had initially concealed their smoking status was significantly higher among the female patients (29.7%, 11/37) compared with the male patients (11.3%, 46/408) (p<0.005) and among the patients who were ≤18 years old at diagnosis (56.4%, 22/39) compared with the patients >18 years old at diagnosis (8.6%, 35/406) (p<0.001). Conclusions Subgroups of Korean CD patients, particularly young patients and female patients, are reluctant to disclose their smoking history. Therefore, the suggestion that smoking is not a risk factor for the development of CD in East Asians should be made with caution.

Enhancement of butt-coupling pump efficiency in a new Nd-doped large core double clad fiber laser cavity adiabatically tapered at both ends

Summary form only given. A new clad pumped fiber laser cavity structure has been proposed and experimentally demonstrated. Double adiabatic tapers included in the cavity provided inherent highly mode-selective attenuation to the lasing photons guided through the core with an improved butt-coupling efficiency for the pump light. Filtering of high order modes at the lasing wavelength was confirmed by measurement of the far-field pattern of the laser output. Output power 820 mW was achieved for the coupled pump power of 5.8 W which could be further improved by reduction of helical waves in pump light.

Design of transmission optical fiber with a high Raman gain, large effective area, low nonlinearity, and low double Rayleigh backscattering

Designed was the transmission fiber with a high Raman gain, large effective area, low nonlinearity, and low double Rayleigh backscattering (DRBS). Basically the optical signal-to-noise ratio (OSNR) of distributed type Raman amplifier is superior to that of the lumped type Raman amplifier using a high Raman gain fiber such as dispersion compensation fiber. However, much pump power and long length of transmission fiber line are required to acquire a proper gain in the distributed type fiber Raman amplifier. Thus, compositional adjustment on the fiber for optical transmission is of benefit to reduce further the required pump power. In this regard, based on this simulation, the fluorine and germanium co-doped fiber showed a high Raman gain, high OSNR, and low DRBS.

Study on the design of non-zero dispersion shifted fiber for ultra-wide band WDM transmission

We describe the modified structure of non-zero dispersion shifted fiber for ultra-wide band (from 1450 nm to 1650 nm) WDM transmission. We demonstrate the improvement in the dispersion over a wavelength range of 1450 nm to 1650 nm due to modified fiber design in simulation. The tolerances of core radius and clad radius are also discussed.

Does the pancreatic volume reduction rate using serial computed tomographic volumetry predict new onset diabetes after pancreaticoduodenectomy

Abstract Volume reduction of the pancreatic tissues following a pancreatectomy can lead to the deterioration of glucose homeostasis. This is defined as pancreatogenic diabetes mellitus (DM). The objective of this study was to investigate the occurrence of new-onset DM (NODM) and evaluate the risk factors, including the pancreas volume reduction rate in patients undergoing pancreaticoduodenectomy (PD). Sixty-six patients without preoperative DM underwent PD for periampullary tumors between August 2007 and December 2012 and were included in this analysis. These patients underwent follow-up tests and abdominal computed tomography (CT) scan 7 days, 6 months, 12 months, 24 months, and 36 months after the operation. The pancreas volume reduction rate was calculated by CT volumetry. The patients were divided into 2 groups according to the postoperative development of DM. After PD, newly diagnosed DM occurred in 16 patients (24.2%). The incidence of DM was highest among patients with carcinomas with an advanced T stage. The pancreatic volume reduction rate after 6 and 12 months in the NODM group was significantly higher than the normal glucose group in the univariate analysis. In the multivariate analysis, the pancreatic volume reduction rate 6 months after PD was the only significant predictive factor for the development of NODM (P = 0.002). This study suggests that the pancreatic volume reduction rate 6 months after PD was the only significant predictive factor for the development of NODM. CT volumetry of the pancreas may be useful as a predictor of NODM after PD.