• Journal of Korea Water Resources Association
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• v.52 no.10
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• pp.657-669
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• 2019

To estimate accurate design quantiles considering statistical characteristics of hydrological data is one of the most important procedures in the design of hydraulic structures. While at-site frequency analysis estimates design quantile using observed data at a site of interest, regional frequency analysis (RFA) utilizes a number of sites included in a hydrologically homogeneous region. Therefore, RFA could provide a more accurate design quantile at ungauged site or sites with short observation period. In this review article, RFA is classified into stationary RFA and nonstationary RFA depending on the characteristic of hydrological data, and the basic concept, procedure, and application of each technique are explained in detail focused on the index flood method. Additionally, a review of the state of the art for RFA procedure is presented. This paper is finalized by describing the stationary regional rainfall frequency analysis over South Korea contained in the amendment of "Standard guidelines for design flood estimation" and various future study topics related to nonstationary RFA.

• Korean Journal of Radiology
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• v.21 no.12
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• pp.1383-1392
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• 2020

Objective: This study aimed to evaluate the efficacy and safety of ultrasound (US)-guided minimally invasive treatment in patients with parathyroid lesions. Materials and Methods: This study included 27 patients who had undergone US-guided radiofrequency ablation (RFA) or ethanol ablation (EA) for parathyroid lesions between January 2010 and 2018. RFA was performed in 19 patients with primary hyperparathyroidism (PHPT, n = 11) or secondary hyperparathyroidism (SHPT, n = 8), and EA was performed in eight patients with symptomatic nonfunctioning parathyroid cysts (SNPCs). Nodule size, volume, serum parathyroid hormone (PTH) and calcium levels were recorded before and after treatment. Complications were evaluated during and after treatment. Results: In patients with PHPT, significant reductions in size and volume were noted after RFA at 6- and 12-month follow-up (all, p < 0.05). Seven nodules nearly completely disappeared (residual volume < 0.1 mL); serum PTH and calcium levels were reduced to normal ranges (7/11, 63.6%). Four patients experienced partial reductions of serum PTH and calcium levels (4/11, 36.4%). In patients with SHPT, three experienced therapeutic response of serum PTH (3/8, 37.5%), while five showed persistent hyperparathyroidism (5/8, 62.5%) within 6 months after RFA. In patients with SNPCs, EA resulted in significant reductions in cyst size and volume (all, p < 0.05) at the last follow-up. A total of four complications (two transient hypocalcemia [RFA], one permanent [RFA], and one transient [EA] hoarseness) were observed. Conclusion: Minimally invasive treatments, such as RFA and EA, may serve as therapeutic alternatives for patients with PHPT or SNPCs; they may have limited usefulness in patients with SHPT.

• Journal of the Korean Society of Radiology
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• v.85 no.3
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• pp.618-630
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• 2024

Purpose To compare the efficacy and safety of radiofrequency ablation (RFA) and ethanol ablation (EA) followed by RFA in treating mixed cystic and solid thyroid nodules. Materials and Methods We included 243 nodules from 243 patients who underwent RFA for mixed cystic and solid benign nodules. The nodules were divided into two groups (RFA alone and EA + RFA). We evaluated volume reduction rate (VRR), therapeutic success rate, improvement in symptomatic and cosmetic issues, complications, and adverse effects. Results The RFA group included 204 patients, and the EA + RFA group included 39 patients. The long-term success rates in the RFA only and EA + RFA groups were 90.2% and 97.4%, respectively. The mean VRR at the last follow-up in the RFA and EA + RFA groups were 81.6% and 87.2%, respectively. Therapeutic results were similar in both groups at the last followup. Cosmetic and symptomatic problems markedly improved in both groups. No major complications were observed. Conclusion Both RFA alone and EA + RA are safe and effective methods for treating mixed cystic and solid thyroid nodules, although EA + RFA is slightly more effective.

• Proceedings of the IEEK Conference
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• 2003.11c
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• pp.24-27
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• 2003

Radiofrequency ablation (RFA) as one of the microwave hyperthermia is becoming the treatment of choice for small but inoperable tumors of the liver. In this paper, we designed the applicator composed of semi-rigid coaxial cable antenna with a ring slot for RFA. To optimize the maximum output of radiation with omni direction at 2450 ㎒, we simulated the applicator using Electromagnetic simulation program and analyzed the return loss and the electric field E$\_$tot/ at the near-field region between the simulation results and measurement results. As a result, we obtained the return loss of -29.786 dB at 2450 ㎒ when the applicator was placed between two blocks of a pig's liver, and the measurement results agreed with the simulation results well. Therefore, this applicator using semi-rigid coaxial cable antenna with a ring slot can be used very usefully as the applicator for RFA.

• Wind and Structures
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• v.35 no.5
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• pp.323-336
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• 2022

This study investigates the applicability of the direct identification of flutter derivatives in the time domain using Rational Function Approximation (RFA), where the extraction procedure requires either a combination of at least two wind speeds or one wind speed. In the frequency domain, flutter derivatives are identified at every wind speed. The ease of identifying flutter derivatives in the time domain creates a paradox because flutter derivative patterns sometimes change in higher-order polynomials. The first step involves a numerical study of RFA extractions for different deck shapes from existing bridges to verify the accurate wind speed combination for the extraction. The second step involves validating numerical simulation results through a wind tunnel experiment using the forced vibration method in one degree of freedom. The findings of the RFA extraction are compared to those obtained using the analytical solution. The numerical study and the wind tunnel experiment results are in good agreement. The results show that the evolution pattern of flutter derivatives determines the accuracy of the direct identification of RFA.

• Journal of the Korean Society of Radiology
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• v.84 no.5
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• pp.985-998
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• 2023

Radiofrequency ablation (RFA) has been a representative, non-surgical treatment for benign thyroid nodules that cause cosmetic problems or compression symptoms. The procedure of RFA should be performed effectively and safely. This review discusses the patient selection, pre-procedure evaluation and planning, principles, devices, techniques, and complications with reference to the guidelines and research on thyroid RFA. In particular, this review will devote to introduce RFA techniques and to provide practical help in the implementation of this procedure.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.6
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• pp.745-750
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• 2005

Statement of problem. Resonance frequency analysis has been increasingly served as a non-invasive and objective method for clinical monitoring of implant stability. Many clinical studies must be required for standardized data using RFA. Purpose. This study was performed to evaluate RFA value changes in two anodized implant groups. Material and method. Among a total of 24 implants, twelve screw shaped implants as a test group (H2-R8.5) were manufactured, which had a pitch-height of 0.4 mm, an outer diameter of 4.3 mm, a length of 8.5 mm, and external hexa-headed, were turned from 5 mm rods of commercially pure titanium (ASTM Grade IV, Warantec Co., Seoul, Korea), and another twelve implants as a control group were $Br{\aa}nemark$ Ti-Unite MK4 (diameter 4.0 mm, length 8.5 mm). Each group was installed in tibia of rabbit. Two implants were placed in each tibia (four implants per rabbit). Test two implants were inserted in right side and control two in left side. ISQ values were measured using $Osstell^{TM}$ (Integration Diagnostics Ltd. Sweden) during fixture installation, and 12 weeks later and evaluated the RFA changes. Results. Mean and SD of baseline ISQ values of test group were $75.0{\pm}3.4$ and $68.7{\pm}8.1$ for control group. Mean and SO of ISQ values 12 weeks after implant insertion were $73.2{\pm}4.7$ for test group and $72.6{\pm}3.9$ for control group. There were no statistically significant differences between groups in ISQ values after 3 months (P>0.05). From the data, RFA gains after 3 months were calculated, and there was statistically significant difference between groups (P<0.05). Conclusion. Although there were RFA changes between groups, implant stability after experimental period shows alike tendency and good bone responses.

• Asian Pacific Journal of Cancer Prevention
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• v.16 no.18
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• pp.8559-8561
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• 2016

Purpose: To evaluate efficacy of radiofrequency ablation (RFA) in treating colorectal cancer patients with liver metastases. Methods: During January 2010 to April 2012, 56 colorectal cancer patients with liver metastases underwent RFA. CT scans were obtained one month after RFA for all patients to evaluate tumor response. (CR+PR+SD)/n was used to count the disease control rates (DCR). Survival data of 1, 2 and 3 years were obtained from follow up. Results: Patients were followed for 10 to 40 months after RFA (mean time, $25{\pm}10months$). Median survival time was 27 months. The 1, 2, 3 year survival rate were 80.4%, 71.4%, 41%, 1 % respectively. 3-year survival time for patients with CR or PR after RFA was 68.8% and 4.3% respectively, the difference was statistically significant. The number of CR, PR, SD and PD in our study was 13, 23, 11 and 9 respectively. Conclusions: RFA could be an effective method for treating colorectal cancer patients with liver metastases, and prolong survival time, especially for metastatic lesions less than or equal to 3 cm. But this result should be confirmed by randomized controlled studies.

• Investigative Magnetic Resonance Imaging
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• v.20 no.4
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• pp.231-240
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• 2016

Purpose: To determine whether liver stiffness (LS) measured by magnetic resonance elastography (MRE) can predict the outcome of radiofrequency ablation (RFA) in hepatocellular carcinoma (HCC) patients. Materials and Methods: A total of 107 patients with Child-Pugh class A liver function who were treated with RFA for single HCC and who had undergone a gradient-echo MRE within 6 months before RFA were included. We evaluated the relationship between the LS values and the ablation volume, local tumor progression (LTP), and intrahepatic distant recurrence (IDR). We also constructed receiver operating characteristic (ROC) curves to examine the role of LS in predicting liver function deterioration, which was defined as an increase of Child-Pugh score by one point or more at 1 year after RFA. Results: There was no significant correlation between LS and ablation volume, and neither time to LTP nor IDR was associated with LS. Among the 66 patients who did not have recurrence 1 year after RFA, 5 patients (7.6%) developed liver function deterioration. A high LS value was significantly associated with development of liver function deterioration after RFA and the area under the ROC curve was 0.764 (95% CI 0.598-0.929, P = 0.003). Conclusion: LS measured by MRE could not predict ablation volume and tumor recurrence. However, high LS values were significantly associated with development of liver function deterioration.

• Korean Journal of Radiology
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• v.25 no.3
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• pp.301-313
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• 2024

Objective: The current body of evidence lacks clarity regarding the comparative efficacy and safety of radiofrequency ablation (RFA) and microwave ablation (MWA) as minimally invasive treatments for benign thyroid nodules. The primary objective of this study is to clarify these concerns. Materials and Methods: A comprehensive search was conducted using the Cochrane Library, Scopus, Europe PMC, and Medline databases until October 10th, 2023, using a combination of relevant keywords. This study incorporated literature that compared RFA and MWA for benign thyroid nodules. The primary outcome was the volume reduction ratio (VRR) from baseline to follow-up. Secondary outcomes were symptom score, cosmetic score, ablation time, major complications rate, hemorrhage, hoarseness, skin burn, cough, and sympathetic nerve injury. We used Risk of Bias in Non-randomized Studies - of Interventions (ROBINS-I) tool to assess the risk of bias in the included studies. We employed random effects models to analyze the standardized mean difference (SMD) and odds ratio for the presentation of outcomes. Results: Nine studies with 2707 nodules were included. The results of our meta-analysis indicated similar efficacy between RFA and MWA in terms of VRR during the 1 (SMD 0.06; 95% confidence interval [CI]: -0.13 to 0.26; P = 0.52) and 3 (SMD 0.11; 95% CI: -0.03 to 0.25; P = 0.12) months of follow-up. VRR was significantly higher in RFA than in MWA at the 6 (SMD 0.25; 95% CI: 0.06-0.43; P = 0.008) and 12 month of follow-up (SMD 0.38; 95% CI: 0.17 to 0.59; P < 0.001). There were no significant differences between RFA and MWA in symptom scores, cosmetic scores, or the incidence of complications, including hemorrhage, hoarseness, skin burn, cough, and sympathetic nerve injury. Conclusion: RFA showed a higher VRR than MWA at 6 and 12-month follow-ups, with a comparable safety profile.