• Korean Journal of Radiology
• /
• v.20 no.4
• /
• pp.580-588
• /
• 2019

Objective: To evaluate the impact of energy and access methods on extrahepatic tumor spreading and the ablation zone in an ex vivo subcapsular tumor mimic model with a risk of extrahepatic tumor spreading. Materials and Methods: Forty-two tumor-mimics were created in bovine liver blocks by injecting a mixture of iodine contrast material just below the liver capsule. Radiofrequency (RF) ablations were performed using an electrode placed parallel or perpendicular to hepatic surface through the tumor mimic with low- and high-power protocols (groups 1 and 2, respectively). Computed tomography (CT) scans were performed before and after ablation. The presence of contrast leak on the hepatic surface on CT, size of ablation zone, and timing of the first roll-off and popping sound were compared between the groups. Results: With parallel access, one contrast leak in group 1 (1/10, 10%) and nine in group 2 (9/10, 90%) (p < 0.001) were identified on post-ablation CT. With perpendicular access, six contrast leaks were identified in each group (6/11, 54.5%). The first roll-off and popping sound were significantly delayed in group 1 irrespective of the access method (p = 0.002). No statistical difference in the size of the ablation zone of the liver specimen was observed between the two groups (p = 0.247). Conclusion: Low-power RF ablation with parallel access is proposed to be effective and safe from extrahepatic tumor spreading in RF ablation of a solid hepatic tumor in the subcapsular location. Perpendicular placement of an electrode to the capsule is associated with a risk of extrahepatic tumor spreading regardless of the power applied.

• Journal of the Korean institute of surface engineering
• /
• v.55 no.6
• /
• pp.308-318
• /
• 2022

The surface modification and treatment using thermal plasma were reviewed in academic fields. In general, thermal plasma is generated by direct current (DC) and radiofrequency (RF) power sources. Thermal spray coating, a typical commercial process using thermal plasma, is performed by DC thermal plasma, whereas other promising surface modifications have been reported and developed using RF thermal plasma. Beyond the thermal spray coating, physical and chemical surface modifications were attempted widely. Superhydrophobic surface treatment has a very high industrial demand particularly. Besides, RF thermal plasma system for large-area film surface treatment is being developed. Thermal plasma is especially suitable for the surface modification of low-dimensional nanomaterial (e.g., nanotubes) by utilizing high temperature and rapid quenching. It is able to synthesize and modify nanomaterials simultaneously in a one-pot process.

• Investigative Magnetic Resonance Imaging
• /
• v.16 no.2
• /
• pp.103-114
• /
• 2012

Purpose : In an attempt to further improve the radiofrequency (RF) magnetic ($B_1$) field strength in temporomandibular joint (TMJ) imaging, a 4-channel spiral-loop coil array with RF circuitry was designed and compared with a 4-channel single-loop coil array in terms of $B_1$ field, RF transmit (${B_1}^+$), signal-to-noise ratio (SNR), and applicability to TMJ imaging in 7T MRI. Materials and Methods: The single- and 4-channel spiral-loop coil arrays were constructed based on the electromagnetic (EM) simulation for the investigation of $B_1$ field. To evaluate the computer simulation results, the $B_1$ field and ${B_1}^+$ maps were measured in 7T. Results: In the EM simulation result and MRI study at 7T, the 4-channel spiral-loop coil array found a superior $B_1$ performance and a higher ${B_1}^+$ profile inside the human head as well as a slightly better SNR than the 4-channel single-loop coil array. Conclusion: Although $B_1$ fields are produced under the influence of the dielectric properties of the subject rather than the coil configuration alone at 7T, each RF coil exhibited not only special but also specific characteristics that could make it suited for specific application such as TMJ imaging.

• The Korean Journal of Pain
• /
• v.9 no.1
• /
• pp.200-205
• /
• 1996

Radiofrequency thermocoagulation(RF) techniques are safe and effective methods as compared to neurodestructive procedure. Other advantages are: ability to perform RF lesions under local or sedative anesthesia, rapid recovery period, low incidence of morbidity and mortality, ability to repeat RF lesions, and leaves no significant scarring. We performed C2 ganglionotomy by RF lesion generator on a patient, suffering post-traumatic occipital neuralgia, as the patient did not respond to conservative therapies such as: trigger point injection, TENS, cryotherapy and stretch, occipital nerve block, C2 ganglion block. Prognostic nerve block was performed usng local anesthetics. Excellent effect was conformed before C2 ganglionotomy. This procedure was performed under fluoroscopy. Type RCK-2A Rosomoff Cordotomy kit was used to stabilize the head and neck. Postoperatively, the patient was free of occipital pain and head motions no longer triggered pain. To date, the patient remains symptom free except for some cervical discomfort.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.15 no.6
• /
• pp.3799-3804
• /
• 2014

In sea water, microalgae are exposed to a range of critical environmental conditions. Microalgae are protected from UV-A radiation due to the presence of mycosporine like amino acids(MAAs). Owing to the UV-A absorption properties of MAAs, they are used widely as a UV protecting ingredient in cosmetics. Therefore, there is a need to increase the production yield of MAAs. This study investigated the production yield of MAAs in transformed microalgae by radiofrequency(RF) exposure. Initially, the Glut-1 gene was transformed to Chlamydomonas hedleyi microalgae as a glucose transporter. The biomass was enhanced after Glut-1 gene transformation. In addition, the MAAs production yield was increased during large scale production in bioreactors due to the RF treatment. Therefore, purified extracts of MAAs can be used as a sun block material in the cosmetic industrial field.

• Korean Journal of Radiology
• /
• v.21 no.9
• /
• pp.1077-1086
• /
• 2020

Objective: To evaluate the effect of perfluorobutane microbubbles (Sonazoid^®, GE Healthcare) on steam popping during radiofrequency (RF) ablation for treating hepatocellular carcinoma (HCC), and to assess whether popping affects treatment outcomes. Materials and Methods: The institutional review board approved this retrospective study, which included 90 consecutive patients with single HCC, who received percutaneous RF ablation as the first-line treatment. The patients were divided into two groups, based on the presence or absence of the popping phenomenon, which was defined as an audible sound with a simultaneous sudden explosion within the ablation zone as detected via ultrasonography during the procedure. The factors contributing to the popping phenomenon were identified using multivariable logistic regression analysis. Local tumor progression (LTP) and disease-free survival (DFS) were assessed using the Kaplan-Meier method with the log-rank test for performing comparisons between the two groups. Results: The overall incidence of the popping phenomenon was 25.8% (24/93). Sonazoid^® was used in 1 patient (4.2%) in the popping group (n = 24), while it was used in 15 patients (21.7%) in the non-popping group (n = 69). Multivariable analysis revealed that the use of Sonazoid^® was the only significant factor for absence of the popping phenomenon (odds ratio = 0.10, p = 0.048). There were no significant differences in cumulative LTP and DFS between the two groups (p = 0.479 and p = 0.424, respectively). Conclusion: The use of Sonazoid^® has a suppressive effect on the popping phenomenon during RF ablation in patients with HCC. However, the presence of the popping phenomenon may not affect clinical outcomes.

• Journal of the Korean Society of Radiology
• /
• v.11 no.1
• /
• pp.49-54
• /
• 2017

As the Radiofrequency(RF) increases with the magnetic field strength, the wavelength of the RF excitation field becomes smaller, which leads to more the thermal effect in the human-body placed in the electric field. MRI scanner used was GE signa 1.5T, HDx 3.0T and Philips 3.0T with same routine clinical sequence protocol. Therefore temperature was measured before and after each scan. Taken the temperatures in the ear with ear infra-red type thermometer(Braun co). 3.0T were temperature increases more than $0.15^{\circ}C$ and GE 3.0T MRI equipment about $0.14^{\circ}C$ higher than the Philips 3.0T MRI(p<0.012). Psychogenic status was investigated by the survey respondents about their status can not just answer therefore, a little different from the expected. In our study of Thermal effect of clinical MRI with clinical protocol sequence, we found that the 3.0T in the body-temperature rise was greater than the 1.5T. Therefore, in clinical 3.0T examine the dangerous situation caused by the temperature rise occurred (burns, impaired thermoregulatory mechanism in patients with high-temperature damage, exhaustion occurs due to excessive sweating), not to appear the more watched the patient's condition with procedure.

• The Korean Journal of Physiology and Pharmacology
• /
• v.21 no.2
• /
• pp.179-188
• /
• 2017

With the explosive increase in exposure to radiofrequency electromagnetic fields (RF-EMF) emitted by mobile phones, public concerns have grown over the last few decades with regard to the potential effects of EMF exposure on the nervous system in the brain. Many researchers have suggested that RF-EMFs can effect diverse neuronal alterations in the brain, thereby affecting neuronal functions as well as behavior. Previously, we showed that long-term exposure to 835 MHz RF-EMF induces autophagy in the mice brain. In this study, we explore whether shortterm exposure to RF-EMF leads to the autophagy pathway in the cerebral cortex and brainstem at 835 MHz with a specific absorption rate (SAR) of 4.0 W/kg for 4 weeks. Increased levels of autophagy genes and proteins such as LC3B-II and Beclin1 were demonstrated and the accumulation of autophagosomes and autolysosomes was observed in cortical neurons whereas apoptosis pathways were up-regulated in the brainstem but not in the cortex following 4 weeks of RF exposure. Taken together, the present study indicates that monthly exposure to RF-EMF induces autophagy in the cerebral cortex and suggests that autophagic degradation in cortical neurons against a stress of 835 MHz RF during 4 weeks could correspond to adaptation to the RF stress environment. However, activation of apoptosis rather than autophagy in the brainstem is suggesting the differential responses to the RF-EMF stresses in the brain system.

• Journal of Sensor Science and Technology
• /
• v.21 no.2
• /
• pp.103-108
• /
• 2012

Radiofrequency(RF) signal is a key medium to the most of the present wireless communication devices including RF identification devices(RFID) and smart sensors. However, the most critical barrier to overcome in RFID application is in the failure rate in detection. The most notable improvement in the detection was from the introduction of EPC Class1 Gen2 protocol, but the fundamental problems in the physical properties of the RF signal drew less attention. In this work, we focused on the physical properties of the RF signal in order to understand the failure rate by noting the existence of the ground planes and noise sources in the real environment. By using the mathematical computation software, Maple, we simulated the distribution of the electromagnetic field from a dipole antenna when ground planes exist. Calculations showed that the dark area can be formed by interference. We also constructed a test system to measure the failure rate in the detection of a RFID transponder. The test system was composed of a fixed RFID reader and an EPC Class1 Gen2 transponder which was attached to a scanner to sweep in the x-y plane. Labview software was used to control the x-y scanner and to acquire data. Tests in the laboratory environment showed that the dark area can be as much as 43 %. One who wants to use RFID and smart sensors should carefully consider the extent of the dark area.

• Clinical and Experimental Reproductive Medicine
• /
• v.35 no.1
• /
• pp.77-82
• /
• 2008

Objective: This study was performed to investigate the efficacy and safety of radiofrequency (RF) myolysis under transvaginal ultrasound guidance. Methods: Transvaginal RF myolysis had been performed in one hundred nine women with uterine leiomyoma at Chung-Ang University hospital between Dec. 2004 and Mar. 2007. All patients, mean aged $42.8{\pm}5.8$ years, desired their uterine conservation. Patients underwent physical examination, transvaginal pelvic ultrasound for measurement of the lesions preoperatively. Follow up was done at 1 week, 1 month, 3 months, 6 months after RF myolysis by same physician and measurement of size and volume of myoma and improvement of myoma specific symptoms such as menorrhagia and dysmenorrhea were checked at each visit. Results: The mean maximal diameter of myomas treated by RF myolysis was $6.1{\pm}0.5\;cm$ and average time of the procedure was $16.3{\pm}8.5$ minutes. A significant decrease of myoma size and volume was observed at 1 month after myolysis. Mean reduction in maximal diameter was $29.9{\pm}4.8%$ at 1 week (p<0.001), $41.5{\pm}1.5%$ at 1 month (p=0.05), $46.2{\pm}3.9%$ at 3 months (p=0.003), $54.6{\pm}6.1%$ at 6 months (p<0.001) after RF myolysis respectively. Mean reduction in volume was $44.4{\pm}8.3%$ (p=0.001), $68.1{\pm}4.2%$ (p=0.035), 73.9$73.9{\pm}4.8%$ (p=0.042), $84.5{\pm}5.1%$ (p<0.001) at the same follow up period respectively. Significant improvement of symptom was observed at 3 months after RF myolysis. Transient low abdominal pain and prolonged vaginal bleeding were detected in 3 patients each but spontaneously resolved and no serious complication has been noticed or found. Conclusion: This study shows transvaginal RF myolysis could be a safe and effective method to treat uterine leiomyoma, allowing uterine conservation with significant volume reduction and rapid return to normal activity.