Simultaneous Radiofrequency Research Articles

Increased Ablation Zones Using a Cryo-Based Internally Cooled Bipolar RF Applicator in Ex Vivo Bovine Liver

To evaluate the feasibility of ex vivo ablation implementing a cryo-based internally cooled bipolar radiofrequency (RF) applicator and to determine the influence of power and gas pressure on the size and shape of the resulting ablation zones. Two hundred twenty-five ablations were performed using a custom-built internally CO2-cooled bipolar cryo RF applicator in ex vivo bovine livers. The active tip of the applicator was 55 mm long. RF power (32-50 watts) and gas pressure of cooling medium (500-600 psi) were varied independently. Power was applied in continuous mode. Control group experiments were carried out solely using the RF function at 32, 40, and 50 watts. Ablation duration was 15 minutes for all applications. Experiments were repeated 5 times for all parameter combinations. Short and long axes of the induced white ablation zone were macroscopically assessed. The ablation zone was referred to as homogeneous if complete ablation was observed without spots of untreated tissue. The short axis diameters for the simultaneous application of cryo and RF function were analyzed using a multiple linear regression analysis. An unpaired Mann-Whitney U test was used to analyze the differences between the short axes with RF alone and RF using cryo cooling. All ablation zones were homogeneous. Using simultaneous RF ablation function and gas cooling with a single applicator, the long axes of the ablation zones ranged between 42 +/- 2 mm (mean +/- SD) and 59 +/- 5 mm, the short axes between 24 +/- 1 and 44 +/- 1 mm, depending on the parameter combination. At a stable gas pressure level, short axes increased with rising power levels and decreased after reaching a maximum. The maxima of the short axis increased with higher gas pressure levels and were shifted to higher power values. Optimal parameter settings were 46 to 50 watts and 600 psi gas pressure, resulting in a short axis of 44 +/- 1 mm. Short axis weakly correlated with gas pressure (r2 = 0.10) and power (r2 = 0.34) alone, whereas the correlation was r2 = 0.76 for the combined factors. Without cooling, short axis diameters were significantly shorter (P < 0.05), ranging between 13 +/- 2 mm at 50 watts and 15 +/- 2 mm at 32 watts. The results of this initial ex vivo study show that the combined cryo RF ablation device allows for large ablation volumes using a single needle, which is superior to RF ablation alone.

Laparoscopic colorectal resection combined with simultaneous radiofrequency ablation for liver metastases

Objective To assess the clinical value of laparoscopic colorectal resection combined with simultaneous radiofrequency ablation for liver metastases.Methods Twenty-two patients with colorectal cancer and synchronous liver metastases were treated by laparoscopie colorectal resection and simultaneous radiofrequency ablation(RFA)in Third People's Hospital of Chengdu from December 2001 to July 2006.Areas of colliquative necrosis were detected by contrast-enhanced computed tomography postoperatively.The outcomes were analyzed by chi-square test.Results Of all patients,8 had muhiple liver metastases,16 had complications.Thirty-one liver metastases were treated by RFA,and no complication oecurred.The mean postoperative hospital stay was(14±5)days,and there was no perioperative death.Five of the 22 patients were identified as incomplete ablation of the tumor,and the RFA was reperformed.The recurrence of liver metastases in the RFA necrotic zone was observed in 4 patients,and RFA was reperformed on 2 of them.Six patients died,and 2 of them died of liver metastases recurrence in the RFA necrotic zone.The recurrence rate of liver metastases and mortality was 18%(4/22)and 27%(6/22),respectively.The recurrence rate of patients with the diameter of the metastatic lession≥2.0 cm was significantly higher than those with the diameter of the metastatic lession＜2.0 cm(x2=5.867,P＜0.05).Conclusions Laparoseopie colorectal resection combined with simultaneous RFA provide a curative opportunity for colorectal cancer patients who are old and have multiple liver metastases,complications,poor tolerance of operation,and for patients whose tumors are difficult to resect. Key words: Colorectal neoplasms; Liver metastasis; Laparoscopy; Catheter ablation,radiofrequeney DOI:10.3760/cma.j.issn.1673-9752.2009.01.011

Combined hepatectomy and radiofrequency ablation for multifocal hepatocellular carcinoma: a case report

IntroductionAt the present time, the best possible choice for the local management of a multifocal hepatocellular carcinoma (HCC) developing on liver cirrhosis is multimodal treatment of the disease. Combined approach based on simultaneous radiofrequency ablation (RFA) together with limited surgical resection represents a valid choice of treatment.Case presentationA 75-year-old white female patient affected of HCV-associated cirrhosis in Child-Pugh’s functional class A5, developed a bifocal HCC. The patient had undergone a limited surgical resection together with simultaneous RFA, without intraoperative and postoperative surgical complications. At 36 months after surgery, still shows no sign of disease relapse.ConclusionThis strategy directed at the management of multifocal HCC, may prove more useful for the reduction of surgical risk and post-operative progression of the liver cirrhosis than large-scale hepatectomy, since it presents no peri-operative mortality and a complication rate of less than 10%.

Validation of fast MR thermometry at 1.5 T with gradient‐echo echo planar imaging sequences: phantom and clinical feasibility studies

The purpose of this work was to validate in phantom studies and demonstrate the clinical feasibility of MR proton resonance frequency thermometry at 1.5 T with segmented gradient-echo echo planar imaging (GRE-EPI) sequences during liver tumour radiofrequency (RF) ablation. Classical GRE acquisitions and segmented GRE-EPI acquisitions were performed at 1.5 T during simultaneous RF heating with an MR-compatible RF electrode placed in an agar gel phantom. Temperature increments were calculated and compared with four optical temperature probe measurements using Bland- Altman analysis. In a preliminary clinical feasibility study, the rapid GRE-EPI sequence (echo train length = 13) was used for MR temperature monitoring of RF ablation of liver tumours in three patient procedures. For phantom experiments, the Bland-Altman mean of differences between MR and optical probe temperature measurements was <0.4 degrees C, and the 95% limits of agreement value was <1.4 degrees C. For the in vivo studies, respiratory-triggered GRE-EPI acquisitions yielded a temperature accuracy of 1.3 +/- 0.4 degrees C (acquisition time = 0.6 s/image, spatial coverage of three slices/respiratory cycle). MR proton resonance frequency thermometry at 1.5 T yields precise and accurate measurements of temperature increment with both classical GRE and rapid GRE-EPI sequences. Rapid GRE-EPI sequences minimize intra-scan motion effects and can be used for MR thermometry during RF ablation in moving organs.

A Novel Hybrid Transcatheter Ablation System That Combines Radiofrequency and Cryoenergy

Radiofrequency (RF) and cryoenergy are largely considered independent modalities for the transcatheter ablation of cardiac arrhythmias. There are numerous theoretical advantages to engineering a system capable of delivering both energy forms. We designed a hybrid steerable catheter capable of delivering RF and cryoenergy independently, sequentially, and simultaneously. The novel catheter system was tested pre-clinically by creating a total of 180 ablation lesions in 20 mongrel dogs. Right atrial and right and left ventricular sites were preselected by a randomized factorial design devised to compare sequential and simultaneous RF and cryoenergy applications to standard RF, irrigated RF, and standard cryoablation. A steerable 4-mm electrode-tip hybrid catheter ("Fire and Ice") was created by modifying a 7 F cryocatheter (Freezor, CryoCath Technologies, Montreal, Canada). RF energy was injected via a copper wire, thermocouples were isolated to reduce RF interference, and 100 KHz band pass filters and RF chokes were added. Sequential low-dose RF (20 W, 60 seconds) preceding or following cryoablation resulted in larger lesions (P = 0.0010). The addition of RF energy did, however, produce more thrombus than cryoenergy alone, with clot detected on 82.4% versus 12.1% of ablation lesions, P < 0.0001. Simultaneously applying the two energy modalities (45 W, 10 or 30 degrees C, 60 seconds) created more voluminous lesions than standard RF ablation (median 288.1 vs 126.1 mm(3), P = 0.0333) of similar dimension to irrigated RF ablation. A versatile catheter system was fashioned capable of creating standard cryoablation lesions, standard RF lesions, and simultaneous lesions of similar dimension to irrigated RF.

Treatment of Lymphangioma Circumscriptum with Combined Radiofrequency Current and 900 nm Diode Laser

Laser treatment of lymphangioma circumscriptum is a major challenge because of the persistent nature of the disease and the large variations in lesion size, depth, and anatomic location. To determine the safety and effectiveness of electro-optical synergy, a new technology that combines a 900 nm diode laser with radiofrequency current, for the treatment of lymphangioma circumscriptum. Six patients with Fitzpatrick skin types II to IV were treated for lymphangioma circumscriptum with 1 to 3 sessions of simultaneous radiofrequency energy (60-80 J/cm3) and optical diode laser energy (fluence 90-100 J/cm2). Lesion clearance was evaluated by three specialists on the basis of digital photographs taken before the first treatment and 1 and 2 months after the last treatment. Results were rated as "excellent" in four patients and "good" in two patients. Transient swelling, erythema, and pain were present in all patients, and ulcers and scarring in two patients. The combination of laser light and radiofrequency energy is effective and relatively safe for the treatment of lymphangioma circumscriptum. It provides additional heating of the blood vesicles without increasing the laser intensity and allows the clinician to treat the clear lymphatic component, which lacks a specific optical chromophore. Side effects are tolerable.

Treatment of Lymphangioma Circumscriptum with Combined Radiofrequency Current and 900 nm Diode Laser

BACKGROUND Laser treatment of lymphangioma circumscriptum is a major challenge because of the persistent nature of the disease and the large variations in lesion size, depth, and anatomic location. OBJECTIVE To determine the safety and effectiveness of electro-optical synergy, a new technology that combines a 900 nm diode laser with radiofrequency current, for the treatment of lymphangioma circumscriptum. METHODS Six patients with Fitzpatrick skin types II to IV were treated for lymphangioma circumscriptum with 1 to 3 sessions of simultaneous radiofrequency energy (60–80 J/cm3) and optical diode laser energy (fluence 90–100 J/cm2). Lesion clearance was evaluated by three specialists on the basis of digital photographs taken before the first treatment and 1 and 2 months after the last treatment. RESULTS Results were rated as “excellent” in four patients and “good” in two patients. Transient swelling, erythema, and pain were present in all patients, and ulcers and scarring in two patients. CONCLUSION The combination of laser light and radiofrequency energy is effective and relatively safe for the treatment of lymphangioma circumscriptum. It provides additional heating of the blood vesicles without increasing the laser intensity and allows the clinician to treat the clear lymphatic component, which lacks a specific optical chromophore. Side effects are tolerable.

Treatment of Facial Venous Malformations with Combined Radiofrequency Current and 900 nm Diode Laser

Laser treatment of venous malformations is a major challenge because of the large variations in skin pigmentation, anatomic location, and vessel size and depth. To determine the safety and effectiveness of electro-optical synergy, a new technology that combines the 900 nm diode laser with radiofrequency current for the treatment of facial venous malformation. Fourteen patients with Fitzpatrick skin types II to IV were treated for facial venous malformations with simultaneous radiofrequency energy (60-80 J/cm3) and optical diode laser energy (fluence 80-100 J/cm2) in one to three sessions. All lesions measured less than 100 cm2. Lesion clearance was evaluated by three specialists on the basis of digital photographs taken before the first treatment and 1 and 2 months after the last treatment. Thirteen patients showed a complete response and one patient a partial response. The results were rated excellent in the 13 patients and good in one patient. Transient swelling, erythema, and pain were present in all patients, with permanent scarring in only one patient. The combination of laser light and radiofrequency energy is effective and safe for the treatment of facial venous malformations. It provides additional heating of the vessels without increasing laser intensity. The side effects are minimal.

In vivo porcine liver radiofrequency ablation with simultaneous MR temperature imaging

To demonstrate in vivo MR-guided temperature mapping during radiofrequency (RF) ablation of the liver with a commercially available RF generator modified to allow simultaneous RF treatment and MRI. A commercial RF generator was modified using passive filtering to allow the continuous application of the treatment current during MRI studies. A total of six ablations were performed with the device in vivo in three porcine livers, and imaging was concurrently performed using one of two different temperature mapping strategies. MR images acquired during RF ablation demonstrated no noticeable interference from the RF ablation device, which was operated at clinically relevant power levels. Temperature maps showed areas of heating that were consistent with the dimensions of the RF ablation probe, with some asymmetry (likely depending on the orientation of the probe and heat propagation effects), and some differences in heating-spot area stability depending on the specific temperature mapping strategy used. Lesions were visualized on post-ablation imaging and sectioning. The feasibility of performing RF ablation with a modified commercial RF generator simultaneously with MRI was demonstrated. Interference-free MR temperature maps were produced with both variable respiratory motion and mechanical ventilation, and showed the extent of heating as the ablation progressed.

Treatment of Facial Venous Malformations with Combined Radiofrequency Current and 900 nm Diode Laser

Background Laser treatment of venous malformations is a major challenge because of the large variations in skin pigmentation, anatomic location, and vessel size and depth. Objective To determine the safety and effectiveness of electro-optical synergy, a new technology that combines the 900 nm diode laser with radiofrequency current for the treatment of facial venous malformation. Methods Fourteen patients with Fitzpatrick skin types II to IV were treated for facial venous malformations with simultaneous radiofrequency energy (60–80 J/cm3) and optical diode laser energy (fluence 80–100 J/cm2) in one to three sessions. All lesions measured less than 100 cm2. Lesion clearance was evaluated by three specialists on the basis of digital photographs taken before the first treatment and 1 and 2 months after the last treatment. Results Thirteen patients showed a complete response and one patient a partial response. The results were rated excellent in the 13 patients and good in one patient. Transient swelling, erythema, and pain were present in all patients, with permanent scarring in only one patient. Conclusion The combination of laser light and radiofrequency energy is effective and safe for the treatment of facial venous malformations. It provides additional heating of the vessels without increasing laser intensity. The side effects are minimal.

Simultaneous radiofrequency (RF) heating and magnetic resonance (MR) thermal mapping using an intravascular MR imaging/RF heating system

Previous studies have confirmed the possibility of using an intravascular MR imaging guidewire (MRIG) as a heating source to enhance vascular gene transfection/expression. This motivated us to develop a new intravascular system that can perform MR imaging, radiofrequncy (RF) heating, and MR temperature monitoring simultaneously in an MR scanner. To validate this concept, a series of mathematical simulations of RF power loss along a 0.032-inch MRIG and RF energy spatial distribution were performed to determine the optimum RF heating frequency. Then, an RF generator/amplifier and a filter box were built. The possibility for simultaneous RF heating and MR thermal mapping of the system was confirmed in vitro using a phantom, and the obtained thermal mapping profile was compared with the simulated RF power distribution. Subsequently, the feasibility of simultaneous RF heating and temperature monitoring was successfully validated in vivo in the aorta of living rabbits. This MR imaging/RF heating system offers a potential tool for intravascular MR-mediated, RF-enhanced vascular gene therapy.

Effect of substrate temperature on the properties of Ti-doped ZnO films by simultaneous rf and dc magnetron sputtering

The Ti-doped ZnO (ZnO:Ti) films were prepared by simultaneous radio frequency (rf) magnetron sputtering of ZnO and dc magnetron sputtering of Ti. The Ti oxides increased with the decrease in substrate temperature. Therefore, by decreasing the substrate temperature, X-ray peaks shifted towards a lower diffraction angle. When the substrate temperature increased from 50 to 150 °C, the crystallinity increased obviously, but it decreased slightly at 200 °C. The morphologies of films were significantly affected by the substrate temperature. The electrons of ZnO:Ti films may be originated from the oxygen vacancies and Ti donors. The mean free path of carriers were much shorter, therefore grain boundary scattering could be ruled out. The variation in mobility could be due to the ionized impurity scattering and surface roughness. The resistivity of ZnO:Ti film at 100 °C has a minimum of 9.69 × 10 −3 Ω cm, which is mainly due to the higher product of carrier concentration and mobility. At various substrate temperatures, the visible transmission of ZnO:Ti films was high.

Large scale in vitro experiment system for 2 GHz exposure

A beam formed radiofrequency (RF) exposure-incubator employing a horn antenna, a dielectric lens, and a culture case in an anechoic chamber is developed for large scale in vitro studies. The combination of an open type RF exposure source and a culture case through which RF is transmitted realizes a uniform electric field (+/-1.5 dB) in a 300 x 300 mm area that accommodates 49 35 mm diameter culture dishes. This large culture dish area enables simultaneous RF exposure of a large number of cells or various cell lines. The RF exposure source operates at 2142.5 MHz corresponding to the middle frequency of the downlink band of the International Mobile Telecommunication 2000 (IMT-2000) cellular system. The dielectric lens, which has a gain of 7 dB, focuses RF energy in the direction of the culture case and provides a uniform electric field. The culture case is sealed and connected to the main unit for environmental control, located outside the anechoic chamber, via ducts. The temperature at the center of the tray, which contains the culture dishes in the culture room, is maintained at 37.0 +/- 0.2 degrees C by air circulation. In addition, the appropriate CO2 density and humidity supplied to the culture case realizes stable long-term culture conditions. Specific absorption rate (SAR) dosimetry is performed using an electric field measurement technique and the Finite Difference Time Domain (FDTD) calculation method. The results indicate that the mean SAR of the culture fluid at the bottom of the 49 (7 x 7 array) culture dishes used in the in vitro experiments is 0.175 W/kg for an antenna input power of 1 W and the standard deviation of the SAR distribution is 59%. When only 25 culture dishes (5 x 5 array) are evaluated, the mean SAR is 0.139 W/kg for the same antenna input power and the standard deviation of the SAR distribution is 47%. The proliferation of the H4 cell line in 72 h in a pair of RF exposure-incubators reveals that the culture conditions are equivalent to those of a common CO2 incubator.

Hybrid Radiofrequency and Cryoablation Device: Preliminary Results in an Animal Model

To determine whether the simultaneous application of combined bipolar radiofrequency (RF) ablation and cryoablation in a hybrid system produces larger ablation zones than RF or cryoablation alone. Multiple 15-minute ablations were performed in ex vivo bovine liver (n = 167) with a hybrid applicator system with RF ablation alone (0.3-0.7 A), cryoablation alone (3,500 psi, two freeze/thaw cycles), and combined RF/cryoablation (0.4-0.7 A, 1,000-3,500 psi) with use of a novel applicator consisting of two 2.5-cm active bipolar RF poles located on the same 18-gauge needle separated by two embedded cryoablation nozzles. Resultant coagulation diameters were compared with use of analysis of variance for more than three groups or Student t tests for two groups. Confirmation of the optimal parameters of combination RF/cryoablation was performed by reassessing a range of argon pressure (1,000-3,500 psi) and RF current (0.4-0.7 A) in in vivo porcine liver (n = 36). Arrays of two to four RF/cryoablation applicators were also assessed in ex vivo (n = 54) and in vivo (n = 12) liver. In ex vivo liver, simultaneous RF/cryoablation (0.6 A, 3,000 psi) produced 3.6 cm +/- 0.4 of short-axis coagulation. This was significantly larger than that achieved with optimal RF alone or cryoablation alone (1.5 cm +/- 0.3 and 1.6 cm +/- 0.3, respectively; F = 95; P < .01). The coagulation diameter with simultaneous combination RF/cryoablation was related in parabolic fashion to argon pressure and current with a multivariate r(2) of 0.68. For in vivo liver, optimal combination RF/cryoablation achieved 3.3 cm +/- 0.2 of coagulation, which was significantly larger than that achieved with RF alone (1.1 cm +/- 0.1; P < .01) or cryoablation alone (1.1 cm +/- 0.1 and 1.3 cm +/- 0.1; F = 203; P < .01). The greatest contiguous coagulation was achieved with multiple-applicator arrays. For ex vivo liver, short-axis coagulation measured 5.3 cm +/- 0.1, 6.4 cm +/- 0.1, and 7.6 cm +/- 0.1 for two-, three-, and four-applicator arrays, respectively. For in vivo liver, two-, three-, and four-applicator arrays produced 5.1 cm +/- 0.2, 5.8 cm +/- 0.5, and 7.0 cm +/- 0.5 of confluent coagulation, respectively. Simultaneous combination RF and cryoablation with use of a novel applicator design yielded significantly larger zones of coagulation than either modality alone. The large ablation diameters achieved warrant further investigation of the device.

A Frequency-Controlled Beam-Steering Array With Mixing Frequency Compensation for Multichannel Applications

A frequency-controlled beam-steering planar array with mixing frequency compensation is presented for cost-effective multichannel phased array applications. The new feed networks for frequency compensation not only operate in wide band but also ensure radio-frequency (RF) amplitude imbalance cancellation and progressive phase distribution. The parallel equal power dividers installed in both LO and intermediate-frequency (IF) feed networks provide uniform amplitude and phase distribution, while the fixed delay lines installed in the LO feed network exhibit precise phase progression, compared to a series feed structure. The LO power imbalance caused by the unequal delay line loss between elements is corrected by pumping each mixer into the LO saturation region, leading to linear IF-RF response. Thus, sidelobe degradation and pattern distortion caused by the RF amplitude imbalance, as well as the beam-steering error and beam squint caused by the phase errors of the delay lines, are removed. The proposed feed networks combined with quasi-Yagi antenna arrays and microwave monolithic integrated circuit mixers realize a broad bandwidth of more than 3 GHz in K band for multichannel wireless applications. The K band transmitter/receiver pair proposed in this paper successfully demonstrates two-channel simultaneous RF transmission and single channel 50-Mb/s data communication with 40/spl deg/ scanning. This simple, compact, yet cost-effective planar array ensures multichannel broadband wireless communications with beam-steering capability.

Multiple-beam fiber-optic beamformer with binary array of delay lines

A multibeam optical beamformer capable of controlling a phased-array antenna in receive/transmit mode is proposed. The processor can be programmed to sweep the antenna aperture following an independent angular sequence for each radio-frequency (RF) beam. A two-beam two-channel 3-bit version of the beamformer has been experimentally demonstrated. The optical beamformer processes two independent RF beams, for eight different angular directions, and it is based on a binary array of three delay lines. Each delay line is composed of four fiber Bragg gratings whose center wavelengths are channels 30 to 33 of the International Telecommunications Union (ITU) grid. Measurements are performed for both receive and transmit modes and for RF values between 0.5 and 1.5 GHz. We present beam-pattern results showing the squint-free performance of the beamformer within this frequency range. In the transmit mode, two RF beams are steered and characterized for a broadside target position. In the receive mode, the beamformer performance is characterized by detecting two simultaneous RF beams.

Fused hollow cathode cold atmospheric plasma source for gas treatment

A new type of the cold atmospheric plasma source for catalytic plasma treatment of gas is presented. The fused hollow cathode (FHC) source is based on simultaneous radio frequency (rf) generation of hollow cathode discharges in an integrated, open structure, with flowing gas. The resulting FHC discharge is very stable, homogeneous, luminous, volume filling, without streamers. The power consumption is very low, of the order of tenths of Watt per cm 2 of the electrode structure area. Experiments for the hollow electrode integrated open structure up to 20 cm 2 were performed. The concept of the source is extremely suitable for scaling up for different gas throughputs. The FHC source represents a new non-equilibrium atmospheric plasma source suitable for transformation of gas. Moreover, its design offers both catalytic reactions in the bulk of plasma and at solid surfaces composing the open structure.

Large-volume tissue ablation with radio frequency by using a clustered, internally cooled electrode technique: laboratory and clinical experience in liver metastases.

To evaluate whether coagulation necrosis achievable with radio-frequency (RF) ablation can be increased by using a cluster of closely spaced electrodes. RF was applied to ex vivo liver (n = 68), in vivo liver (n = 12), and in vivo muscle (n = 15) by using a cluster array of three separate internally cooled electrodes spaced 0.5 cm apart. The diameter of coagulation necrosis achieved with optimal RF deposition (1,400-2,150 peak mA) for 5-60 minutes of RF application was determined for electrode tip lengths of 1.5-3.0 cm and compared with that obtained by using a single electrode and otherwise similar technique. Ten patients with solitary intrahepatic colorectal metastases were also treated by using cluster electrode RF ablation. In ex vivo liver, simultaneous RF application to electrode clusters for 15, 30, and 45 minutes produced 4.7 cm +/- 0.1, 6.2 cm +/- 0.1, and 7.0 cm +/- 0.2 of coagulation necrosis, respectively. In in vivo liver and muscle, RF applied to electrode clusters for 12 minutes yielded 3.1 cm +/- 0.2 and 7.6 cm +/- 0.4 of coagulation, respectively. RF application to a single electrode produced maximal coagulation of 2.9 cm in ex vivo liver, 1.8 cm in in vivo liver, and 4.3 cm in muscle (P < .01, all tissues). In colorectal metastases, a single 12-15-minute application of RF to an electrode cluster induced 4.5-7.0 cm of coagulation necrosis. Simultaneous RF application to a cluster of three closely spaced internally cooled electrodes enables a larger volume of coagulation in ex vivo liver, in vivo tissues, and hepatic colorectal metastases than previously reported.

A method for simultaneous RF ablation and MRI.

Radiofrequency (RF) energy has many advantages in thermal tumor ablation protocols. With the recent development of open MRI systems, interventional MRI procedures, including thermal ablation, have become the focus of great research interest. However, the significant interference between RF generators and MR imagers has prevented simultaneous imaging and RF ablation and, until now, has limited the role of RF-based thermal therapy in interventional MRI. Here, a simple switching circuit designed with consideration of patient safety provides compatibility between open MRI systems and RF thermal lesion generators. The experimental results show that the switching circuit allows imaging during RF ablation and opens new opportunity for MR-guided thermal therapy.

Simultaneous multipolar radiofrequency ablation in the monopolar mode increases lesion size.

Delivery of radiofrequency (RF) energy from the distal tip of electrophysiology catheters produces lesions that may be too small to ablate arrhythmogenic sites during a single application of RF energy. To produce larger lesions, we delivered RF energy via a quadripolar catheter in which all four electrodes were connected in unipolar fashion. The catheter (Webster Labs) had a 4-mm tip, 2-mm ring electrodes, and 2-mm interelectrode distance. Lesion size was compared using RF energy delivered in a multipolar configuration with that delivered only to the distal tip using fresh bovine ventricular tissue. In vivo, RF lesions were made in dogs using the distal tip as well as all four poles of the same catheter inserted percutaneously. RF energy was delivered using a constant voltage at a frequency of 400 kHz. Preliminary experiments were conducted to determine the maximum power deliverable without coagulation using each electrode configuration. The use of simultaneous multipolar RF ablation produced significantly larger lesions both in vitro and in vivo. The length of the lesion was increased by a factor of approximately 2 in both the in vitro and in vivo experiments. There was a trend toward an increasing depth of the lesion by simultaneously applying RF energy to all four electrodes. Lesion width was significantly increased in the in vivo studies. We concluded that simultaneous multipolar delivery of RF energy produces larger lesions than can be obtained with delivery of RF energy to the distal tip alone. This technique may offer a means of increasing lesion size, leading to a decrease in the number of applications of RF energy necessary for ablation of arrhythmias.