Comparison of Wet Radiofrequency Ablation with Dry Radiofrequency Ablation and Radiofrequency Ablation Using Hypertonic Saline Preinjection: Ex Vivo Bovine Liver

Objective

We wished to compare the in-vitro efficiency of wet radiofrequency (RF) ablation with the efficiency of dry RF ablation and RF ablation with preinjection of NaCl solutions using excised bovine liver.

Materials and Methods

Radiofrequency was applied to excised bovine livers in a monopolar mode for 10 minutes using a 200 W generator and a perfused-cooled electrode with or without injection or slow infusion of NaCl solutions. After placing the perfused-cooled electrode in the explanted liver, 50 ablation zones were created with five different regimens: group A; standard dry RF ablation, group B; RF ablation with 11 mL of 5% NaCl solution preinjection, group C; RF ablation with infusion of 11 mL of 5% NaCl solution at a rate of 1 mL/min, group D; RFA with 6 mL of 36% NaCl solution preinjection, group E; RF ablation with infusion of 6 mL of 36% NaCl solution at a rate of 0.5 mL/min. In groups C and E, infusion of the NaCl solutions was started 1 min before RF ablation and then maintained during RF ablation (wet RF ablation). During RF ablation, we measured the tissue temperature at 15 mm from the electrode. The dimensions of the ablation zones and changes in impedance, current and liver temperature during RF ablation were then compared between the groups.

Results

With injection or infusion of NaCl solutions, the mean initial tissue impedance prior to RF ablation was significantly less in groups B, C, D, and E (43-75 Ω) than for group A (80 Ω) (p < 0.05). During RF ablation, the tissue impedance was well controlled in groups C and E, but it was often rapidly increased to more than 200 Ω in groups A and B. In group D, the impedance was well controlled in six of ten trials but it was increased in four trials (40%) 7 min after starting RF ablation. As consequences, the mean current was higher for groups C, D, and E than for the other groups: 401 ± 145 mA in group A, 287 ± 32 mA in group B, 1907 ± 96 mA in group C, 1649 ± 514 mA in group D, and 1968 ± 108 mA in group E (p < 0.05). In addition, the volumes of RF-induced coagulation necrosis were greater in groups C and E than in group D, which was greater than in groups A and B than in group E (p < 0.05); 14.3 ± 3.0 cm³ in group A; 12.4 ± 3.8 cm³ in group B; 80.9 ± 9.9 cm³ in group C; 45.3 ± 11.3 cm³ in group D and 81.6 ± 8.6 cm³ in group E. The tissue temperature measured at 15 mm from the electrode was higher in groups C, D and E than other groups (p < 0.05): 53 ± 12℃ in group A, 42 ± 2℃ in group B, 93 ± 8℃ in group C; 79 ± 12℃ in group D and 83 ± 8℃ in group E.

Conclusion

Wet RF ablation with 5% or 36% NaCl solutions shows better efficiency in creating a large ablation zone than does dry RF ablation or RF ablation with preinjection of NaCl solutions.     

Radiofrequency Ablation with a New Perfused-Cooled Electrode Using a Single Pump: An Experimental Study in Ex Vivo Bovine Liver

The purpose of this study was to assess the efficacy of a new perfused-cooled electrode that uses a single pump for creating a large ablation zone in explanted bovine liver. This was done by comparing with the radiofrequency (RF) ablation zones that were created with a monopolar cooled electrode to the RF ablation zones that were created by the new perfused-cooled electrode. We developed a new perfused-cooled electrode that uses a single pump by modifying a 17-gauge cooled electrode (Radionics) with a 2.5-cm outer metallic sheath (15-gauge) in order to allow use of the internal cooling water (5.85 % hypertonic saline) for the infused saline. Thirty ablation zones were created in explanted bovine livers (12-min ablation cycle; pulsed technique; 2000 mA, maximum) with three different regimens: group A, RF ablation with the 17-gauge cooled electrode; group B, RF ablation with the 15-gauge cooled electrode; group C, RF ablation with the perfused-cooled electrode. T2-weighted magnetic resonance (MR) imaging was obtained immediately after RF ablation for calculating volumes of the ablation zone. Following MR imaging, the ablation zones were excised and measured for transverse diameters and vertical diameters. The transverse diameter, vertical diameter, and the calculated volumes of the ablation zones on MR imaging were compared among the groups. Ablation zones created with the perfused-cooled electrode (group C) were significantly larger than those created with the 17-gauge cooled electrode (group A) and the 15-gauge cooled electrode (group B) according to the transverse diameter and vertical diameter on the gross specimens (p < 0.05): 3.6 ± 0.38 cm and 4.4 ± 0.20 cm in group A, 3.7 ± 0.08 cm and 4.6 ± 0.16 cm in group B, and 5.4 ± 0.65 cm and 6.0 ± 0.56 cm in group C, respectively. On the MR imaging, the calculated volumes of the ablation zones in group C were significantly larger than those in groups A and B (p < 0.05): 23.1 ± 8.7 cm³ in group A, 28.9 ± 5.7 cm³ in group B, and 80.0 ± 34 cm³ in group C, respectively. A new perfused-cooled electrode using a single pump could efficiently increase the size of the ablation zone in liver compared with a monopolar cooled electrode, and this was due to its simultaneous use of internal cooling and saline infusion.     

Monopolar Radiofrequency Ablation Using a Dual-Switching System and a Separable Clustered Electrode: Evaluation of the In Vivo Efficiency

Objective

To determine the in vivo efficiency of monopolar radiofrequency ablation (RFA) using a dual-switching (DS) system and a separable clustered (SC) electrode to create coagulation in swine liver.

Materials and Methods

Thirty-three ablation zones were created in nine pigs using a DS system and an SC electrode in the switching monopolar mode. The pigs were divided into two groups for two experiments: 1) preliminary experiments (n = 3) to identify the optimal inter-electrode distances (IEDs) for dual-switching monopolar (DSM)-RFA, and 2) main experiments (n = 6) to compare the in vivo efficiency of DSM-RFA with that of a single-switching monopolar (SSM)-RFA. RF energy was alternatively applied to one of the three electrodes (SSM-RFA) or concurrently applied to a pair of electrodes (DSM-RFA) for 12 minutes in in vivo porcine livers. The delivered RFA energy and the shapes and dimensions of the coagulation areas were compared between the two groups.

Results

No pig died during RFA. The ideal IEDs for creating round or oval coagulation area using the DSM-RFA were 2.0 and 2.5 cm. DSM-RFA allowed more efficient RF energy delivery than SSM-RFA at the given time (23.0 ± 4.0 kcal vs. 16.92 ± 2.0 kcal, respectively; p = 0.0005). DSM-RFA created a significantly larger coagulation volume than SSM-RFA (40.4 ± 16.4 cm³ vs. 20.8 ± 10.7 cm³; p < 0.001). Both groups showed similar circularity of the ablation zones (p = 0.29).

Conclusion

Dual-switching monopolar-radiofrequency ablation using an SC electrode is feasible and can create larger ablation zones than SSM-RFA as it allows more RF energy delivery at a given time.     

Saline-Enhanced Hepatic Radiofrequency Ablation Using a Perfused-Cooled Electrode: Comparison of Dual Probe Bipolar Mode with Monopolar and Single Probe Bipolar Modes

Objective

To determine whether saline-enhanced dual probe bipolar radiofrequency ablation (RFA) using perfused-cooled electrodes shows better in-vitro efficiency than monopolar or single probe bipolar RFA in creating larger coagulation necrosis.

Materials and Methods

RF was applied to excised bovine livers in both bipolar and monopolar modes using a 200W generator (CC-3; Radionics) and the perfused-cooled electrodes for 10 mins. After placing single or double perfused-cooled electrodes in the explanted liver, 30 ablation zones were created at three different regimens: group A; saline-enhanced monopolar RFA, group B; saline-enhanced single probe bipolar RFA, and group C; saline-enhanced dual probe bipolar RFA. During RFA, we measured the tissue temperature at 15mm from the electrode. The dimensions of the ablation zones and changes in the impedance currents and liver temperature during RFA were then compared between the groups.

Results

The mean current values were higher for monopolar mode (group A) than for the bipolar modes (groups B and C): 1550±25 mA in group A, 764±189 mA in group B and 819±98 mA in group C (p < 0.05). The volume of RF-induced coagulation necrosis was greater in group C than in the other groups: 27.6±2.9 cm³ in group A, 23.7±3.8 cm³ in group B, and 34.2±5.1 cm³ in group C (p < 0.05). However, there was no significant difference between the short-axis diameter of the coagulation necrosis in the three groups: 3.1±0.8 cm, 2.9±1.2 cm and 4.0±1.3 cm in groups A, B and C, respectively (p > 0.05). The temperature at 15 mm from the electrode was higher in group C than in the other groups: 70±18℃ in group A, 59±23℃ in group B and 96±16℃ in group C (p < 0.05).

Conclusion

Saline-enhanced bipolar RFA using dual perfused-cooled electrodes increases the dimension of the ablation zone more efficiently than monopolar RFA or single probe bipolar RFA.     

Percutaneous Radiofrequency Thermal Ablation with Hypertonic Saline Injection: In Vivo Study in a Rabbit Liver Model

Objective

To determine whether hypertonic saline (HS, 36% NaCl) injection prior to or during radiofrequency ablation (RFA) can increase the extent of thermally mediated coagulation in in-vivo rabbit liver tissue, and also to establish the ideal injection time in relation to RFA in order to maximize its effect on the extent of radiofrequency (RF)-induced coagulation.

Materials and Methods

In 26 rabbits, 43 RFA lesions were produced using a 17-gauge internally cooled electrode with a 1-cm active tip under ultrasound (US) guidance. Rabbits were assigned to one of three groups: Group A: RFA alone (n=8); Group B: RFA after the instillation of 1 mL HS (n=8); Group C: RFA after and during the instillation of 0.5 mL HS (n=10). RF energy (30 W) was applied for 3 minutes, and changes occurring in tissue impedance, current, power output, and the temperature of the electrode tip were automatically measured. After RFA, contrast-enhanced spiral CT was performed, and in each group the maximum diameters of the thermal lesions in gross specimens were compared. Technical success and the complications arising were evaluated by CT and on the basis of autopsy findings.

Results

All procedures were technically successful. There were six procedure-related complications (6/26; 23%), including five localized perihepatic hematomas and one thermal injury to the stomach. With instillation of HS in group B rabbits, markedly decreased tissue impedance (73Ω ± 5) and increased current (704 mA ± 41) were noted, compared to RF ablation without saline infusion (116.3Ω ± 13, 308 mA ± 80). With instillation of the solution before RFA (group B), coagulation necrosis was greater (14.9 mm ± 3.8) than in rabbits not injected (group A: 11.5 mm ± 2.4; Group A vs. B: p < .05) and in those injected before and during RFA (group C: 12.5 mm ± 3.1; Group B vs. C: p > .05).

Conclusion

RFA using HS instillation can increase the volume of RFA-induced necrosis of the liver with a single application, thereby simplifying and accelerating the treatment of larger lesions. In addition, HS instillation before RFA more effectively achieves coagulation necrosis than HS instillation before and during RFA.     

A Newly Developed Perfused Umbrella Electrode for Radiofrequency Ablation: An Ex Vivo Evaluation Study in Bovine Liver

The purpose of this study was to evaluate the effectiveness of a newly developed perfused monopolar radiofrequency (RF) probe with an umbrella-shaped array. A perfused umbrella-shaped monopolar RF probe based on a LeVeen electrode (Boston Scientific Corp., Natick, MA, USA) with a 3-cm array diameter was developed. Five different configurations of this electrode were tested: (a) perfusion channel/endhole, (b) perfusion channel/endhole + sideholes, (c) 1 cm insulation removed at the tip, (d) 1 cm insulation removed at the tip + perfusion channel/endhole, and (e) 1 cm insulation removed at the tip + perfusion channel/endhole + sideholes. An unmodified LeVeen electrode served as a reference standard. RF ablations were performed in freshly excised bovine liver using a commercial monopolar RF system with a 200-W generator (RF 3000; Boston Scientific Corp.). Each electrode was tested 10 times applying the vendor’s recommended ablation protocol combined with the preinjection of 2 ml 0.9% saline. Volumes and shapes of the lesions were compared. Lesions generated with the original LeVeen electrode showed a mean volume of 12.74 ± 0.52 cm3. Removing parts of the insulation led to larger coagulation volumes (22.65 ± 2.12 cm3). Depending on the configuration, saline preinjection resulted in a further increase in coagulation volume (25.22 ± 3.37 to 31.28 ± 2.32 cm³). Besides lesion volume, the shape of the ablation zone was influenced by the configuration of the electrode used. We conclude that saline preinjection in combination with increasing the active tip length of the umbrella-shaped LeVeen RF probe allows the reliable ablation of larger volumes in comparison to the originally configured electrode.     

Ex Vivo Experiment of Saline-Enhanced Hepatic Bipolar Radiofrequency Ablation with a Perfused Needle Electrode: Comparison with Conventional Monopolar and Simultaneous Monopolar Modes

The purpose of this study was to validate the saline-enhanced bipolar radiofrequency ablation (RFA) technique using a perfused electrode to increase RF-created coagulation necrosis, to compare that technique with monopolar RFAs and to find appropriate concentrations and volumes of perfused NaCl solution for the bipolar RFA. A total of 90 ablations were performed in explanted bovine livers. In the initial experiments to determine appropriate conditions for bipolar RFA, we created five thermal ablation zones in each condition, with instillations of varied concentrations (0.9–36%) or injection rates (30 mL/hr–120 mL/hr) of NaCl solution. After placement of one or two 16-gauge open-perfused electrodes into bovine livers, the NaCl solution was instilled into the tissue through the electrode. In the second part of the study, 10 ablation zones were created using one or two perfused electrodes for each of five groups under different conditions: a conventional monopolar mode with 0.9% NaCl solution (group A) or with 6% NaCl solution (group B), a simultaneous monopolar mode with 6% NaCl solution (group C) and a bipolar mode with 6% NaCl solution (groups D and E). RF was applied to each electrode for 20 min in groups A, B, C, and E, or for 10 min in group D. During RFA, we measured the tissue temperature 15 mm from the electrode. The temperature changes during the RFA and the dimensions of the ablation zones were compared among the groups. Bipolar RFA created larger short-axis diameters of coagulation necrosis with 6% NaCl solution (35.8 ± 15 mm) than with 0.9% NaCl solution (17 ± 9.7 mm) (P < 0.05). However, concentrations of NaCl solution above 6% did not further increase the extent of coagulation necrosis. In addition, bipolar RFA with 6% NaCl solution instillation at a rate of 1.0 mL/min (37.9 ± 5.4 mm) or 2.0 mL/min (35.6 ± 9.3 mm) produced larger diameters at the mid-point between the electrodes of the ablated lesion than did 0.5 mL/min (25.8 ± 9.3 mm) (P < 0.05). The bipolar mode showed a more rapid increase in temperature at the mid-point between the two probes, up to 60°C, than did the monopolar modes (P < 0.05). In addition, the bipolar RFA (group E) treated for 20 min showed a larger value of the short-axis diameter than did the conventional or simultaneous monopolar modes (P < 0.05), and bipolar RFA (group D) treated for 10 min, showed similar results with conventional monopolar modes treated for 20 min (P > 0.05): 31.0 ± 5.4 mm (group A); 28.8 ± 3.8 mm (group B); 25.5 ± 6.4 mm (group C); 32.6 ± 4.2 mm (group D); 49.4 ± 5.0 mm (group E). Bipolar RFA with instillation of 6% NaCl solution through an open perfusion system demonstrates better efficacy in creating a larger ablation zone than does conventional or simultaneous monopolar modes at the various times examined. Therefore, hypertonic saline-enhanced bipolar RFA seems to be a promising approach for treating larger liver tumors.     

A Comparative Experimental Study of the In-vitro Efficiency of Hypertonic Saline-Enhanced Hepatic Bipolar and Monopolar Radiofrequency Ablation

Objective

To compare the in-vitro efficiency of a hypertonic saline (HS)-enhanced bipolar radiofrequency (RF) system with monopolar RF applications by assessing the temperature profile and dimensions of RF-created coagulation necrosis in bovine liver.

Materials and Methods

A total of 27 ablations were performed in explanted bovine livers. After placement of two 16-gauge open-perfused electrodes at an interelectrode distance of 3 cm, 5% HS was instilled into tissue at a rate of 1 mL/min through the electrode. Seventeen thermal ablation zones were created in the monopolar mode (groups A, B), and ten more were created using the two open-perfused electrodes in the bipolar mode (group C). RF was applied to each electrode for 5 mins (for a total of 10 mins, group A) or 10 mins (for a total of 20 mins, group B) at 50W in the sequential monopolar mode, or to both electrodes for 10 min in the bipolar mode (group C). During RF instillation, we measured tissue temperature at the midpoint between the two electrodes. The dimensions of the thermal ablation zones and changes in impedance and wattage during RFA were compared between the groups.

Results

With open-perfusion electrodes, the mean accumulated energy output value was lower in the bipolar mode (group C: 26675 ± 3047 Watt·s) than in the monopolar mode (group A: 28778 ± 1300 Watt·s) but the difference was not statistically significant (p > 0.05). In the bipolar mode, there were impedance rises of more than 700 Ω during RF energy application, but in the monopolar modes, impedance did not changed markedly. In the bipolar mode, however, the temperature at the mid-point between the two probes was higher (85℃) than in the monopolar modes (65℃, 80℃ for group A, B, respectively) (p < 0.05). In addition, in HS-enhanced bipolar RFA (group C), the shortest diameter at the midpoint between the two electrodes was greater than in either of the monopolar modes: 5.4 ± 5.6 mm (group A); 28.8 ± 8.2 mm (group B); 31.2 ± 7.6 mm (group C) (p < 0.05)

Conclusion

Using an open perfusion system, HS-enhanced bipolar RFA more efficiently created larger areas of thermal ablation and higher tissue temperatures than monopolar RFA.     

Combined Radiofrequency Ablation and Acetic Acid Hypertonic Saline Solution Instillation: An In Vivo Study of Rabbit Liver

Objective

We wanted to determine whether combined radiofrequency ablation (RFA) and acetic acid-hypertonic saline solution (AHS) instillation can increase the extent of thermally mediated coagulation in in vivo rabbit liver tissue. We also wished to determine the optimal concentration of the solution in order to maximize its effect on extent of the RFA-induced coagulation.

Materials and Methods

Forty thermal ablation zones were produced in 40 rabbits by using a 17-gauge internally cooled electrode with a 1-cm active tip under ultrasound guidance. The rabbits were assigned to one of four groups: group A: RFA alone (n=10); group B: RFA with 50% AHS instillation (n=10); group C: RFA with 25% AHS instillation (n=10); group D: RFA with 15% AHS instillation (n=10). A range of acetic acid concentrations diluted in 36% NaCl to a total volume of 1 mL were instilled into the liver before RFA. The RF energy (30 W) was applied for three minutes. After RFA, in each group, the maximum diameters of the thermal ablation zones in the gross specimens were compared. Technical success and the complications that arose were evaluated by CT and on the basis of autopsy findings.

Results

All procedures are technically successful. There were six procedure-related complications (6/40; 15%): two localized perihepatic hematomas and four chemical peritonitis. The incidence of chemical peritonitis was highest for group B with the 50% AHS solution instillation (30%). With instillation of 15% AHS solution, a marked decrease of tissue impedance (24.5 ± 15.6 Ω) and an increase of current (250 mA) occurred as compared to RFA alone. With instillation of the solutions before RFA (group B, C and D), this produced a greater mean diameter of coagulation necrosis than the diameters for rabbits not instilled with the solution (group A) (p < 0.05). However, there was no significant difference between group B, C, and D.

Conclusion

Combined AHS instillation and RFA can increase the dimension of coagulation necrosis in the liver with a single application. A low concentration of AHS (15%) showed similar effects in increasing the extent of RF-induced coagulation, but there were less side effects as compared to the high concentration of AHS.     

Radiofrequency Ablation for Treating Liver Metastases from a Non-Colorectal Origin

Objective

We wanted to assess the safety and efficacy of performing radiofrequency ablation (RFA) in patients with non-colorectal liver metastases.

Materials and Methods

In this retrospective study, 25 patients with 40 hepatic metastases (M:F = 17:8; mean age, 57 years; tumor size, 0.5-5.0 cm) from a non-colorectal origin (stomach, biliary, breast, pancreas, kidney and skin) were treated with RFA. The RFA procedures were performed using either an internally cooled electrode or a clustered electrode under ultrasound or CT guidance. Contrast-enhanced CT scans were obtained immediately after RFA and follow-up CT scans were performed within three months after ablation and subsequently at least every six months. The intrahepatic disease-free interval was estimated and the overall survival from the time of the initial RFA was analyzed using the Kaplan-Meier method.

Results

No intraprocedural deaths occurred, but four major complications developed, including abscesses (n = 3) and pneumothorax (n = 1). Technical effectiveness was determined on the initial follow-up images. During the follow-up period (range, 5.9-68.6 months; median time, 18.8 months) for 37 tumors in 22 patients where technical effectiveness was achieved, 12 lesions (32%, 12 of 37) showed local tumor progression and new intrahepatic metastases occurred in 13 patients (59%, 13 of 22). The median intrahepatic disease-free interval was 10.1 months. The 1-year, 3-year and 5-year overall survival rates after RFA were 86%, 39% and 19%, respectively.

Conclusion

RFA showed intermediate therapeutic effectiveness for the treatment of non-colorectal origin liver metastases.     

Influence of NaCl Concentrations on Coagulation,Temperature, and Electrical Conductivity Using a Perfusion Radiofrequency Ablation System: An Ex Vivo Experimental Study

Purpose To determine, by means of an ex vivo study, the effect of different NaCl concentrations on the extent of coagulation obtained during radiofrequency (RF) ablation performed using a digitally controlled perfusion device. Method Twenty-eight RF ablations were performed with 40 W for 10 min using continuous NaCl infusion in fresh excised bovine liver. For perfusion, NaCl concentrations ranging from 0 (demineralized water) to 25% were used. Temperature, the amount of energy, and the dimensions of thermal-induced white coagulation were assessed for each ablation. These parameters were compared using the nonparametric Mann-Whitney test. Correlations were calculated according to the Spearman test. Results RF ablation performed with 0.9% to 25% concentrations of NaCl produced a mean volume of coagulation of 30.7 ± 3.8 cm³, with a mean short-axis diameter of 3.6 ± 0.2 cm. The mean amount of energy was 21,895 ± 1,674 W and the mean temperature was 85.4 ± 12.8°C. Volume of coagulation, short-axis diameter, and amount of energy did not differ significantly among NaCl concentrations (p > 0.5). A correlation was found between the NaCl concentration and the short-axis diameter of coagulation (r = 0.64) and between the NaCl concentration and the mean temperature (r = 0.67), but not between the NaCl concentration and volume of coagulation. Conclusion In an ex vivo model, continuous perfusion with high NaCl concentrations does not significantly improve the volume of thermal-induced coagulation. This may be because the use of a low-power generator cannot sufficiently exploit the potential advantage of better tissue conductivity provided by NaCl perfusion.     

Percutaneous Radiofrequency Ablation with Multiple Electrodes for Medium-Sized Hepatocellular Carcinomas

Objective

To prospectively evaluate the safety and short-term therapeutic efficacy of switching monopolar radiofrequency ablation (RFA) with multiple electrodes to treat medium-sized (3.1-5.0 cm), hepatocellular carcinomas (HCC).

Materials and Methods

In this prospective study, 30 patients with single medium-sized HCCs (mean, 3.5 cm; range, 3.1-4.4 cm) were enrolled. The patients were treated under ultrasonographic guidance by percutaneous switching monopolar RFA with a multichannel RF generator and two or three internally cooled electrodes. Contrast-enhanced CT scans were obtained immediately after RFA, and the diameters and volume of the ablation zones were then measured. Follow-up CT scans were performed at the first month after ablation and every three months thereafter. Technical effectiveness, local progression and remote recurrence of HCCs were determined.

Results

There were no major immediate or periprocedural complications. However, there was one bile duct stricture during the follow-up period. Technical effectiveness was achieved in 29 of 30 patients (97%). The total ablation time of the procedures was 25.4 ± 8.9 minutes. The mean ablation volume was 73.8 ± 56.4 cm³ and the minimum diameter was 4.1 ± 7.3 cm. During the follow-up period (mean, 12.5 months), local tumor progression occurred in three of 29 patients (10%) with technical effectiveness, while new HCCs were detected in six of 29 patients (21%).

Conclusion

Switching monopolar RFA with multiple electrodes in order to achieve a sufficient ablation volume is safe and efficient. This method also showed relatively successful therapeutic effectiveness on short-term follow up for the treatment of medium-sized HCCs.     

Radiofrequency Ablation of the Gastrointestinal Tract with a Stent-Like Electrode: Experimental Study

Objective

To assess the technical feasibility of a newly designed stent-like electrode in rabbits.

Materials and Methods

A stent-like electrode was knitted from a single thread of nitinol wire and interconnected to a generator using similar wire. In order to gauge the extent of radiofrequency ablation (RFA), we measured the depth of the ablated area in cow liver using a combination of 180-sec time intervals and 20-watt power increments. For data processing, Cox regression analysis was used. RFA was also applied to the small intestine of rabbits using this stent-like electrode under six different sets of conditions: 10 watts for 1 min, 10 watts for 2 mins, 20 watts for 1 min, 20 watts for 2 mins, 30 watts for 1 min, and 30 watts for 2 mins. To determine the gross and microscopic findings, six animals were sacrificed immediately after the procedure and the results obtained under the different sets of conditions were correlated. Eight rabbits were monitored for 4 weeks prior to sacrifice.

Results

For both ex-vivo and in-vivo ablations, the depth of the thermal lesion showed linear correlation with both the duration of RFA and the power applied. RFA of the duodenum was technically successful in all 14 rabbits. The acute changes occurring in the rabbits'' small intestine included color change, cytoplasmic denaturation, fibrin deposition and hemorrhage, among which hemorrhage of the mucosal layer was the earliest finding. RF ablation for 2 mins at 30 watts caused serosal hemorrhage. The gross and histologic changes occurring showed close correlation under all six sets of conditions.

Conclusion

Use of the stent-like electrode proves technically feasible but to determine the nature of the chronic change occurring in the gastrointestinal tract after RF ablation, further investigation and long-term follow-up in animals are required.     

射频组织间热疗的实验研究

目的研究中空冷却射频仪在犬活体肝脏上的安全性及毁损情况.材料和方法16只犬分4组经历3,6,12,18min的射频毁损,观察毁损即时不同时间及3个月,6个月后毁损灶的大体、病理及温度改变.结果3,6,12,18min热疗即时分别产生1.0±0.1,2.2±0.1,3.0±0.15,3.0±0.lcm的毁损灶,无针尖周围结碳现象.3及6个月后毁损灶略缩小,内部逐渐液化,外由纤维组织包裹.结论中空冷却射频仪可产生较大毁损灶,并在12min内逐渐增大.     

Overlapping Ablation Using a Coaxial Radiofrequency Electrode and Multiple Cannulae System: Experimental Study in ex-Vivo Bovine Liver

Objective

To assess the sizes and configurations of thermal zones after overlapping ablations using a coaxial radiofrequency (RF) electrode and multiple cannulae in ex-vivo bovine liver.

Materials and Methods

For ablation procedures, a coaxial RF electrode and introducer set was used. Employing real-time ultrasound guidance and overlapping techniques in explanted, fresh bovine liver, we created five kinds of thermal zones with one (n=10), two (n=8), four (n=3), and six ablation spheres (n=3). Following ablation, MR images were obtained and the dimensions of all thermal zones were measured on the longitudinal or transverse section of specimens. The shape of the composite ablation zones was evaluated using three-dimensional MR image reconstruction.

Results

At gross pathologic examination of ten single-ablation zones (spheres), the long-axis (transverse) and short-axis lengths of zones ranged from 3.7 to 4.4 (mean, 4.1) cm and from 3.5 to 4.0 (mean, 3.7) cm, respectively. The long-axis (transverse) and short-axis lengths of double-ablation zones (cylinders) with 23% overlap ranged from 7.0 to 7.7 (mean, 7.3) cm and from 3.0 to 3.9 (mean, 3.5) cm, respectively; those with 58% overlap ranged from 6.0 to 6.4 (mean, 6.2) cm and from 3.8 to 4.6 (mean, 4.3) cm, respectively. The long-axis (diagonal) and short-axis lengths on a transverse section of four-ablation zones (cakes) ranged from 8.5 to 9.7 (mean, 9.1) cm and from 3.0 to 4.1 (mean, 3.7) cm, respectively. Gross pathologic examination of three composite six-ablation zones (spheres) showed that the long-axis (diagonal) and short-axis lengths of zones ranged from 9.0 to 9.9 (mean, 9.4) cm and from 6.8 to 7.5 (mean, 7.2) cm, respectively. T2-weighted MR images depicted low-signal thermal zones containing multiple curvilinear and spotty regions of hyperintensity.

Conclusion

Using a coaxial RF electrode and multiple cannulae, together with ultrasound guidance and precise overlapping ablation techniques, we successfully created predictable thermal zones in ex-vivo bovine liver.     

Combined Therapy of Radiofrequency Ablation and Ethanol Injection of Rabbit Liver: An <Emphasis Type="Italic">In Vivo</Emphasis> Feasibility Study

Our purpose was to compare the effects of percutaneous radiofrequency ablation (RFA) combined with percutaneous ethanol injection (PEI) on the extent of ablation in in vivo rabbit liver tissue as compared with either therapy alone. Twenty-two New Zealand white rabbits were included in this study and allocated into three groups: group A: conventional RFA (n = 6); group B: PEI (n = 6); group C: combined RFA and PEI (n = 10). For combined RFA and PEI, under ultrasound guidance, 1 mL of absolute ethanol was injected into the target area of the liver parenchyma through a 21-gauge Chiba needle before performing RFA. RFA was performed using a 17- gauge internally cooled electrode with 1-cm active tip, and RF energy (30 W) was applied for 3 minutes, with or without ethanol injection. After RFA or PEI, contrast-enhanced computed tomography and CT-pathologic correlation were performed. The short- axis and long-axis diameters of thermal lesions of each group were compared. All procedures were technically successful and a total of 38 lesions were produced. The mean short-axis and long-axis diameter of the coagulation necrosis in rabbits of group C (combination of RFA and PEI), were significantly larger than those of other groups: group A: 10.3 ± 2 mm and 11.4 ± 2 mm; group B: 3.1 ± 1 mm and 4.3 ± 2 mm; group C: 12.8 ± 3 mm and 17.8 ± 6 mm (p < 0.05). On contrast-enhanced CT scan, the lesions of rabbits of the group C appeared to be more frequently irregular compared to those of group A (20% in group A vs. 67% in group C). There were three complications including two localized hematomas and one cardiopulmonary failure. Combined RFA and PEI could increase the dimension of coagulation necrosis without increasing complications and therefore, may be successfully used for treating larger lesions.     

Ablative Outcomes of Various Energy Modes for No-Touch and Peripheral Tumor-Puncturing Radiofrequency Ablation: An Ex Vivo Simulation Study

ObjectiveTo compare the outcomes of radiofrequency ablation (RFA) using dual switching monopolar (DSM), switching bipolar (SB), and combined DSM + SB modes at two different interelectrode distances (25 and 20 mm) in an ex vivo study, which simulated ablation of a 2.5-cm virtual hepatic tumor.Materials and MethodsA total of 132 ablation zones were created (22 ablation zones for each protocol) using three separable clustered electrodes. The performances of the DSM, SB, and combined DSM + SB ablation modes were compared by evaluating the following parameters of the RFA zones at two interelectrode distances: shape (circularity), size (diameter and volume), peritumoral ablative margins, and percentages of the white zone at the midpoint of the two electrodes (ablative margin at midpoint, AMm) and in the electrode path (ablative margin at electrode path, AMe).ResultsAt both distances, circularity was the highest in the SB mode, followed by the DSM + SB mode, and was the lowest in the DSM mode. The circularity of the ablation zone showed a significant difference among the three energy groups (p < 0.001 and p = 0.002 for 25-mm and 20-mm, respectively). All size measurements, AMm, and AMe were the greatest in the DSM mode, followed by the DSM + SB mode, and the lowest were with the SB mode (all statistically significant). The white zone proportion in AMm and AMe were the greatest in the SB mode, followed by the DSM + SB mode and DSM in general.ConclusionDSM and SB appear to be complementary in creating an ideal ablation zone. RFA with the SB mode can efficiently eradicate tumors and create a circular ablation zone, while DSM is required to create a sufficient ablative margin and a large ablation zone.     

Radiofrequency ablation in the liver using two cooled-wet electrodes in the bipolar mode

The purpose of this study was to demonstrate the efficacy of bipolar radiofrequency ablation (RFA) using cooled-wet electrodes inducing coagulation in ex vivo bovine livers and in in vivo canine livers. In ex vivo experiments, 20 coagulations were created by monopolar (group A), and bipolar RFA (group B) using a 200 W generator (Valleylab) and one or two cooled-wet electrodes. In in vivo experiments, one coagulation was created by bipolar RFA in each of eight dogs via laparotomy. In ex vivo and in vivo experiments, RF was applied to one or two electrodes at 100 W for 10 min. The dimensions of the coagulations were compared in the two groups. In ex vivo experiments, the mean volumes of the coagulations produced in group B (54.0±16.5 cm³) were greater than those produced in group A (33.9±12.7 cm³) (P=0.007). In in vivo experiments, bipolar RFA produced a coagulation of 39.4±15.6 cm³ without a major complication. The present study showed that a RF electrode system using two cooled-wet electrodes in the bipolar mode created larger coagulation volumes than the monopolar mode, and this system can be used to create large coagulation without major complications.An erratum to this article can be found at     

Bipolar radiofrequency ablation in ex vivo bovine liver with the open-perfused system versus the cooled-wet system

The aim of this study was to investigate the efficacy of bipolar radiofrequency ablation (RFA) with the open-perfused electrode and cooled-wet electrode. Bipolar RF was applied for 20 min to the ex vivo bovine liver using either the Berchtold system with two 16-gauge open-perfused electrodes (group A, n=15) or the Radionics system with two 15-gauge cooled-wet electrodes (group B, n=15). In both groups, two electrodes were placed 3 cm apart. The ablation zone was created by the RF energy delivered together with the infusion of 5% hypertonic saline (2 ml/min). The dimension of the ablation zone, its shape and the changes in the impedance and W s of two groups during the RFA were examined and documented. The vertical diameter (Dv) along the probe, the long-axis diameter (Dl) perpendicular to the Dv in the longitudinal plane and the short-axis diameter of the ablation zone (Ds) in the transverse plane through the midpoint between the tips of two probes were measured. The mean accumulated energy output in the Radionics system was higher than in the Berchtold system (159,887.0±36,423 W s vs. 87,555.1±86,787 W s). The difference was statistically significant (P<0.05). In group A, the impedance intermittently rose to above 700 during the RFA in all sessions, which led to a gradual decrease of the power output to lower than 30 W. In group B, on the other hand, the impedance did not change markedly. The mean Dv value of the coagulation necrosis in group B was significantly longer than in group A (5.0±0.4 cm vs. 4.3±0.6 cm, P<0.05). The mean Dl and Ds were 6.7±0.5 cm and 5.0±0.8 cm in group A, and 6.5±0.8 cm and 5.5±0.7 cm in group B, respectively (P>0.05). The data demonstrate that the cooled-wet electrode generates the more spherical ablation zone than the open-perfused electrode. With approximately doubled power output, the bipolar RFA with the cooled-wet electrodes induces a larger volume of tissue coagulation than with the open-perfused electrodes.     

Radiofrequency Thermal Ablation: Increase in Lesion Diameter with Continuous Acetic Acid Infusion

Purpose To evaluate the influence of continuous infusion of acetic acid 50% during radiofrequency ablation (RFA) on the size of the thermal lesion produced. Methods Radiofrequency (RF) was applied to excised bovine liver by using an expandable needle electrode with 10 retractable tines (LeVeen Needle Electrode, RadioTherapeutics, Sunnyvale, CA) connected to a commercially available RF generator (RF 2000, RadioTherapeutics, Sunnyvale, CA). Experiments were performed using three different treatment modalities: RF only (n = 15), RF with continuous saline 0.9% infusion (n = 15), and RF with continuous acetic acid 50% infusion (n = 15). RF duration, power output, tissue impedance, and time to a rapid rise in impedance were recorded. The ablated lesions were evaluated both macroscopically and histologically. Results The ablated lesions appeared as spherical or ellipsoid, well-demarcated pale areas with a surrounding brown rim with both RF only and RF plus saline 0.9% infusion. In contrast, thermolesions generated with RF in combination with acetic acid 50% infusion were irregular in shape and the central portion was jelly-like. Mean diameter of the coagulation necrosis was 22.3 ± 2.1 mm (RF only), 29.2 ± 4.8 mm (RF + saline 0.9%) and 30.7 ± 5.7 mm (RF + acetic acid 50%), with a significant increase in the RF plus saline 0.9% and RF plus acetic acid 50% groups compared with RF alone. Time to a rapid rise in impedance was significantly prolonged in the RF plus saline 0.9% and RF plus acetic acid 50% groups compared with RF alone. Conclusions A combination of RF plus acetic acid 50% infusion is able to generate larger thermolesions than RF only or RF combined with saline 0.9% infusion.