Dual Switching Monopolar Radiofrequency Ablation Using a Separable Clustered Electrode: Comparison with Consecutive and Switching Monopolar Modes in Ex Vivo Bovine Livers

OBJECTIVE: To compare the in-vitro efficiency of dual-switching monopolar (DSM) radiofrequency ablation (RFA) using a separable clustered electrode (Octopus(R) electrodes) with consecutive monopolar (CM) and switching monopolar (SM) RFA techniques to create an ablative zone in the explanted bovine liver. MATERIALS AND METHODS: For DSM-RFA, we used a prototype, three-channel, dual generator RFA Unit and Octopus(R) electrodes with three, 17 gauge internally cooled electrodes. The RFA Unit allowed simultaneous radiofrequency (RF) energy delivery to two electrodes of the Octopus(R) electrodes as well as automatic switching among the three electrode pairs according to the impedance changes. RF energy was sequentially applied to one of the three electrodes for 24 minutes (group A; CM mode, n = 10) or alternatively applied for 12 minutes (group B; SM mode, n = 10) or concurrently applied to a pair of electrodes for 12 minutes (group C; DSM mode, n = 10) in explanted bovine livers. Changes in the impedance and current during RFA as well as the dimensions of the thermal ablative zones were compared among the three groups. RESULTS: The mean, delivered RF energy amounts in groups A, B, and C were 63.15 +/- 8.6 kJ, 72.13 +/- 5.4 kJ, and 106.08 +/- 13.4 kJ, respectively (p < 0.001). The DSM mode created a significantly larger ablation volume than did the other modes, i.e., 68.1 +/- 10.2 cm3 (group A), 92.0 +/- 19.9 cm3 (group B), and 115.1 +/- 14.0 cm3 (group C) (p < 0.001). The circularity in groups A, B, and C were 0.84 +/- 0.06, 0.87 +/- 0.04 and 0.90 +/- 0.03, respectively (p = 0.03). CONCLUSION: DSM-RFA using Octopus(R) electrodes can help create large ablative zones within a relatively short time.

Radiofrequency Ablation with Epinephrine Injection: In Vivo Study in Normal Pig Livers

PURPOSE: We wanted to evaluate whether epinephrine injection prior to radiofrequency (RF) ablation can increase the extent of thermally mediated coagulation in vivo normal pig liver tissue. MATERIALS AND METHODS: Eighteen RF ablation zones were created in six pigs using a 17-gauge internally cooled electrode under ultrasound guidance. Three RF ablation zones were created in each pig under three conditions: RF ablation alone, RF ablation after the injection of 3 mL of normal saline, and RF ablation after the injection of 3 mL of epinephrine (1:10,000 solution). After the RF ablation, we measured the short and long diameters of the white zones in the gross specimens. RESULTS: Three of the RF ablations were technically unsuccessful; therefore, measurement of white zone was finally done in 15 RF ablation zones. The mean short and long diameters of the white zone of the RF ablation after epinephrine injection (17.2 mm +/- 1.8 and 20.8 mm +/- 3.7, respectively) were larger than those of RF ablation only (10 mm +/- 1.2 and 12.2 mm +/- 1.1, respectively) and RF ablation after normal saline injection (12.8 mm +/- 1.5 and 15.6 mm +/- 2.5, respectively) (p < .05). CONCLUSION: RF ablation with epinephrine injection can increase the diameter of the RF ablation zone in normal pig liver tissue.

Hepatic Radiofrequency Ablation Using Multiple Probes: Ex Vivo and In Vivo Comparative Studies of Monopolar versus Multipolar Modes

OBJECTIVE: We wanted to compare the efficiency of multipolar radiofrequency ablation (RFA) using three perfused-cooled electrodes with multiple overlapping- and simultaneous monopolar techniques for creating an ablation zone in ex vivo bovine livers and in in vivo porcine livers. MATERIALS AND METHODS: In the ex vivo experiments, we used a 200 W generator (Valleylab, CC-3 model) and three perfused-cooled electrodes or internally cooled electrodes to create 30 coagulation zones by performing consecutive monopolar RFA (group A, n = 10), simultaneous monopolar RFA (group B, n = 10) or multipolar RFA (group C, n = 10) in explanted bovine livers. In the consecutive mode, three ablation spheres were created by sequentially applying 150 watts radiofrequency (RF) energy to the internally cooled electrodes for 12 minutes each for a total of 36 minutes. In the simultaneous monopolar and multipolar modes, RF energy was concurrently applied to the three perfused-cooled electrodes for 20 minutes at 150 watt with instillation of 6% hypertonic saline at 2 mL/min. During RFA, we measured the temperatures of the treated area at its center. The changes in impedance, the current and liver temperature during RFA, as well as the dimensions of the thermal ablation zones, were compared among the three groups. In the in vivo experiments, three coagulations were created by performing multipolar RFA in a pig via laparotomy with using same parameter as the ex vivo study. RESULTS: In the ex vivo experiments, the impedance was gradually decreased during the RFA in groups B and C, but in group A, the impedance was increased during RFA and this induced activation by the pulsed RF technique. In groups A, B and C, the mean final-temperature values were 80 +/- 10 degrees C, 69+/-18 degrees C and 79 +/- 12 degrees C, respectively (p < 0.05). The multipolar mode created a larger volume of ablation than did the other modes: 37.6 +/-4.0 cm3 (group A); 44.9 +/- 12.7 cm3 (group B); and 78.9 +/- 6.9 cm3 (group C) (p < 0.05). In the in vivo experiment, the pig well tolerated the RFA procedure and no major complications occurred during the 4 days of the follow-up period. The mean volume of coagulations produced by multipolar RFA in the pig liver was 60.5+/-17.9 cm3. CONCLUSION: For the multiple probe RFA, the multipolar mode with hypertonic saline instillation was more efficient in generating larger areas of thermal ablation than either the consecutive or simultaneous monopolar modes.

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 15 mm 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 temperature at 15 mm from the electrode was higher in group C than in the other groups: 70+/-18 degrees C in group A, 59+/-23 degrees C in group B and 96+/-16 degrees C 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.

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. MAERIALS 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 omega) 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.

An Experimental Study of Simultaneous Ablation with Dual Probes in Radiofrequency Thermal Ablation

PURPOSE: To determine the differences between sequential ablation with a single probe and simultaneous ablation with dual probes. MATERIALS AND METHODS : Using two 14-gauge expandable probes (nine internal prongs with 4-cm deployment), radiofrequency was applied sequentially (n=8) or simultaneously (n=8) to ten ex-vivo cow livers. Before starting ablation, two RF probes with an inter-probe space of 2 cm (n=8) or 3 cm (n=8) were inserted. In the sequential group, switching the connecting cable to an RF generator permitted ablation with the second probe just after ablation with the first probe had finished. In the simultaneous group, single ablation was performed only after connecting the shafts of both RF probes using a connection device. Each ablation lasted 7 minutes at a target temperature of 105-110 degrees C. The size and shape of the ablated area, and total ablation time were then compared between the two groups. RESULTS: With 2-cm spacing, the group, mean length and overlapping width of ablated lesions were, respectively, 5.20 and 5.05 cm in the sequential group (n=4), and 5.81 and 5.65 cm in the simultaneous group (n=4). With 3-cm spacing, the corresponding figures were 4.99 and 5.60 cm in the sequential group (n=4), and 6.04 and 6.78 cm in the simultaneous group (n=4). With 2-cm spacing, the mean depth of the proximal waist was 0.58 cm in the sequential (group and 0.28 cm in the simultaneous group, while with 3-cm spacing, the corresponding figures were 1.65 and 1.48 cm. In neither group was there a distal waist. Mean total ablation time was 23.4 minutes in the sequential group and 14 minutes in the simultaneous group. CONCLUSION: In terms of ablation size and ablation time, simultaneous radiofrequency ablation with dual probes is superior to sequential ablation with a single probe. A simultaneous approach will enable an operator to overcome difficulty in probe repositioning during overlapping ablations, resulting in complete ablation with a successful safety margin.

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 (73 omega+/-5) and increased current (704 mA+/-41) were noted, compared to RF ablation without saline infusion (116.3 omega+/-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). CONCLUSION: RFA using HS instillation can increase the volume of RFAinduced 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 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 omega 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 (85degrees C) than in the monopolar modes (65degrees C, 80degrees C 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.

The Feasibility of CT-Guided Percutaneous Ethanol Injection Therapy for Hepatic Tumors

PURPOSE: To describe the technical features of CT-guided percutaneous ethanol injection therapy (PEIT) for hepatic tumors that are undetectable or inaccessible under ultrasound guidance, to analyze its short-term therapeutic results, and to discuss its feasibility and limitations with a review of the related literature. MATERIALS AND METHODS: During a 22-month period, 17 patients with 28 hepatic tumors (27 hepatocellular carcinomas and one metastasis) underwent 38 sessions of CT-guided PEIT. Follow-up CT scanning was also performed. All tumors were undetectable or inaccessible under ultrasound guidance. The quantity of ethanol injected depended on their maximum diameter, which was 0.9 -5.1 (mean, 2.2) cm. To determine the puncture site and direction of the needle, the graduated grid system was used. A 21 or 22-G PEIT needle was introduced into the tumor stepwise, with intermittent CT monitoring, and if the CT images obtained immediately after initial injection demonstrated incomplete perfusion, an additional dose of ethanol was administered. During the follow-up period of 28 -619 (mean, 261) days, three-phase spiral CT scans were obtained. We focused on whether or not a viable portion of ablated tumor was present, and if so, the interval during which the extent of viable portion had changed, as well as the CT findings which suggested a predisposition to incomplete ablation. RESULTS: PEIT was successfully performed in all patients. During each session, 3 -30 (mean, 12.1) mL of ethanol was injected for 35 -115 (mean, 85) mins, with 1 -7 (mean, 3.7) trials to determine the puncture site and needle direction. The follow-up CT results showed that 20 tumors (71.4%) contained no viable portion, that this portion had decreased in four (14.3%), and was unchanged or had increased in four (14.3%). In the eight tumors for which multiple sessions were required, follow-up CT showed that the viable portion was absent or had decreased in size in all except one. In five of the patients with a tumor containing a viable portion at follow- up CT, the procedure was incomplete because of unendurable pain (n = 2) or noncooperation (n = 3). A CT finding which suggested a predisposition to incomplete ablation was a poor margin (n = 3). Complications included severe pain (n = 6) and scanty peritoneal hemorrhage (n = 1). CONCLUSION: Despite several limitations of our study, the therapeutic results of CT-guided PEIT appeared to be similar to or slightly worse than those of well-established ultrasound-guided PEIT with the former procedure, however, intermittent CT monitoring indicates whether perfusion is complete, and for this reason, CT-guided PEIT is believed to be an effective treatment modality when a hepatic tumor is undetectable or inaccessible under ultrasound guidance.

Efficacy of Percutaneous Microwave Coagulation Therapy for Nodular Hepatic Tumor: A Preliminary Study

PURPOSE: Percutaneous microwave coagulation therapy (PMCT) uses a new energy source, microwave, in the treatment of solid neoplasms. We evaluated the efficacy of PMCT for nodular hepatic tumors in nine patients. MATERIALS AND METHODS: Between December 1998 and June 1999, we performed PMCT in six patients with hepatocellular carcinoma (HCC), two with one and three metastatic nodules each from colon cancer, and one with adenomatous hyperplasia. Four patients were female and five were male, and their age ranged between 44 and 71 (mean, 58.8) years. Under sonographic guidance a 14-gauge guiding needle was inserted percutaneously toward the lesion, and within it a needle electrode was precisely positioned. Microwave 2450MHz in frequency and with 60 or 80 watt emission was generated for 80~90 seconds. We evaluated the ultrasound findings obtained during the procedure, pre-PMCT and follow-up CT images, changes in tumor marker(AFP or CA19-9) levels and the results of liver function tests, and complications arising during the six-month period following PMCT. RESULTS: Immediately after microwave emission, characteristic hyperechogenicity appeared on the realtime sonogram. Two patients with HCC underwent CT before PMCT, and typical enhancement during the arterial phase and washout during the portovenous phase was observed. In one patient, two metastatic lesions from colon cancer showed delayed enhancement on pre-PMCT CT. Initial follow-up CT, performed between 1 and 4 weeks after the PMCT procedure, showed that eight lesions-including two HCCs which were highly enhanced on CT before PMCT-showed no contrast enhancement, and three others showed delayed enhancement. Two of the eight lesions which showed no contrast enhancement at initial follow-up CT were markedly decreased in size (from 2.9 and 4.0 cm to 1.0 and 2.0 cm, respectively) at subseqent follow-up 3 months and 6 months later, respectively. One of the three lesions showing delayed enhancement had increased in size from 4.1 to 5.5 cm at subsequent follow-up CT, 2 months later. Serum AFP or CA19-9 levels decreased in four of six patients (66.7%) who were followed up for 6 months. Transient elevation of aspartate aminotransferase(AST) levels were noted in all patients. PMCT-related complications included intrahepatic arterioportal shunt in two patients, pleural effusion in one, skin burn in one, intraperitoneal hemorrhage in one, and mild fever, abdominal pain and nausea in seven. No complications were serious, however. CONCLUSION: Our preliminary experiences suggest that PMCT is a safe and effective treatment modality for nodular hepatic tumors.

Percutaneous Microwave Coagulation Therapy combined with Transcatheter Arterial Chemoembolization for Hepatocellular Carcinoma: Preliminary Results

PURPOSE: To evaluate the efficacy of percutaneous microwave coagulation therapy (PMCT) combined with transcatheter arterial chemoembolization (TACE) for the treatment of hepatocellular carcinoma (HCC). MATERIALS AND METHODS: Twenty-five nodular HCCs [long diameter of 1.2 -10 (mean, 3.4) cm] in 19 patients (15males and 4 females) were treated by PMCT 4-138 days after TACE. Under ultrasound guidance, the carcinomas were punctured with a 14-G guideneedle through which a microwave electrode(25.0 cm in length, 1.6mm in diameter) was inserted. To coagulate the HCCs and surrounding hepatic parenchyma, microwave irradiation at 60W for 45 -60 seconds was then applied. One to three sessions of PMCT were performed at intervals of 2-6 days, and one week to 29 months later, the therapeutic effect was evaluated by spiral CT, angiography, and serum alpha-fetoprotein. RESULTS: Eighteen of 25 HCCs (72.0%) were necrotized completely, but seven (28.0%) recurred. Ninety percent of HCCs smaller than 4 cm in long diameter showed complete remission, but all those larger than 4 cm recurred. Alpha-fetoprotein levels decreased markedly in five patients (26.3%), while in 12 (63.2%), asparate aminotransferase (AST)/alanine aminotransferase (ALT) showed transient elevation. Minor complications occurred after PMCT (mild abdominal pain in 8 patients, fever in 7, pleural effusion in 3, portal vein thrombosis in 1, and hepatic abscess in 1), but in no case was this serious. CONCLUSION: PMCT combined with TACE provides effective and safe treatement for nodular HCCs with a long diameter of less than 4 cm.

Microwave Tissue Coagulation: Effects of Power and Treatment Time on Coagulation size

PURPOSE: To determine the effects of power and coagulation time on lesion size of ex-vivo bovine liver using microwaves. MATERIALS AND METHODS: Six bovine livers were divided into two groups(first group: 30W output, secondgroup: 60W output) and microwave coagulation was performed for 30, 60, and 120 sec. thermal injury site was thenobserved by means of sonography, and the maximal transverse diameter of the echo-change portion after microwave coagulation was measured. On the section of specimen, maximal transverse diameters of the thermal injury site weremeasured by gross inspection and compared with the result of sonographic measurement. RESULTS: Maximal transversediameters of hyperechoic lesions of the first group, as seen on sonography were 8.3 mm, 12.2mm, and 15.6mm, andthe maximal transverse diameters of thermal injury sites on gross specimens were 9.1mm, 12.0mm, and 15.1mm,respectively. Maximal transverse diameters of hyperechoic lesions of the second group, as seen on sonography, were12.1 mm, 17.4 mm, and 21.2 mm and maximal transverse diameters of thermal injury sites on gross specimens were13.2 mm, 16.0 mm, and 20.0 mm, respectively. Statistically maximal transverse diameters of hyperechoic lesions, asseen on sonography, correlated closely with the gross findings of maximal transverse diameters of thermal injurysites(p<0.05). CONCLUSION: Maximal transverse diameters of thermal injury sites were significantly increased asthe output of the microwave coagulator and the duration of coagulation time increased(p<0.05).