Assessment of Therapeutic Response of Ablated Lesion after Radiofrequency Ablation in Patients with Unresectable Lung Malignancies by Multiphase Contrast-enhanced MRI

PURPOSE: We evaluated which phase was important to recognize local progression of an ablated zone after RFA on multiphase contrast-enhanced MRI (CE-MRI) in patients with unresectable lung malignancy. MATERIALS AND METHODS: Twenty patients who had unresectable lung malignancy underwent multiphase CE-MRI examinations immediately after RFA. We evaluated the enhancement patterns of the ablated zone on multiphase CE-MRI: type I, no enhancement of the ablated zone; type II, enhancement of the ablated margin; type III, heterogeneous enhancement of the ablated zone. We evaluated the association enhancement type with local progression of the ablated zone on the follow up CT using Spearman's ranked test. RESULTS: In complete ablation, the enhancement pattern was types I (11.1%) or II (88.9%). In unsuccessfully treated, type II (57.1%) or III (42.9%) pattern observed in the arterial phase. However, types II (21.4%) and III (78.6%) observed in the venous, and types II (7.1%) and III (92.9%) observed equilibrium phases. Local progression of the ablated zone was associated with the enhancement pattern in equilibrium phases (r=0.8, p < .05). CONCLUSION: Equilibrium phases on multiphase CE-MRI might play a more important role in evaluating an ablated zone for predicting local recurrence after RFA.

Does Artificial Ascites Induce the Heat-Sink Phenomenon during Percutaneous Radiofrequency Ablation of the Hepatic Subcapsular Area?: an in vivo Experimental Study Using a Rabbit Model

OBJECTIVE: To evaluate the effect of the heat-sink phenomenon induced by artificial ascites on the size of the ablation zone during percutaneous radiofrequency (RF) ablation of the hepatic subcapsular area in an in vivo rabbit model. MATERIALS AND METHODS: A total of 21 percutaneous rabbit liver RF ablations were performed with and without artificial ascites (5% dextrose aqueous solution). The rabbits were divided into three groups: a) control group (C, n = 7); b) room temperature ascites group (R, n = 7); and c) warmed ascites group (W, n = 7). The tip of a 1 cm, internally cooled electrode was placed on the subcapsular region of the hepatic dome via ultrasound guidance, and ablation was continued for 6 min. Changes in temperature of the ascites were monitored during the ablation. The size of the ablation zones of the excised livers and immediate complications rates were compared statistically between the groups (Mann-Whitney U test, Kruskal-Wallis test, linear-by-linear association, p = 0.05). RESULTS: One rabbit from the "W" group expired during the procedure. In all groups, the ascites temperatures approached their respective body temperatures as the ablations continued; however, a significant difference in ascites temperature was found between groups "W" and "R" throughout the procedures (39.2 +/- 0.4 degrees C in group W and 33.4 +/- 4.3 degrees C in group R at 6 min, p = 0.003). No significant difference was found between the size of the ablation zones (782.4 +/- 237.3 mL in group C, 1,172.0 +/- 468.9 mL in group R, and 1,030.6 +/- 665.1 mL in group W, p = 0.170) for the excised liver specimens. Diaphragmatic injury was identified in three of seven cases (42.9%) upon visual inspection of group "C" rabbits (p = 0.030). CONCLUSION: Artificial ascites are not likely to cause a significant heat-sink phenomenon in the percutaneous RF ablation of the hepatic subcapsular region.

Percutaneous Radiofrequency Ablation of Hepatocellular Carcinomas Adjacent to the Gallbladder with Internally Cooled Electrodes: Assessment of Safety and Therapeutic Efficacy

OBJECTIVE: The objective of this study was to evaluate the safety and therapeutic efficacy of percutaneous radiofrequency (RF) ablation for the treatment of hepatocellular carcinomas (HCCs) adjacent to the gallbladder with the use of internally cooled electrodes. MATERIALS AND METHODS:We retrospectively assessed 45 patients with 46 HCCs (mean size, 2.2 cm) adjacent to the gallbladder ( or =3 cm) and tumor location (a tumor that abutted the gallbladder) were associated with an increased risk of early incomplete treatment. No variable was significantly associated with local tumor progression. CONCLUSION: Percutaneous RF ablation of HCCs adjacent to the gallbladder using an internally cooled electrode is a safe and effective treatment. Significant risk factors that lead to early incomplete treatment include tumor size, tumor location and electrode direction.

Radiofrequency Ablation Using a Monopolar Wet Electrode for the Treatment of Inoperable Non-Small Cell Lung Cancer: a Preliminary Report

OBJECTIVE: To assess the technical feasibility and complications of radiofrequency ablation (RFA) using a monopolar wet electrode for the treatment of inoperable non-small cell lung malignancies. MATERIALS AND METHODS: Sixteen patients with a non-small cell lung malignancy underwent RFA under CT guidance. All the patients were non-surgical candidates, with mean maximum tumor diameters ranging from 3 to 6 cm (mean: 4.6 +/- 1.1 cm). A single 16-gauge open-perfused electrode with a 2 cm exposed tip was used for the procedure. A 0.9% NaCl saline solution was used as the perfusion liquid with the flow adjusted to 30 mL/h. The radiofrequency energy was applied for 10-40 minutes. The response to RFA was evaluated by performing contrast-enhanced CT immediately after RFA, one month after treatment and then every three months thereafter. RESULTS: Technical failure was observed in six (37.5%) of 16 patients: intractable pain (n = 2) and non-stop coughing (n = 4). The mean follow-up interval was 15 +/- 8 months (range: 9-31 months). The mean maximum ablated diameter in the technically successful group of patients ranged from 3.5 to 7.5 cm (mean 5.1 +/- 1.3 cm). Complete necrosis was attained for eight (80%) of 10 lesions, and partial necrosis was achieved for two lesions. There were two major complications (2/10, 20%) encountered: a hemothorax (n = 1) and a bronchopleural fistula (n = 1). CONCLUSION: Although RFA using a monopolar wet electrode can create a large ablation zone, it is associated with a high rate of technical failure when used to treat inoperable non-small cell lung malignancies.

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.

Complications Following Radiofrequency Ablation of the Porcine Liver through Portal Vein Penetration: Radiological Findings

PURPOSE: To evaluate complications after radiofrequency ablation (RFA) of the porcine liver through portal vein penetration. MATERIALS AND METHODS: Twelve pigs were divided into two groups. In group I (n=11) animals, the portal veins were directly penetrated with an electrode, and in the group II (n=16) animals, the portal veins were located within the expected ablation area. For the group I pigs, RFA were performed for seven minutes after complete portal vein passing of the exposed tip. Gray-scale and Doppler ultrasonography, and CT were performed before and after RFA on the procedure day, and on day two. If any complications were found, the same studies were performed at day seven. We analyzed the presence and extent of thrombotic occlusion, the vascular stricture, the arterioportal shunt, and the presence of an intra-abdominal hemorrhage. We applied Fisher's exact test to compare the complication rate between the two groups;, a value was considered statistically significant if the p-value was less than 0.05. RESULTS: In the group I animals (n=11), three had complete thrombotic occlusion of the portal vein. Among these three animals,, one had a segmental infarction, and one animal showed a partial occlusion. In the group II animals (n=16), complications were not identified. Statistical analysis revealed the complication rate of group I was significantly higher than that of group II (p=.019). CONCLUSION: The portal vein occlusion rate was significantly higher in the portal vein penetrating group than in the non-penetrating group.

A Metastatic Adrenal Tumor from a Hepatocellular Carcinoma: Combination Therapy with Transarterial Chemoembolization and Radiofrequency Ablation

The adrenal gland is the second most common site of metastasis from a hepatocellular carcinoma (HCC). Radiofrequency ablation (RFA) for these tumors has been reported to be a potentially effective alternative to an adrenalectomy, especially for inoperable patients. However, for intermediate or large adrenal tumors, combination therapy of transarterial chemoembolization (TACE) and RFA can be attempted as it may reduce the heat sink effect. A 74-year-old patient presented with abdominal discomfort. Abdominal CT images revealed a 5.0 cm sized right adrenal mass. A percutaneous biopsy of the adrenal mass revealed a metastatic hepatocellular carcinoma. TACE was performed on the adrenal mass. However, a one-month follow-up CT image revealed a residual viable tumor. RFA was performed for the adrenal tumor six weeks after the TACE. No procedure-related major complications were noted. The serum alpha-fetoprotein level had also been normalized after the treatment, and 10-month follow-up CT images showed no definite evidence of viable adrenal tumor.

Comparison of Radiofrequency Ablation Lesion Size with Occlusion of Renal Vessels in Rabbit Kidneys: Occlusion of Renal Artery, Vein, and Both Vessels

PURPOSE: The purpose of this study was to compare the in-vivo efficiency of vascular occlusion on radiofrequency ablation (RFA) lesion size in a rabbit kidney model. MATERIALS AND METHODS: RFA lesions were created in a single kidney in 20 rabbits using an internally cooled electrode. Twenty ablation zones (1 per kidney) were created using 4 different regimens: RFA without vascular occlusion (n = 5), RFA with renal artery occlusion (n = 5), RFA with renal vein occlusion (n = 5), RFA with renal artery and vein occlusion (n = 5). Seven days later, the rabbits were sacrificed and the lesions were excised. These groups were then compared with respect to the dimensions of the ablation zones and the changes in impedance and current during RFA. RESULTS: The maximum ablation zone width was the greatest in the renal artery and vein occlusion group (21.0+/-1.4 mm), followed by the renal artery occlusion group (17.8+/-1.0 mm), the renal vein occlusion group (17.4+/-1.1 mm), and the nonocclusion group (7.8+/-2.4 mm) (p < 0.05). No significant differences were observed for impedances and currents between the 4 groups. CONCLUSION: Vascular occlusion combined with RFA effectively increased ablation zone dimensions compared with RFA alone, and the best effect was accomplished by combined renal artery and vein occlusion.

Ferucarbotran-Enhanced MR Imaging of the Radiofrequency Ablation Zones in the Normal Rabbit Liver: Comparison with the Conventional MR Imaging

PURPOSE: We wanted to evaluate the findings of ferucarbotran-enhanced MR imaging of the radiofrequency (RF) ablation zones in normal rabbit livers and we compared the findings with the conventional MR imaging. MATERIALS AND METHODS: RF ablation zones were created in the livers of 12 rabbits in vivo by using a 17-gauge internally cooled electrode with 1-cm active tip, and RF energy (maximum power: 30 Watt) was applied for three minutes. Three rabbits were sacrificed immediately and then at three days, two weeks and six weeks after RF ablation. Before sacrifice, the T1- and T2-weighted images (WI) and the ferucarbotran-enhanced T2*WIs were obtained and compared regarding the signal intensity of ablation zone, the laminar pattern of the signal intensity and the contrast-to-noise ratio (CNR) of the ablation zone to the liver parenchyma. RESULTS: On T1- and T2WIs, the RF ablation zones showed two to four laminar patterns of signal intensity according to the time. Meanwhile, on the ferucarbotran-enhanced T2WIs, the RF ablation zones showed high signal intensity without a laminar pattern regardless of time. The CNRs of the ablation zones to the liver parenchyma on the ferucarbotran-enhanced T2*WIs (18.2+/-5.9) were significantly higher than those of the TIWIs (1.6+/-1.5) and T2WIs (2.7+/-1.9) (p < 0.05). CONCLUSION: On the ferucarbotran-enhanced T2*WI, the RF ablation zones showed high signal intensity without a distinct laminar pattern and significantly higher lesion conspicuity than did the conventional T1- and T2WIs. Therefore, the ferucarbotran-enhanced T2*WI shows the RF ablation zone more accurately and clearly than do the conventional T1- and T2WIs.

Radiofrequency Neurotomy of the Medial Branch for the Management of Lumbar Zygapophysial Joint Pain

PURPOSE: We wanted to investigate the efficacy of percutaneous radiofrequency (RF) neurotomy of the medial branch for the management of chronic low back pain due to lumbar zygapophysial joint dysfunction. MATERIALS AND METHODS: Thirteen patients who had unremitting chronic low back pain for more than 6 months and whose VAS scores were over 7 were selected on the basis of double comparative nerve blocks. The patients consist of three males and 10 females, and their nean age was 67 years. Sensory stimulation was performed to detect the "pathologic branches" that were responsible for pain generation. RF neurotomy was performed using a lesion generator at 80 C for 90 seconds. The postoperative outcome was classified, depending on the degree of pain reduction, as excellent (> or = 75%), good (50-75%), and poor (<50%). Follow-up evaluation was performed at 6 weeks, 3 months and 6 months after surgery. RESULTS: The mean number of medial branches was 6.2. Eleven patients had bilateral disease and two had unilateral disease. Sensory stimulation was positive in all patients with a mean amplitude of 4.5V (range: 0.15-6 V). The L5 dorsal ramus was the most frequently involved segment, and this was followed by L4, L3 and L2. The number of lesionings for each medial branch was 3.7. The surgical outcome was graded as excellent (53%), good (23%), and poor (24%) after 6 months of follow-up. Transient backaches were noticed in two patients; however, complications were not observed. Recurrences were not demonstrated during the follow-up period CONCLUSION: We conclude that RF neurotomy of the medial branches is an efficient method to substantially alleviate the chronic low back pain caused by zygapophysial joint dysfunction.

Radiofrequency Ablation of Hepatic Cysts: Case Report

Radiofrequency ablation has been frequently performed on intra-hepatic solid tumor, namaly, hepatocellular carcinoma, metastatic tumor and cholangiocarcinoma, for take the cure. But, the reports of radiofrequency ablation for intrahepatic simple cysts are few. In vitro experiment of animal and in vivo treatment for intrahepatic cysts of human had been reported in rare cases. We report 4 cases of radiofrequency ablation for symptomatic intrahepatic cysts.

Feasibility of Saline Infusion on the Liver Surface during Radiofrequency Ablation of Subcapsular Hepatic Tumor: An Experimental Study

PURPOSE: The purpose of the study was to evaluate the feasibility of infusion of normal saline onto the surface of the liver capsule for minimizing thermal injury of the adjacent organs during radiofrequency ablation of subcapsular hepatic tumor in an ex-vivo porcine model. MATERIALS AND METHODS: We used porcine small bowel with it's serosal surface spread onto the porcine liver as an experiment model. The puncturing electrode was inserted into a 6 Fr introducer sheath, and the introducer sheath was connected to the infusion pump for creating a saline flow over the liver surface . A total of 15 ablations were divided into the control group (n=5), intermittent saline infusion group (n=5) and continuous saline infusion (n=5) group. The ablations were done during 3 minutes, and the infusion was set at 2 ml/min and stopped every 30 seconds in the intermittent saline infusion group. After the ablation, we measured the size of the ablated lesion on the surface of bowel and liver, and we also measured the depth of hepatic lesion. RESULTS: Ablated areas of bowel and liver surface in the control group, intermittent saline infusion group and continuous infusion group were 210.7+/-89.1 mm2, 74.6+/-27.2 mm2 and 35.8+/-43.4 mm2, respectively, and 312.6+/-73.6 mm2, 228.4+/-110.5 mm2, and 80.9+/-55.1 mm2, respectively. In contrast to the broad base of the ablated area on the surface of the liver in the control group, the shapes of the lesions became narrower approaching to the liver surface in all cases of the continuous saline infusion group, and the shapes of the lesions were broad based in 3 cases and narrow based in 2 cases of the intermittent saline infusion group. CONCLUSION: Continuous infusion of normal saline onto the surface of the liver during radiofrequency ablation of subcapsular hepatic tumor is a feasible method for minimizing thermal injury of the adjacent organs. Further exploration of the optimal parameters or techniques to maximize the hepatic ablation and simultaneously to minimize the thermal injury of adjacent organs is required.

Radio-frequency Ablation in Patients with Malignant Hepatic Tumor and Experimental Model: Comparison of Expandable Needle and Water-Cooled Needle

PURPOSE: The purpose of this study was to compare the shape and volume of the radio-frequency induced lesions produced by two commercially available radio-frequency ablation (RFA) systems, the expandable and cooled-tip needles, in clinical patients and an experimental model. MATERIALS AND METHODS: A twelve-array anchor expandable needle electrode and a single cooled-tip needle electrode were used to treat hepatic tumors with a single session in 23 patients (20 hepatocellular carcinomas and 3 hepatic metastases) and fourteen patients (10 hepatocellular carcinomas and 4 hepatic metastases), respectively. Twenty RFA induced lesions were created with each system in 10 explanted bovine livers. The shape of the RFA induced lesions were divided into oval lesions along or perpendicular to the axis of the electrode and spherical lesions, and we then calculated the volumes of the RFA induced lesions. RESULTS: Fourteen (61%) lesions of the 23 patients treated with the expandable system were oval perpendicular to the axis of the electrode and nine (39%) of the lesions were spherical. All the lesions (100%) of the 14 patients treated with the cooled-tip needle were oval along the axis of the electrode. In the ex vivo bovine livers, the shape of the all RFA induced lesions was oval perpendicular to the axis of the electrode for the expandable needle, and oval along the axis of the electrode for the cooled-tip needle. The mean diameter and volume of the RFA induced lesions in the patients were 3.35+/-0.56cm and 19.9+/-6.53 cm3, respectively, for the expandable needle and 3.58+/-0.78 cm and 23.19+/-5.27 cm3, respectively, for the cooled-tip needle. In the ex vivo model, the mean diameter and volume of RFA induced lesions were 3.41+/-0.59 cm and 26.59+/-8.02 cm3, respectively, for the expandable needle, and 4.04+/-0.65 cm and 33.82+/-6.16 cm3, respectively, for the cooled-tip needle (p<0.05). CONCLUSION:These results indicate that the shape of RFA induced lesions with the expandable needle were oval perpendicular to the axis of the electrode but those with the cooled-tip needle were oval along the axis of the electrode in both the clinical and experimental models. The cooled-tip needle induced significantly larger lesions than the expandable needle in the clinical patients and the experimental model. We need to consider these characteristic findings for RFA when we are performing such procedures.

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.

Percutaneous Radiofrequency Ablation of Inoperable Primary Lung Cancer

PURPOSE: To present the initial experience of percutaneous radiofrequency ablation (RFA) of inoperable primary lung cancer, and to assess the technical feasibility and potential complications. MATERIALS AND METHODS: Twenty patients with inoperable lung cancer underwent percutaneous RFA. Nineteen of 20 patients had stage III or IV non-small cell lung cancer, and the remaining one had stage I lung cancer with pulmonary dysfunction. The mean tumor size was 4.6+/-0.4 cm (range, 1.8-8.4 cm). RFA was performed with a single (n=18) or cluster (n=2) cool-tip RF electrode and a generator under CT guidance using local anesthesia and conscious sedation. Twenty tumors were treated in 28 sessions. Patients were assessed by contrast-enhanced CT in all cases at 1 week, 1 month, and 3 months. Eleven patients received chemotherapy (n=10) or radiotherapy (n=1) after RFA. RESULTS: RFA was technically successful and well tolerated in all patients. Complete necrosis was attained in 7 lesions (35%), near complete (90-99%) necrosis in 10 lesions (50%), and partial (50-89%) necrosis in 3 lesions (15%). During the mean follow up of 202 days (21 to 481 days), tumor size was decreased in 13 patients, unchanged in 3, and increased in 4. In the latter four, additional RFA was performed. One patient underwent surgery three months after RFA and the histopathologic findings showed a large cavity with thin fibrotic wall suggestive of complete necrosis. During or after the procedure, pneumothorax (n=10), moderate pain (n=4), blood tinged sputum (n=2), and pneumonia (n=2) were developed. Chest tube drainage was required in only 1 patient due to severe pneumothorax. Other patients were managed conservatively. Seven patients died at 61 to 398 days (mean, 230 days) after RFA. The remaining 13 patients were alive 21 to 481 days (mean, 187 days) after RFA. CONCLUSION: RFA appears to be a technically feasible and relatively safe procedure for the cytoreductive treatment of inoperable, non-small cell lung cancer and warrants further investigation as a complementary treatment to chemotherapy or radiation therapy.

Endovenous Radiofrequency Ablation using Stent-type Electrode for Varicose Veins: an Experimental Study in Goats

PURPOSE: The purpose of this study was to investigate the feasibility and the optimal conditions of radiofrequency (RF) ablation by using the stent-type electrode upon the saphenous vein of goats for the endovenous treatment of varicose veins. MATERIALS AND METHODS: A self-expandable nitinol stent electrode (6 mm diameter, 2 cm length, cell size; 1.3x2 mm) was designed to expose the distal 1cm segment to allow for contact with the venous wall. The proximal part of the electrode was connected to the RF generator by insulated copper wires located within the stent electode introducer. Initially, to optimize the power setting, ablation of 6 saphenous veins in 3 goats was performed with power settings of 10, 20 and 30 W. Pull back rate of the electrode was 2 and 4 cm/min for each power level, respectively. The goats were sacrificed 4-6 weeks later and histologic examinations of the saphenous veins were done. For the second part of the experiment, RF ablation of 4 saphenous veins from 2 goats was done by applying the optimal power, based upon the first examination; these procedure was performed with variable pull back rates. Again, the goats were sacrificed 1-6 weeks later and histologic examinations were done. RESULTS: Endovenous ablation of the goat saphenous veins at 20 W caused complete obliteration without complication. There was incomplete occlusion at 10 W, and there were vessel perforation, extravasation, and adjacent tissue injury at 30 W. In second part of the study, the complete circumferential obliteration of the vein was demonstrated at a pull back rate of 1 cm/min and 3 cm/min with the power of 20 W. CONCLUSION: The stent-type electrode may be useful in endovenous RF ablation for treatment of varicose veins. For stents with a diameter of 6 mm, the optional combination of 20 W of power with a pull back rate of 1-3 cm/min produced the most favorable results. Further study and clinical investigations are warranted.

Radiofrequency Ablation of Liver Cancer: Early Evaluation of Therapeutic Response with Contrast-Enhanced Ultrasonography

The early assessment of the therapeutic response after percutaneous radiofrequency (RF) ablation is important, in order to correctly decide whether further treatment is necessary. The residual unablated tumor is usually depicted on contrast-enhanced multiphase helical computed tomography (CT) as a focal enhancing structure during the arterial and portal venous phases. Contrast-enhanced color Doppler and power Doppler ultrasonography (US) have also been used to detect residual tumors. Contrast-enhanced gray-scale US, using a harmonic technology which has recently been introduced, allows for the detection of residual tumors after ablation, without any of the blooming or motion artifacts usually seen on contrast-enhanced color or power Doppler US. Based on our experience and reports in the literature, we consider that contrast-enhanced gray-scale harmonic US constitutes a reliable alternative to contrast-enhanced multiphase CT for the early evaluation of the therapeutic response to RF ablation for liver cancer. This technique was also useful in targeting any residual unablated tumors encountered during additional ablation.

Radiofrequency Ablation of Rabbit Liver In Vivo: Effect of the Pringle Maneuver on Pathologic Changes in Liver Surrounding the Ablation Zone

OBJECTIVE: We wished to evaluate the effect of the Pringle maneuver (occlusion of both the hepatic artery and portal vein) on the pathologic changes in the hepatic vessels, bile ducts and liver parenchyma surrounding the ablation zone in rabbit livers. MATERIALS AND METHODS: Radiofrequency (RF) ablation zones were created in the livers of 24 rabbits in vivo by using a 50-W, 480-kHz monopolar RF generator and a 15-gauge expandable electrode with four sharp prongs for 7 mins. The tips of the electrodes were placed in the liver parenchyma near the porta hepatis with the distal 1 cm of their prongs deployed. Radiofrequency ablation was performed in the groups with (n=12 rabbits) and without (n=12 rabbits) the Pringle maneuver. Three animals of each group were sacrificed immediately, three days (the acute phase), seven days (the early subacute phase) and two weeks (the late subacute phase) after RF ablation. The ablation zones were excised and serial pathologic changes in the hepatic vessels, bile ducts and liver parenchyma surrounding the ablation zone were evaluated. RESULTS: With the Pringle maneuver, portal vein thrombosis was found in three cases (in the immediate [n=2] and acute phase [n=1]), bile duct dilatation adjacent to the ablation zone was found in one case (in the late subacute phase [n=1]), infarction adjacent to the ablation zone was found in three cases (in the early subacute [n=2] and late subacute [n=1] phases). None of the above changes was found in the livers ablated without the Pringle maneuver. On the microscopic findings, centrilobular congestion, sinusoidal congestion, sinusoidal platelet and neutrophilic adhesion, and hepatocyte vacuolar and ballooning changes in liver ablated with Pringle maneuver showed more significant changes than in those livers ablated without the Pringle maneuver (p < 0.05) CONCLUSION: Radiofrequency ablation with the Pringle maneuver created more severe pathologic changes in the portal vein, bile ducts and liver parenchyma surrounding the ablation zone compared with RF ablation without the Pringle maneuver. Therefore, we suggest that RF ablation with the Pringle maneuver should be performed with great caution in order to avoid unwanted thermal injury.

Transluminal Radio-Frequency Thermal Ablation Using a Stent-Type Electrode: an Experimental Study

PURPOSE: To assess the feasibility of transluminal radiofrequency thermal ablation using a stent-type electrode and to determine, by means of in-vitro and in-vivo animal studies, the appropriate parameters. MATERIALS AND METHODS: In vitro: The radiofrequency electrode used was a self-expandable nitinol stent with 1cm insulated ends. A stent was placed in the portal vein of bovine liver, and ablations at target temperatures of 70, 80, 90, and 100degrees C were performed. Ablated sizes were measured longitudinally. In vivo: Four mongrel dogs were anesthetized, and a stent was inserted in the common bile duct under fluoroscopic guidance through an ultrasound-guided gall bladder puncture site. The ablation temperature was set at 80 degrees C, and each dog underwent proximal and distal esophageal ablations lasting 12 minutes. They were sacrificed immediately. RESULTS: In-vitro: Ablated sizes showed significant correlation with target temperatures (r>0.04; p<0.05). Although most lesions were fusiform, dumbbell-shaped lesions with central thinning were found in two cases in the 70degrees C group. In all cases in the 70 degrees C and 80 degrees C group, the length of the insulated segment was less than 1 cm. In-vivo: At microscopy, tissues at the center of the biliary stent showed more prominent pathological change than those at the periphery while those remote from the stent showed minimal or no change. In esophageal ablations, the mean highest temperature was 48.6 degrees C. Microscopy demonstrated the destruction and shedding of mucosa, edema, and coagulation necrosis of submucosa, but in muscle layers no abnormalities were apparent. CONCLUSION: Transluminal radio-frequency thermal ablation using a stent-type electrode may be useful for elongating patency. The appropriate target temperature for biliary ablation is 80 degrees C.

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.