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℃ in group W and 33.4±4.3℃ 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.     

Radiofrequency ablation of the liver abutting stomach: in vivo comparison of gastric injury before and after intragastric saline administration in a porcine model

Purpose

To compare the in vivo gastric injury observed during radiofrequency (RF) ablation of the liver abutting the stomach before and after the intragastric administration of chilled saline.

Materials and methods

Twenty RF ablation zones were created in the livers of 10 pigs with a 1-cm-exposed active tip of an internally cooled electrode under ultrasound guidance for 10 min. Ten RF ablation zones were created before (non-saline group) and after (saline group) the intragastric administration of approximately 1000 mL of chilled saline, and 20 RF ablation zones were made in the posterior part of the left lobe abutting the stomach. The frequency and severity of the thermal injury observed in the stomach of the two groups were compared histologically.

Results

All the resected gastric specimens showed thermal injuries of varying degrees of severity. The largest diameter of the gastric injury was significantly smaller in the saline group (mean 1.5 cm; range 1.3-1.8 cm) than in the non-saline group (mean 2.1 cm; range 1.8-2.4 cm) (p = 0.000). The saline group showed significantly less thermal injury to the muscular layer of the gastric wall by the histopathology (p = 0.033).

Conclusions

The intragastric administration of chilled saline might be a useful technique for reducing the severity of gastric injury during RF ablation of the liver abutting the stomach.     

Minimizing diaphragmatic injury during radio-frequency ablation: efficacy of subphrenic peritoneal saline injection in a porcine model

PURPOSE: To investigate if a targeted subphrenic peritoneal infusion of normal saline to separate liver from diaphragm before radio-frequency (RF) ablation could minimize or eliminate diaphragmatic injury. MATERIALS AND METHODS: With a 2-cm-diameter, eight-prong RF needle electrode, 37 hepatic dome RF lesions were created in 10 pigs. Seventeen lesions were created before (non-saline group) and 20 lesions after (post-saline group) intraperitoneal infusion of approximately 500 mL of normal saline. Ten non-saline lesions were created deep (centered 1-2 cm from the liver surface) and seven superficially (centered within 1 cm of the capsule). All 20 post-saline lesions were created superficially. Helical enhanced computed tomography was performed 24-48 hours after ablation. The pigs were killed immediately, and the diaphragm was visually inspected and sectioned. Diaphragmatic injury was graded as 0, no injury; 1, injury up to one-third thickness; 2, injury to two-thirds thickness; 3, full-thickness injury. Representative grade 3 injuries and all partial injuries underwent gross and histologic analysis. RESULTS: All 10 deep non-saline RF lesions caused grade 0 injury. All seven superficial non-saline lesions caused grade 3 injury. Of the 20 superficial post-saline lesions, 13 (65%) caused grade 0 injury; four (20%), grade 1; and three (15%), grade 3. The post-saline group caused significantly less diaphragmatic injury (P <.05). CONCLUSION: Intraperitoneal saline infusion may reduce the frequency and severity of diaphragmatic injury when adjacent liver is treated with RF ablation.     

Guidewire-catheter induced hydrodissection to assist radiofrequency ablation for subcapsular hepatocellular carcinoma with iodized oil retention in patients with failed artificial ascites due to perihepatic adhesion

PURPOSEWe aimed to evaluate the usefulness of guidewire-catheter induced hydrodissection (GIH) to assist radiofrequency ablation (RFA) for subcapsular hepatocellular carcinoma (HCC) with iodized oil retention in patients with failed artificial ascites due to perihepatic adhesion.METHODSThis retrospective study included 17 patients with small subcapsular HCC ineligible for ultrasonography-guided RFA who received RFA under guidance of fluoroscopy and cone-beam computed tomography immediately after iodized oil transarterial chemoembolization (TACE) between April 2011 and January 2016. In the study patients, creation of artificial ascites to protect the perihepatic structures failed due to perihepatic adhesion and GIH was attempted to separate the perihepatic structures from the ablation zone. The technical success rate of GIH, technique efficacy of RFA with GIH, local tumor progression (LTP), peritoneal seeding, and complications were evaluated.RESULTSThe technical success rate of GIH was 88.24% (15 of 17 patients). Technique efficacy was achieved in all 15 patients receiving RFA with GIH. During an average follow-up period of 48.1 months, LTP developed in three patients. Cumulative LTP rates at 1, 2, 3, and 5 years were 13.3%, 20.6%, 20.6%, and 20.6%, respectively. No patient had peritoneal seeding. Two of the 15 patients receiving RFA with GIH had a CIRSE grade 3 liver abscess, but none had complications associated with thermal injury to the diaphragm or abdominal wall near the ablation zone.CONCLUSIONGIH can be a useful method to assist RFA for subcapsular HCC with iodized oil retention in patients with failed artificial ascites due to perihepatic adhesion.

Radiofrequency ablation (RFA) is widely accepted as a curative treatment for patients with small (≤3 cm) hepatocellular carcinoma (HCC) not suitable for surgery (1, 2). However, when the tumor is located close to the liver surface, RFA carries a risk of unintended collateral thermal injury to the perihepatic structures (i.e., diaphragm and abdominal wall). To overcome this problem, adjunctive techniques such as introduction of artificial ascites or pleural effusion have been applied (3–8). Nonetheless, patients with perihepatic peritoneal adhesion may still be at risk of collateral thermal injury as adhesion prevents separation of the perihepatic structures by artificial ascites from the ablation zone (6, 9, 10). Some investigators have used an alternative technique making localized hydrodissection by using an 18–22 G needle at the contact point between the index tumor and perihepatic structure (9, 11). However, this also seems to be not applicable when the lung or bowel interposes on the access route.Prior iodized oil transarterial chemoembolization (TACE) enhances the feasibility of subsequent RFA for small tumors with poor conspicuity (12, 13). This is because intratumoral retention of radio-opaque iodized oil provides radiographic contrast to the index tumor. As the index tumor with iodized oil retention is clearly seen on fluoroscopy and the perihepatic peritoneal space is easily accessed by traditional methods of making artificial ascites (6, 9, 14), an angiographic catheter and guidewire system can reach the region near the tumor through the perihepatic space under fluoroscopic guidance. Therefore, in patients with perihepatic adhesion, if forceful advancement of the catheter and guidewire system could dissect the adhesion, introduction of fluid via the catheter tip at the region near the tumor may protect the perihepatic structures from thermal injury during RFA for subcapsular HCC.The aim of this study was to evaluate the usefulness of guidewire-catheter induced hydrodissection (GIH) to assist RFA for subcapsular HCC with iodized oil retention in patients with failed artificial ascites due to perihepatic adhesion.     

Percutaneous radiofrequency ablation of hepatocellular carcinoma abutting the diaphragm and gastrointestinal tracts with the use of artificial ascites: safety and technical efficacy in 143 patients

The purpose of this study was to assess the feasibility, safety and efficacy of radiofrequency ablation (RFA) with the use of artificial ascites for hepatocellular carcinoma (HCC) adjacent to the diaphragm and gastrointestinal tract. One hundred forty-three patients with 181 HCCs who underwent US-guided percutaneous RFA with the use of artificial ascites were retrospectively reviewed. Among the 181 HCCs, 148 HCCs were defined as problematic nodules for two major reasons: poor sonic window or possible thermal injury. We artificially induced ascites before performing RFA by dripping 5% dextrose in a water solution. We assessed the technical success of introducing artificial ascites, technical feasibility of the use of artificial ascites and complications. The technical success rate, as well as the primary and secondary technique success rate, was assessed by regular follow-up CT examinations. RFA with artificial ascites was successfully achieved in 130 of 143 patients. The primary technique effectiveness was 85.3%. During follow-up (mean, 20.4 months), remote intrahepatic recurrence occurred in 49 patients and local tumor progression occurred in 15 patients. Three (2.1%) of the 143 patients experienced major complications (hemoperitoneum, lobar infarction and biloma) related to the RFA procedure. The use of artificial ascites is a simple and useful technique to minimize collateral thermal injury and to improve the sonic window.     

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.     

Lung radiofrequency ablation with and without bronchial occlusion: experimental study in porcine lungs

PURPOSE: This study was undertaken to compare the thermal lesion volumes in normal pig lungs when radiofrequency (RF) ablation is performed with and without airway occlusion. MATERIALS AND METHODS: RF ablation was performed in six pigs. A straight 17-gauge internally cooled-tip electrode with a 2-cm exposed tip was inserted into the center of the lower lobe of the lung under biplane fluoroscopic guidance. In each animal, RF ablation was performed for 12 minutes with balloon occlusion of the main bronchus in one lung and without balloon occlusion in the contralateral lung. The tissue temperature around the electrode tip was measured immediately after RF application. The volumes of the thermal lesions were compared by histologic examination of the groups of lungs ablated with and without airway occlusion. RESULTS: Tissue temperature was significantly higher in the bronchial occlusion group than in the group with normal ventilation (51 degrees C +/- 7 vs. 44 degrees C +/- 2; P < .05). RF ablation with bronchial occlusion resulted in the creation of a significantly greater thermal lesion volume compared with RF ablation with normal ventilation (6,535 mm(3) +/- 1,114 vs 3,368 mm(3) +/- 676; P < .03). CONCLUSION: Prevention of ventilation in the normal swine lung via bronchial balloon occlusion during RF ablation increases the thermal ablation lesion volume, suggesting that active ventilation is a significant cause of in vivo heat loss.     

Ultrasound-Guided Percutaneous Radiofrequency Ablation of Liver Tumors: How We Do It Safely and Completely

Ultrasound-guided percutaneous radiofrequency (RF) ablation has become one of the most promising local cancer therapies for both resectable and nonresectable hepatic tumors. Although RF ablation is a safe and effective technique for the treatment of liver tumors, the outcome of treatment can be closely related to the location and shape of the tumors. There may be difficulties with RF ablation of tumors that are adjacent to large vessels or extrahepatic heat-vulnerable organs and tumors in the caudate lobe, possibly resulting in major complications or treatment failure. Thus, a number of strategies have been developed to overcome these challenges, which include artificial ascites, needle track ablation, fusion imaging guidance, parallel targeting, bypass targeting, etc. Operators need to use the right strategy in the right situation to avoid the possibility of complications and incomplete thermal tissue destruction; with the right strategy, RF ablation can be performed successfully, even for hepatic tumors in high-risk locations. This article offers technical strategies that can be used to effectively perform RF ablation as well as to minimize possible complications related to the procedure with representative cases and schematic illustrations.     

Combined radiofrequency ablation and hot saline injection in rabbit liver

RATIONALE AND OBJECTIVES: To determine whether combining hot saline injection (HSI) and radiofrequency ablation (RFA) can increase the extent of thermally mediated coagulation in in vivo rabbit liver tissue. METHODS: In 66 rabbits, RF energy and/or hot saline-induced coagulations were produced using a 17-gauge cooled electrode or 21-gauge needle under ultrasound guidance. Rabbits were allocated into 1 of 5 groups: group A, RFA alone (n = 15); group B, HSI (1 mL hot saline infused, n = 10); group C, combined therapy for HSI followed by RFA (n = 21); group D, combined therapy for RFA immediately followed by HSI (n = 10); and group E, 1 mL room temperature saline infusion before RFA (n = 10). RF energy (30 W) was applied for 3 minutes. The changes in tissue impedance, current, power output, and temperature of the electrode tip were automatically measured. Before RFA, precontrast computed tomography was performed, and after RFA, pre- and postcontrast spiral computed tomographic scans were acquired. The maximum diameters of the thermal lesions on the gross specimens and complications of each group were compared. RESULTS: All procedures were technically successful. There were 9 of 61 procedure-related complications (14.8%) including 6 localized hematomas and 3 thermal injuries to the diaphragm and the stomach. In rabbits in groups C and E, a marked decrease of tissue impedance (43.4 omega, 44.1 omega) and an increase of current (709 mA, 722 mA) occurred with instillation of saline infusion compared with RFA only. Combined therapy for HSI followed by RFA produced a greater short-axis mean diameter of coagulation (14.6 +/- 4.3 mm) than that in rabbits of other groups, for RFA only (10.4 +/- 2.4 mm), HSI only (8.7 +/- 3.3 mm), and combined therapy for RFA immediately followed by HIS (12.0 +/- 1.4 mm; P < 0.05). CONCLUSION: Combined therapy for HSI followed by RFA can increase the volume of RFA-induced coagulation in the liver with a single application, and therefore may improve the results of RFA for the treatment of larger tumors.     

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.     

Combined treatment of radiofrequency ablation and acetic acid injection: an in vivo feasibility study in rabbit liver

The aim of this study was to compare the effects of percutaneous radiofrequency ablation (RFA) combined with percutaneous acetic acid injection (PAI) and either therapy alone for their effects on in vivo rabbit liver tissue. Thirty New Zealand white rabbits were included in this study and were allocated to three groups: group A, conventional RFA (n=10); group B, PAI (n=10); and group C, combined RFA and PAI (n=10). Under US guidance, 1 ml of 50% acetic acid was injected into the target area of the liver parenchyma through a 21-G Chiba needle before performing RFA. The RFA was then performed using a 17-G internally cooled electrode with 1-cm active tip, and RF energy (30 W) was applied for 3 min with or without acetic acid injection. After RFA or PAI, contrast-enhanced CT and CT pathologic correlation were performed. The maximum diameters of the thermal lesions in each group were compared. All procedures were technically successful, and a total of 30 lesions (10 lesions for each group) were produced. The mean maximum diameter of the coagulation necrosis in the rabbits of group C (25±9 mm) was significantly larger than the diameters of the other groups: 12.2±1 mm (group A) and 14.3±3 mm (group B; p=0.001). On contrast-enhanced CT scanning, the lesions of group B (7 of 10, 70%) appeared frequently irregular compared with those of groups A (2 of 10, 20%) and C (4 of 10, 40%; p=0.08). There were seven complications (23.3%): a localized hematoma in a group-A rabbit; two hematomas and one chemical peritonitis in group-B rabbits; and a hematoma, a chemical peritonitis, and a burn injury to the stomach in group-C rabbits. Compared with the group-A rabbits (1 of 10, 10%), the group-B (3 of 10, 30%) and group-C rabbits (3 of 10, 30%) showed a tendency toward complications, but the difference was not significant (p=0.48). Under the present experimental condition, combined RFA and PAI was able to increase the diameter of coagulation necrosis up to 2.5 cm without significantly increasing complications.     

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.     

Efficacy and safety of radiofrequency ablation of hepatocellular carcinoma in the hepatic dome with the CT-guided extrathoracic transhepatic approach

PURPOSE: The purpose of this study was to determine the efficacy and safety of radiofrequency (RF) ablation for the treatment of hepatocellular carcinoma (HCC) in the hepatic dome with CT-guided extrathoracic transhepatic approach. MATERIALS AND METHODS: Fifteen patients with 15 HCCs (size range: 0.8-4 cm, mean size: 1.8 cm) in the hepatic dome were treated by RF ablation using cooled-tip electrodes and with CT-guided extrathoracic transhepatic approach. Therapeutic response of the tumor to RF ablation and procedure-related complications including hepatic injury, hemoperitoneum, and thermal injury of diaphragm were evaluated. RESULTS: The average number of needle punctures to ensure the correct needle position in the targeted tumor was 3.7 (range: 1-6 punctures). The average ablation time was 14.7 min (range: 8-25 min). Complete necrosis without marginal recurrence after at least 13-month follow-up was attained in 13 tumors (86.7%). There were no major complications related to the procedures. Six patients had shoulder pain that lasted three days to two weeks after the procedures and their symptoms were resolved with conservative treatment. CONCLUSIONS: RF ablation using CT-guided extrathoracic transhepatic approach is an effective and safe technique for the treatment of HCC in the hepatic dome.     

How does alteration of hepatic blood flow affect liver perfusion and radiofrequency-induced thermal lesion size in rabbit liver?

The purpose of this study was to test the hypothesis that decreasing liver perfusion in rabbits results in an increase in thermal lesion size and that these effects can be accurately monitored using magnetic resonance imaging (MRI). We additionally tested the hypothesis that the increase in thermal lesion size would depend on the particular vessel or vessels occluded (hepatic artery, portal vein, or both). Using an Institutional Animal Care and Use Committee approved protocol, 20 New Zealand white rabbits were randomly assigned to four treatment groups (five in each group): control and ligation of portal vein (PV), hepatic artery (HA), or both PV and HA (HAPV). Surgical ligation of the appropriate vessel was performed under general anesthesia. Immediately after ligation, the rabbits were placed in a 0.2-T open MR system, and an 18-G copper radiofrequency (RF) electrode with a 2-cm exposed tip was inserted into the liver. RF was applied for 10 minutes with the tip temperature maintained at 90 degrees +/- 2 degrees C. Before and after ablation, perfusion data were obtained for 90 seconds using 30 3-second sequential single oblique-slice fast imaging with steady-state progression (FISP) acquisitions after injection of gadolinium-diethylene triamine pentaacetic acid (Gd-DTPA) via the inferior vena cava. Postablation scanning included axial and oblique turbo spin-echo (TSE) T2-weighted (T2w), STIR, and Gd-enhanced T1w sequences. Lesion size was determined perpendicular to the RF electrode using software calipers on the imager. The rabbits were sacrificed after completion of the post-therapy scans, and their livers were harvested for histologic analysis. The liver showed a mean increase in signal amplitude (SA) of 76% 24 seconds after Gd contrast injection in the control group. After contrast injection, the SA increased to a mean of only 66% in the group with ligated hepatic arteries, with no difference in the time to peak compared with the control group. No significant SA increase over baseline could be found in the groups with ligated PV or ligated PV and HA. T2-weighted images demonstrated the highest lesion-to-liver contrast-to-noise ratios (CNRs; mean -5.5) on postprocedure images, followed by STIR images (mean -2.2) in the control group. The lesions were poorly delineated on the Gd-enhanced images. Average maximum lesion sizes (mean +/- 95% confidence interval) were 22 +/- 4.3 mm after ligation of PV, 22 +/- 2.6 mm after ligation of both PV and HA, 14 +/- 2.0 mm after ligation of HA, and 13 +/- 1.9 mm in the control group. We accept the hypothesis that the diameter of the region of coagulation necrosis achieved by standardized RF ablation in the liver increases with reduced organ perfusion and that this effect can be accurately monitored using MRI. The major factor influencing the size of the coagulation area is the portal venous flow. Occlusion of the hepatic artery alone does not significantly increase lesion size. T2w sequences are best suited for postprocedure imaging due to the high lesion-to-liver CNR in rabbits with normal hepatic perfusion. J. Magn. Reson. Imaging 2001;13:57-63.     

Placement of a Sodium Hyaluronate Solution onto the Liver Surface as a Supportive Procedure for Radiofrequency Ablation of Hepatocellular Carcinomas Located on the Liver Surface: A Preliminary Report

PurposeTo evaluate safety and efficacy of the placement of sodium hyaluronate solution onto the liver surface as a supportive procedure for radiofrequency (RF) ablation of hepatocellular carcinomas (HCCs) located on the liver surface as a possible alternative to RF ablation via laparoscopic approach or with the creation of artificial ascites.Materials and MethodsChanges in temperature of a sodium hyaluronate layer placed onto an egg white were measured during coagulation of the egg white by an RF ablation needle. A phase I study was performed to evaluate the safety of intraperitoneal injection of a maximum of 20 mL of sodium hyaluronate solution into humans by observing for the occurrence of intraperitoneal inflammation and adhesion. After these studies, RF ablation with ultrasound-guided injection of sodium hyaluronate onto the liver surface was performed, targeting 28 HCC nodules located on the liver surface. Treatment outcomes and complications of this procedure were investigated.ResultsIn the in vitro experiment, the maximum temperature of sodium hyaluronate solution was 41°C during RF ablation. No intraperitoneal inflammation or adhesions were observed after intraperitoneal injection of sodium hyaluronate in the phase I study. HCC was completely ablated with sufficient margins after one session of RF ablation, without any burn injuries to the abdominal wall or adjacent organs. Local recurrence was observed in one of 28 patients (3.6%) during 30.1 months of follow-up.ConclusionsRF ablation can be safely and effectively performed on HCCs located close to the liver surface with placement of sodium hyaluronate onto the liver surface, thereby preventing burn injuries to abdominal wall or adjacent organs.     

Percutaneous US-guided radiofrequency ablation with perfused needle applicators: improved survival with the VX2 tumor model in rabbits

PURPOSE: To evaluate survival, metastases, tumor necrosis, and prediction of local recurrence after percutaneous ultrasonographically (US) guided radiofrequency (RF) thermal ablation with electrodes perfused continuously with isotonic saline. MATERIALS AND METHODS: VX2 liver tumors were implanted in 31 rabbits according to a standardized protocol. After 21 days, 16 animals were treated percutaneously with RF ablation. Four animals died of complications related to anesthesia, and 12 animals were evaluated. All animals were followed for 110 days and monitored with computed tomography (CT) and US at 1, 7, and 30 days. A control group of 15 animals did not receive treatment. Autopsy was performed at the end of scheduled follow-up or immediately after death. For survival analysis, the Kaplan-Meier method was used; for nominal data, the Fisher exact test was used. RESULTS: In comparison to controls, animals in the treatment group showed significantly prolonged survival (P <.001). Eight of 12 animals (67%) treated with RF ablation survived to 110 days, while none of the controls did so. Metastases developed in all controls (100%) and in eight of 12 treated animals (67%) (P =.001). In comparison with controls, animals that developed metastases despite treatment also showed significantly prolonged survival (P =.02). Local recurrence was observed in three of 12 animals (25%) in the treatment group. CT and US performed 1 week after treatment did not allow prediction of local recurrence. CONCLUSION: RF ablation of liver tumors with perfused needle applicators prolongs survival in the VX2 rabbit liver tumor model, regardless of whether complete remission is achieved. In comparison with controls, RF ablation results in a lower frequency of metastases.     

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.     

Radiofrequency ablation for the treatment of liver tumors in the caudate lobe

PURPOSE: To evaluate the effectiveness of radiofrequency (RF) ablation for liver tumors located in the caudate lobe. MATERIALS AND METHODS: Ten patients (46-79 years of age; median, 70 y), eight with hepatocellular carcinoma (HCC) and cirrhosis and two with colorectal metastases in the caudate lobe, were treated with 5.8% NaCl tissue-perfused monopolar (n=7) or bipolar (n=3) RF ablation. The median tumor diameter was 41 mm (range, 25-70 mm). Procedures were performed under ultrasound and computed tomography (CT) guidance in eight and two patients, respectively. One month later, the treatment response was assessed by CT. RESULTS: Transhepatic right intercostal and transomental anterior epigastric routes were used for tumor puncture in eight and two patients, respectively. The entire RF ablation treatment required one or two procedures (median, 1.5), including two to 15 electrode repositionings (median, 6). After RF ablation procedure, one patient experienced jaundice that resolved spontaneously. In one patient, CT follow-up showed asymptomatic segmental biliary duct dilations. Median total hospital stay was 3 days (range, 2-9 d). Complete ablation was achieved in nine of 10 tumors. In one patient, ethanol ablation was necessary to complete RF ablation treatment. After a median follow up of 9.5 months (range, 5-25 mo), three patients remained tumor-free and seven had tumor relapse: two local, four distant, and one mixed. Repeat RF ablation was successfully performed in four cases. CONCLUSION: RF ablation of liver tumors located in the caudate lobe is effective despite the deep location of tumors and the vicinity of major vessels.     

Open radio-frequency thermal ablation of renal VX2 tumors in a rabbit model using a cooled-tip electrode: feasibility,safety, and effectiveness

The purpose of this study was to evaluate the feasibility, safety, and effectiveness of radio-frequency (RF) ablation using an internally cooled-tip electrode on renal VX2 tumors implanted in rabbits. Thirty-three rabbits with implanted renal VX2 tumors were divided into two groups: an RF ablation (RFA) group (n=27) and a control group (n=6). In the RFA group, RFA was performed on 27 implanted VX2 tumors using a cooled RF electrode and they were divided into three subgroups according to the follow-up period: acute (1–3 days, n=12); subacute (1–4 weeks, n=9); and chronic (2–7 months, n=6). Contrast-enhanced spiral CT was performed before the RFA and at the day, day 3, weeks 1, 2, 4, and months 2 and 7, after the RFA. The therapeutic efficacy was evaluated by the survival rate, CT, and pathologic findings. The RFA of renal tumors was technically successful in each instance. Complete tumor ablation was achieved in 22 of the 27 rabbits (81.5%) in the RFA group: 5 rabbits survived longer than 8 weeks without any evidence of viable tumor (18.5%) and 17 rabbits were found free of viable tumors when killed (63.0%). Five rabbits showed local tumor relapse and/or hematogenous lung metastasis after ablation (a recurrence rate of 18.5%). There were 11 (40.7%) complications related to the procedure. This experimental study demonstrates the feasibility of RFA therapy to treat renal VX2 tumors in rabbits, although RFA for central tumors carries some major potential complications, including renal arterial injury. Electronic Publication     

Evolving technology in bipolar perfused radiofrequency ablation: assessment of efficacy, predictability and safety in a pig liver model

Bipolar radiofrequency (RF) ablation, especially with perfusion of saline, has been shown to increase volume over monopolar conventional methods. The aims of this study are to study whether this method is linked to too flattened thermal lesions and premature rise of impedance and to elucidate some safety concerns. Eighteen RF ablations were performed using a 1.8-mm-diameter bipolar applicator in the liver of nine healthy pigs through laparotomy with or without temporary vascular occlusion [the Pringle maneuver (PGM)]: group A (n=9), without PGM; group B (n=9), with PGM. Hypertonic saline solutions (3% and 20 %) were injected through the applicator at a rate of 400 ml/h during the procedure. The pigs were followed up and they were euthanased on the 15th day. Impedance, current, power output, energy output, temperatures, diameters of thermal lesion, volume, sphericity ratio of thermal lesion were correlated among groups. Impedance at the end of the procedure (50.00 Ω±28.39 and 52.88 Ω±26.77, for groups A and B, respectively) was very similar to the starting impedance (50 Ω). In a median of 1 (range, 0–6) time per RF ablation procedure a reduction of 30 W from the selected power supply was observed during the RF ablation procedure linked to a slight increase of impedance. Volume and short diameter of thermal lesion were 21.28 cm³±11.78 and 2.85 cm±0.87 for group A, 87.51 cm³±25.20 and 4.31 cm±0.65 for group B. Continuous thermal between both electrodes were described with a global sphericity ratio of 1.91. One major complication (thermal injury to the stomach) was encountered in a case of cross-sectional necrosis of the targeted liver and attributed to heat diffusion after the procedure. This method has been shown to determine: (1) the relative control of impedance during the procedure; (2) ovoid and relatively large thermal lesions with less dependence upon closest vessels.This study was supported by a grant for medical research from Spanish Govern (FIS PI020317)