Radio-frequency thermal ablation with hypertonic saline solution injection of the lung: ex vivo and in vivo feasibility studies

The aim of this study was to assess the effects of simultaneous instillation of NaCl solutions during radio-frequency ablation (RFA) on the dimension of the ablated lesion in ex vivo bovine lung tissue and in vivo rabbit lung tissue. The RFA was induced in ex vivo bovine lung tissue which was inflated with room air and in vivo rabbit lung tissue by a 500-kHz RF generator and a 17-G cooled-tip electrode. In in vivo experiments, RFA was performed using CT guidance. The RF energy was applied for 5 min with or without instillation of 0.9 or 36% NaCl solutions. The changes in tissue impedance, current, power output, and temperature of the electrode tip were automatically measured. The maximum diameter of all thermal lesions was measured perpendicular to the electrode axis by two observers. In an ex vivo study, the mean lesion diameters using 36 and 0.9% NaCl solutions were larger than those of the control group: 51±8, 34±6, and 5±2 mm (p<0. 05). In in vivo rabbit lung tissue, the mean lesion diameter with NaCl solution (15.3±3.1 mm) was larger than that of the lesion without NaCl solution (8.5±1.4 mm; p<0.05). With instillation of NaCl solutions, a marked decrease of tissue impedance (>100 Ω) and corresponding increase of current flow occurred in both ex vivo and in vivo studies. This experimental study demonstrates that RF ablation with simultaneous NaCl solution infusion of the lung is more effective in achieving coagulation necrosis than conventional RFA procedure.     

Radio-frequency tissue ablation of the liver: effects of vascular occlusion on lesion diameter and biliary and portal damages in a pig model

The aim of this study was to assess the effect of vascular occlusion on radio-frequency (RF) lesion size and on potential associated biliary and portal lesions. Radio-frequency lesions using a 1-cm exposed-tip cooled electrode were created in pig liver. Liver perfusion was modified by arterial embolization (n=2), left portal clamping (n=2), and both (n=2). Two pigs were used as controls. Two weeks after, control portography was performed, animals were killed, and ex-vivo cholangiography was carried out. Pathological studies evaluated the lesion surface and associated portal and biliary damages. A mathematical regression model showed that portal occlusion increased by 43 mm2 (+40%) the surface of RF lesions, arterial occlusion by 135 mm2 (+126%), and associated occlusion by 466 mm2 (+435%). Biliary stenoses were found in 4 cases (two arterial occlusions, one portal occlusion, and one associated occlusion). One case of partial portal vein thrombosis was found in one case of portal occlusion and resolved at 2 weeks. Ischemic damages adjacent to RF lesions were found in cases of combined occlusions. The reduction of liver perfusion increases significantly the size of RF lesions but is associated with a risk of biliary, portal, or parenchymal complications.     

射频消融治疗化疗栓塞后肝癌

目的 评价射频消融治疗化疗栓塞后肝癌的临床疗效.方法 97例经病理证实的原发性肝癌患者在经过多次栓塞后仍有肿瘤残余,且均存在无法再栓塞的困难.所有患者均予CT导引下的肿瘤射频消融术.术后监测AFP的动态变化及肝脏CT或MRI的结果来评价疗效.结果 93例(96%)患者在12个月随访内无肿瘤复发征象,仅有4例患者出现了局灶复发和远处转移.结论 化疗栓塞术结合射频消融术是治疗肝癌的一种有效的联合治疗手段.     

Radio-frequency ablation of colorectal liver metastases in 167 patients

The objective of this paper is to report our results from a prospective study of 167 patients with colorectal liver metastases treated with radio-frequency ablation (RFA). Three hundred fifty-four treatments were performed in 167 patients, 99 males, mean age 57 years (34–87). The mean number of metastases was 4.1 (1–27). The mean maximum diameter was 3.9 cm (1–12). Fifty-one (31%) had stable/treated extra-hepatic disease. Treatments were performed under general anaesthesia using US and CT guidance and single or cluster water-cooled electrodes (Valleylab, Boulder, CO). All patients had been rejected for or had refused surgical resection. Eighty percent received chemotherapy. Survival data were stratified by tumour burden at the time of first RFA. The mean number of RFA treatments was 2.1 (1–7). During a mean follow-up of 17 months (0–89), 72 developed new liver metastases and 71 developed progressive extra-hepatic disease. There were 14/354 (4%) major local complications and 22/354 (6%) minor local complications. For patients with 5 metastases, maximum diameter 5 cm and no extra-hepatic disease, the 5-year survival from the time of diagnosis was 30% and from the time of first thermal ablation was 26%. Given that the 5-year survival for operable patients is a median of 32%, our 5-year survival of 30% is promising.     

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

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

An ex vivo study on radiofrequency tissue ablation: increased lesion size by using an "expandable-wet" electrode

The present comparative study was conducted to validate a newly developed "expandable-wet" electrode for an increased lesion size of radiofrequency ablation (RFA) on excised beef liver. The expandable-wet electrode, which allows interstitial hypertonic saline infusion through retractable curved needles, was compared with "expanded-dry" and "unexpanded-wet" electrodes for RFA lesion size and other parameters. A total of 120 lesions were created under 50 W (groups A-C) and 90 W (groups A'-C') power control mode for 10 min at each ablation site with the following groups: group A and A' of expanded-dry electrode (needles deployed but saline uninfused); group B and B' of unexpanded-wet electrode (saline infused but needle undeployed); and group C and C' of expanded-wet electrode (needles deployed and saline infused). Together with lower impedance and higher power output, the lesion size in group C (5.3+/-0.4 cm) and C' (6.0+/-1.0 cm) were significantly larger (P<0.01) than that in group A (3.3+/-0.3 cm) and A' (2.0+/-0.2 cm), and group B (3.8+/-1.0 cm) and B' (2.6+/-0.4 cm). The RFA lesion size can be significantly enlarged when the expandable electrode is complemented with interstitial hypertonic saline infusion. This design may improve the efficacy of RF tumor ablation.     

Internally cooled antenna for microwave ablation: results in ex vivo and in vivo porcine livers

PURPOSE: To evaluate the performance of microwave ablation with an internally cooled antenna in ex vivo and in vivo porcine livers. MATERIALS AND METHODS: Microwave ablations were performed in ex vivo and in vivo porcine livers with a 1.9 mm-diameter 2450 MHz microwave needle antenna. Four power settings (50, 60, 70 and 80 W) were used in this study, while application time was fixed at 10 min. Diameters of the coagulation zone were observed on gross specimens. RESULTS: Excessive elongation of coagulation along the needle shaft was not encountered in all ablations. An arrow-shaped charring was observed. As the power increases, the long-axis coagulation diameter for in vivo liver increased significantly (P<.05). The short-axis coagulation diameter for in vivo liver was significantly smaller than that for ex vivo liver (P<.05) but not statistically different among the four power settings. After 10 min of ablation at 80 W, the short-axis and long-axis coagulation diameter for in vivo liver was 4.92+/-0.15 cm and 2.37+/-0.10 cm, respectively. CONCLUSION: The internally cooled microwave antenna may be advantageous to minimize collateral damages.     

Radio-frequency thermal ablation of liver metastases with a cooled-tip electrode needle: results of a pilot clinical trial

The aim of this study was to evaluate feasibility, safety, and effectiveness of radio-frequency (RF) thermal ablation, performed by using a cooled-tip electrode needle, in the treatment of liver metastases. Twenty-nine patients (20 males and 9 females; age range 43–77 years) with one to four hepatic metastases 1.1–4.8 cm in diameter (mean 2.9 ± 0.8 cm) from previously resected intra-abdominal primary malignancies were treated. All patients were excluded from surgery and had partial or no response to chemotherapy. Radio-frequency ablation was performed by using a 100-W generator and 17-gauge, dual-lumen, cooled-tip electrode needles with a 2- to 3-cm exposed tip. Exposure time was 12 min for each needle insertion. Findings at spiral CT were used to assess the therapeutic response. A total of 127 insertions were performed (mean 2.4 ± 1.7 insertions/lesion) during 84 treatment sessions (mean 1.6 ± 0.7 sessions/lesion) in absence of major complications. Complete tumor response (i. e., unenhancing area of thermal necrosis larger than the treated tumor) was seen in 41 (77 %) of 53 lesions, including 33 (87 %) of 38 lesions 3 cm or less in diameter. After a mean follow-up period of 6.5 ± 2.1 months (range 3–9 months), recurrence of the treated lesion was seen in 5 (12 %) of the 41 cases. New metastatic lesions appeared in 7 patients. Two patients died after 6 and 8 months, respectively. Of the 27 patients still in follow-up, 14 are currently free of disease. Radio-frequency thermal ablation with a cooled-tip electrode needle is a safe and effective local treatment for hepatic metastases 3 cm or less in greatest dimension. Received: 5 September 1997: Revised: 8 January 1998: Accepted: 14 January 1998     

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.     

Multipolar radiofrequency ablation using 4-6 applicators simultaneously: a study in the ex vivo bovine liver

In this study the volume and shape of coagulation zones after multipolar radiofrequency ablation (RFA) with simultaneous use of 4-6 applicators in the ex vivo bovine liver were investigated. The RF-applicators were positioned in 13 different configurations to simulate ablation of large solitary tumors and simultaneous ablation of multiple lesions with 120 kJ of applied energy/session. In total, 110 coagulation zones were induced. Standardized measurements of the volume and shape of the coagulation zones were carried out on magnetic resonance images and statistically analyzed. The coagulation zones induced with solitary applicators and with 2 applicators were imperceptibly small and incomplete, respectively. At 20mm applicator distance, the total ablated volume was significantly larger if all applicators were arranged in a single group compared to placement in 2 distant applicator groups, each consisting of 3 applicators (p=.001). The mean total coagulated volume ranged from immeasurably small (if 6 solitary applicators were applied simultaneously) to 74.7 cc (if 6 applicators at 30 mm distance between neighboring applicators were combined to a single group). Applicator distance, number and positioning array impacted time and shape. The coagulation zones surrounding groups with 4-6 applicators were regularly shaped, homogeneous and completely fused, and the axial diameters were almost constant. In conclusion, multipolar RFA with 4-6 applicators is feasible. The multipolar simultaneous mode should be applied for large and solitary lesions only, small and multiple tumors should be ablated consecutively in standard multipolar mode with up to 3 applicators.     

Microwave ablation: Results with double 915 MHz antennae in ex vivo bovine Livers

Purpose

To investigate the settings for the optimal microwave ablation geometry with the simultaneous application of double 915 MHz antennae in ex vivo bovine livers, so as to provide the technical basis for treating large liver tumor in one ablation session.

Materials and methods

MWAs were performed on ex vivo bovine livers by simultaneously application of double 915 MHz internally cooled-shaft antennae. Four power settings (50, 60, 70 and 80 W) were used during MWAs, while application time was fixed at 10 min. Three inter-antenna distances (2.0, 2.5 and 3.0 cm) were used. Diameters and shapes of the coagulation zones were observed on gross specimens.

Results

(1) The coagulation shape was related to the inter-antenna distance, which was most spherical at an inter-antenna distance of 2.0 cm. A recess of the coagulation zone was observed at an inter-antenna distances of 2.5 and 3.0 cm. (2) The long-axis and short-axis coagulation diameter enlarged with increasing power output. However, there were no significant differences in the coagulation diameters between 70 and 80 W (P > 0.05). More desirable coagulation geometry could be obtained by simultaneous application of double antennae at 70 W for 10 min with an inter-antenna distance of 2.0 cm, the long-axis and short-axis coagulation diameter were 6.95 ± 0.32 cm and 5.30 ± 0.22 cm, respectively.

Conclusion

Simultaneous application of double 915 MHz antennae can generate large coagulation zones with desirable shape which may be advantageous for treating large liver tumor in one ablation session.     

Radiofrequency ablation of the porcine liver in vivo: increased coagulation with an internally cooled perfusion electrode

RATIONALE AND OBJECTIVES: A major limitation of radiofrequency (RF) ablation is its inability to produce a large enough diameter of coagulation necrosis to encompass hepatic tumors with an appropriate ablative margin at a single RF application. We evaluated the in vivo efficiency of RF ablation (RFA) using an internally cooled perfusion (ICP) electrode with hypertonic saline infusion to induce coagulation necrosis compared with that of RFA using single needle electrode types. MATERIALS AND METHODS: RF was applied to a porcine liver in monopolar mode using a 200 W generator and an internally cooled electrode (group A) or an ICP electrode (group B) at 200 W for 12 minutes or using a 60 W generator with a perfusion electrode at 40 W for 20 minutes (group C). In total, 36 (3 x 12) ablation zones were created using the three different regimens. In group B, 14.6% NaCl solution was infused at 1 mL/minute and in group C, 0.9% NaCl solution was infused at 1.5 mL/minute. The three groups were compared in terms of amount of delivered RF energy and dimensions and the coefficients of variation of the ablation zones. RESULTS: The mean energies applied in the three groups were 52.3 +/- 10.3 kJ for group A, 115.4 +/- 10.5 kJ for group B, and 38.5 +/- 11.5 kJ for group C, respectively (P < .05). The mean ablation volumes in groups A, B and C were 13.1 +/- 4.7 cm3 in group A, 43.7 +/- 17.5 cm3 in group B, and 26.3 +/- 20.2 cm3 in group C, respectively (P < .05). In addition, the coefficients of variation of the volumes of the ablation zones in groups A, B, and C were 0.36, 0.4, and 0.78, respectively. CONCLUSIONS: RFA using the ICP electrode showed better performance in terms of creating a larger ablation zone than RFA using an internally cooled or a perfusion electrode.     

The effect of radiofrequency ablation on different organs: Ex vivo and in vivo comparative studies

Objective

The purposes of this study are to evaluate the ex vivo and in vivo efficacy of radiofrequency ablation (RFA) on different porcine tissues by the ablation of three different sites simultaneously.

Materials and methods

A multichannel RFA system, enables three separate tumors to be ablated simultaneously, was used. RFA procedures were applied to normal porcine liver, kidney, and muscle together ex vivo (n = 12) and in vivo (n = 17). Pre-impedances, defined as baseline systemic impedances of tissues before beginning RFA, and the areas of ablation zones were measured and compared.

Results

The areas of ablation zones among three organs had a significant difference in decreasing order as follows: liver, muscle, and kidney in the ex vivo study (p = 0.001); muscle, liver, and kidney in the in vivo study (p < 0.0001). The areas of ablation zones between ex vivo and in vivo had a significant difference in the liver and muscle (each p < 0.05). There was no significant correlation between the areas of ablation zones and pre-impedances in both studies.

Conclusions

Renal RFA produced the smallest ablation zone in both in vivo and ex vivo studies. Muscular RFA demonstrated the largest ablation zone in the in vivo study, and hepatic RFA showed the largest ablation zone in the ex vivo study. This variability in the tissues should be considered for performing an optimized RFA for each organ site.     

Multipolar radiofrequency ablation using internally cooled electrodes in ex vivo bovine liver: correlation between volume of coagulation and amount of applied energy

Purpose

To evaluate the relationship between applied energy and volume of coagulation induced by multipolar radiofrequency (RF) ablation.

Methods and materials

Multipolar RF ablations (n = 80) were performed in ex vivo bovine liver. Three bipolar applicators with two electrodes located on each applicator shaft were placed in a triangular array. The power-output (75–225 W) and the distance between the different applicators (2, 3, 4, 5 cm) were systematically varied. The volume of confluent white coagulation and the amount of applied energy were assessed. Based on our experimental data the relationship between the volume of coagulation and applied energy was assessed by nonlinear regression analysis. The variability explained by the model was determined by the parameter r².

Results

The volume of coagulation increases with higher amounts of applied energy. The maximum amount of energy was applied at a power-output of 75 W and an applicator distance of 5 cm. The corresponding maximum volume of coagulation was 324 cm³ and required an application of 453 kJ. The relationship between amount of applied energy (E) and volume (V) of coagulation can be described by the function, V = 4.39E^0.7 (r² = 0.88). By approximation the volume of coagulation can be calculated by the linear function V = 0.61E + 40.7 (r² = 0.87).

Conclusion

Ex vivo the relationship between volume of coagulation and amount of applied energy can be described by mathematical modeling. The amount of applied energy correlates to the volume of coagulation and may be a useful parameter to monitor multipolar RF ablation.     

Quantitative magnetic resonance temperature mapping for real-time monitoring of radiofrequency ablation of the liver: an ex vivo study

We evaluated the feasibility and accuracy of real-time magnetic resonance (MR) thermometry for monitoring radiofrequency (RF) ablation in the liver. Continuous MR temperature mapping was used to monitor bipolar RF ablations performed in ex vivo livers with and without flow using two parallel electrodes. Macroscopic inspection of ablation zones was compared with thermal dose maps (TDm) and T1-weighted inversion recovery turbo spin echo (IR-TSE) images for their size and shape and the influence of flow. Pearson’s correlation (r), Bland and Altman tests and kappa (χK) tests were performed. The mean differences in ablation zone size between macroscopic and TDm and IR-TSE measurements were +4 mm and −2 mm, respectively. TDm was well correlated with macroscopy (r=0.77 versus r=0.44 for IR-TSE). TDm was found to be more precise for shape recognition (χK=0.73 versus χK=0.55 for IR-TSE) and for detection of an intact ring of liver due to the cooling effect of flow which was impossible with IR-TSE. Simultaneous monitoring of RF ablation by MR thermometry is feasible and reliable for predicting the shape of ablation zones and the impact of the heat-sink effect of flow. Further studies are needed to confirm these results in vivo.Electronic Supplementary Material Supplementary material is available for this article at Grant Support: Ligue National Contre le Cancer, French Ministry of Research and Philips Medical Systems.     

多弹头射频治疗肝癌36例报告

目的：探讨多弹头射频治疗肝癌的临床近期疗效。方法：对３６例肝癌患者进行射频治疗,通过对手术前后ＣＴ、Ｂ超检查的比较及ＡＦＰ、肝功能、机体免疫力、体重和自觉症状的改变进行对比观察。结果：３６例于治疗后７ｄ、１０例于治疗后３０ｄ经Ｂ超及ＣＴ检查;７ｄ后８０．６％的病人肿瘤体积缩小了３０％以上,３０ｄ后１０例病人肿瘤体积缩小了４０％以上,与术前相比瘤体内血供消失。８３．４％的病人自觉症状改善,ＡＦＰ值下降者占７７．８％,肝功能酶谱及胆红素均恢复正常,白蛋白平均增加１１．０ｇ．Ｌ＾－１。体重增加５．６ｋｇ,Ｔ淋巴细胞转化率平均增加２１％。ＩｇＧ平均增加２．０ｇ．Ｌ＾－１,无手术死亡。结论：多弹头射频治疗肝癌的适应证广、安全可靠、疗效满意。     

Percutaneous radiofrequency ablation: relationship between different probe types and procedure time on length and extent of osteonecrosis in dog long bones

Purpose We have been using radiofrequency ablation for the percutaneous treatment of osteoid osteoma since 2001. Frequently, lesions are located near the joint surface, involve the vertebral body or are close to major nerves. We seek to determine whether radiofrequency ablation (RFA) can be used safely in these cases. Materials and methods A total of 65 lesions were induced in 4 dogs. Each dog underwent RFA on the diaphysis of long bones, as well as femoral and humeral heads. Four different sessions were carried out by using 1- and 2-cm probes with or without a cool-tip system and by varying the timing of the procedure. Plain film, CT, and MRI were obtained. All bone samples were examined histologically. Results The dogs’ activity after the procedure was normal. No pathologic fractures occurred despite unrestricted activity of the animals. Cortical bone was always respected; therefore, articular cartilage has not been damaged. Radiological findings were characteristic. There were no significant differences in lesion size, probe type, and the duration of the procedure. The mean lesion diameter perpendicular to the electrode was 18.5 mm. Conclusions Our study confirms the insulative effect of cortical bone. RFA can be safely performed close to the joint surface without damaging the cartilage.     

Radiofrequency ablation of chondroblastoma: procedure technique,clinical and MR imaging follow up of four cases

Purpose  The aim of this study is to describe the procedure technique, clinical and imaging outcomes of patients treated with radiofrequency ablation for chondroblastoma. Materials and methods  Four patients (female/male, 3:1; mean age, 13 years; age range; 9–16 years) underwent the procedure. All had pre-operative magnetic resonance imaging (MRI) and symptomatic, biopsy-proven chondroblastomas (two proximal femur, two proximal tibia). The lesion size ranged from 1.5 to 2.5 cm in maximal dimension (mean size, 1.8 cm). Bone access was gained with a Bonopty biopsy needle system (mean number of radiofrequency needle placements, 5; mean ablation time, 31 min). Results  Clinical and MRI follow-up was available in all cases (mean, 12.25 months; range, 5–18 months). All patients reported resolution of symptoms at 2–6 weeks post ablation. At their most recent clinical follow-up, three patients remained completely asymptomatic with full return to normal activities and one patient had minor local discomfort (different pain pattern) that was not limiting activity. All four patients’ follow-up MRI studies demonstrated resolution of the oedema pattern around the lesion and temporal evolution of the internal signal characteristics with fatty replacement. Conclusion  Radiofrequency ablation for chondroblastoma provides an alternative to surgical curettage, and we have demonstrated both a clinical improvement in symptoms and the follow-up MRI appearances.     

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

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

Comparison of four radiofrequency ablation systems at two target volumes in an ex vivo bovine liver model

PURPOSE

We aimed to validate actually achieved macroscopic ablation volumes in relation to calculated target volumes using four different radiofrequency ablation (RFA) systems operated with default settings and protocols for 3 cm and 5 cm target volumes in ex vivo bovine liver.

MATERIALS AND METHODS

Sixty-four cuboid liver specimens were ablated with four commercially available RFA systems (Radionics Cool-tip, AngioDynamic 1500X, Boston Scientific RF 3000, Celon CelonPower LAB): 16 specimens for each system; eight for 3 cm, and eight for 5 cm. Ablation diameters were measured, volumes were calculated, and RFA times were recorded.

RESULTS

For the 3 cm target ablation volume, all tested RFA systems exceeded the mathematically calculated volume of 14.14 cm³. For the 3 cm target ablation volume, mean ablation volume and mean ablation time for each RFA system were as follows: 28.5±6.5 cm³, 12.0±0.0 min for Radionics Cool-tip; 17.1±4.9 cm³, 9.36±0.63 min for AngioDynamic 1500X; 29.7±11.7 cm³, 4.60±0.50 min for Boston Scientific RF 3000; and 28.8±7.0 cm³, 20.85±0.86 min for Celon Celon-Power LAB. For the 5 cm target ablation volume, Radionics Cool-tip (48.3±9.9 cm³, 12.0±0.0 min) and AngioDynamic 1500X (39.4±16.2 cm³, 19.59±1.13 min) did not reach the mathematically calculated target ablation volume (65.45 cm³), whereas Boston Scientific RF 3000 (71.8±14.5 cm³, 9.15±2.93 min) and Celon CelonPower LAB (93.9±28.1 cm³, 40.21±1.78 min) exceeded it.

CONCLUSION

While all systems reached the 3 cm target ablation volume, results were variable for the 5 cm target ablation volume. Only Boston Scientific RF 3000 and Celon CelonPower LAB created volumes above the target, whereas Radionics Cool-tip and AngioDynamic 1500X remained below the target volume. For the 3 cm target ablation volume, AngioDynamic 1500X with 21% deviation was closest to the target volume. For the 5 cm target volume Boston Scientific RF 3000 with 10% deviation was closest.Radiofrequency ablation (RFA) is a minimally invasive technique for eliminating both primary tumors and metastases. It may be particularly useful for treating patients with inoperable lesions or contraindications to open surgery. Since its introduction, percutaneous ablation has been established as an effective and safe treatment (1, 2), especially in patients with primary and secondary malignancies of the liver (3, 4), the kidney (5, 6), the lung (7, 8), and the breast (9, 10).As radiofrequency (RF) energy can only be deployed in a closed electrical circuit, monopolar RFA devices may require up to four neutral electrodes (grounding pads), commonly placed on the thighs. The large surface of the grounding pads (manufacturer-specific, up to 200 cm²) is intended to prevent excessive heating at the skin level; the surface of the active part(s) of the RF electrode(s) is about 100 times smaller (manufacturer-specific, usually 1–5 cm²) than the grounding pad surface area.Instead of monopolar systems with grounding pads, a different technique to apply RF energy is to use bipolar or multipolar devices (3, 11, 12). In bipolar devices, both the cathode and the anode are positioned within the active tip of the electrode, separated by an insulator. The current is applied between the electrodes; no grounding pads are needed. Multipolar systems induce synergetic heat effects by using a switching algorithm between two or more electrodes to induce synergetic heat effects (3).The volume and shape of the coagulation necrosis (due to possibly different diameter extensions in the three spatial dimensions) achievable with standard clinical RF generators (apart from the generators’ monopolar, bipolar or multipolar nature) depend especially on the impact of the energy applied, probe geometry, duration of heat exposure, fluid content of the target tissue, organ perfusion, and blood vessel density (13). Additionally, in in vivo settings, the so-called heat-sink effect has to be taken into account. The fluid content and perfusion of the tissue and blood vessel density in the target organ have been described as the main factors dissipating heat from the target site and thereby resulting in a smaller ablation volume (6).For hepatocellular carcinoma for example, based on commonly accepted patient selection criteria, only some patients are suited for conventional surgery, mainly because patients present with poor Child-Pugh status and/or metastases in both hepatic lobes at diagnosis. Delis and Dervenis (14) report that less than 30% of hepatocellular carcinoma patients are eligible for liver resection; thus, approximately 70% require different treatment approaches.RFA may be regarded as the most commonly used interventional modality in clinical practice, either for sole intervention or in combination with other methods, such as transarterial chemoembolization.In a patient, the actual volume of an induced RFA can usually not be dissected and assessed macroscopically after the procedure. Interventionalists have to rely on imaging to assess the ablation volume and geometry of the induced coagulation necrosis after ablation, and hence therapeutic success. With the different RFA systems available on the market, it is valuable to have a sound understanding of the systems’ behavior, especially in terms of ablation volume and geometry the specific RFA system creates, that one intends to clinically use.The objective of this study was to validate the measured size of actual ablation volumes in relation to mathematically calculated expected ablation volumes of four different RFA systems using default settings and protocols for 3 cm and 5 cm target ablation volumes in bovine ex vivo liver.