Radiofrequency renal ablation: in vivo comparison of internally cooled, multitined expandable and internally cooled perfusion electrodes

PURPOSE: To evaluate the in vivo efficiency of radiofrequency ablation using an internally cooled-perfusion (ICP) electrode for inducing coagulation necrosis compared with those of RFA using internally cooled or multitined expandable electrodes in porcine kidneys. MATERIALS AND METHODS: Using a 200 W generator and internally cooled and ICP electrodes or a 150 W generator and a multitined expandable electrode, a total of 15 radiofrequency ablations were performed in the kidneys of nine pigs. After placement of an electrode in the lower pole of a kidney, one ablation zone was created using one of three different regimens: group A, radiofrequency ablation using an internally cooled electrode; group B, radiofrequency ablation using an ICP electrode with 14.6% NaCl solution instillation at 1 mL/minute; group C, radiofrequency ablation using a multitined expandable electrode. Three days after the procedures, contrast-enhanced CT scans were obtained to evaluate ablation region volumes, and kidneys were harvested for gross measurements. The three groups were compared with respect to technical parameters such as changes in impedance and current during radiofrequency ablation. The dimensions of thermal ablation zones created in the three groups were compared histologically. RESULTS: In vivo study showed that ICP electrode allowed a greater energy delivery than internally cooled or multitined expandable electrode during radiofrequency ablation: 63.3 +/- 8.8 kJ in group A; 101 +/- 3.3 kJ in group B; and 61.8 +/- 12.5 kJ (P < .05). In vivo studies showed radiofrequency ablation using ICP electrode achieved larger mean coagulation volumes than radiofrequency ablation using the other electrodes: 12.0 +/- 3.9 cm(3) in group A; 30.5 +/- 7.6 cm(3) in group B; and 11.6 +/- 6.7 cm(3) in group C (P < .05). In addition, group B had a larger mean short-axis diameter of radiofrequency-induced coagulation necrosis than groups A or C: 2.6 +/- 0.5 cm in group A; 3.6 +/- 0.4 cm in group B; and 2.4 +/- 0.7 cm in group C (difference between groups B and C: P < .05). CONCLUSIONS: Radiofrequency ablation using an ICP electrode showed better performance at creating coagulation necrosis than radiofrequency ablation using internally cooled or multitined expandable electrodes in this porcine renal model.     

Percutaneous radiofrequency ablation of renal tumors: midterm results in 16 patients

PURPOSE: To evaluate the outcome of 16 patients after percutaneous radiofrequency ablation of renal tumors. MATERIALS AND METHODS: Sixteen patients (nine women, seven men; mean age, 61+/-9 years) with 24 unresectable renal tumors (mean volume, 4.3+/-4.3 cm3) underwent CT-guided (n=20) or MR imaging-guided (n=4) percutaneous radiofrequency ablation using an expandable electrode (Starburst XL, RITA Medical Systems, Mountain View, CA) with a 150-W generator. The initial follow-up imaging was performed within 1-30 days after RF ablation, then at 3-6 month intervals using either CT or MRI. Residual tumor volume and coagulation necrosis was assessed, and statistical correlation tests were obtained to determine the strength of the relationship between necrosis volume and number of ablations. RESULTS: Overall, 97 overlapping RF ablations were performed (mean, 3.5+/-1.5 ablations per tumor) during 24 sessions. Five or more RF ablations per tumor created significant larger necrosis volumes than 1-2 (p=.034) or 3-4 ablations (p=.020). A complete ablation was achieved in 20/24 tumors (primary technical success, 83%; mean volume of coagulation necrosis: 10.2+/-7.2 cm3). Three of four residual tumors were retreated and showed complete necrosis thereafter. Three major complications (one percuatneous urinary fistula and two ureteral strictures) were observed after RF ablation. No further clinically relevant complications were observed and renal function remained stable. During a mean follow-up of 11.2 months (range, 0.2-31.5), 15/16 patients (94%) were alive. Only one patient had evidence of local recurrent tumor. CONCLUSION: The midterm results of percutaneous RF ablation for renal tumors are promising and show that RF ablation is well-suited to preserve renal function.     

Percutaneous radiofrequency ablation of renal cell carcinoma: preliminary results

PURPOSE: To report early results in percutaneous radiofrequency ablation (RFA) of renal cell carcinoma with an expandable RF probe. MATERIAL AND METHODS: In 14 patients (9 male, mean age 67.9 +/- 9.9 years) CT-guided percutaneous radiofrequency ablation of 15 renal cell carcinomas was performed using an expandable LeVeen probe (diameter 2-4 cm) and a 200-watt generator under general anesthesia and CT control. Tumors exceeding a diameter of 3 cm (n=6) were embolized within 24 h prior to RFA. Average tumor size was 3.0 +/- 1.0 cm. RESULTS: RFA was technically successful in all patients, resulting in a mean size of necrosis of 3.7 +/- 0.7 cm. With the exception of one reno-cutaneous fistula, which was successfully treated conservatively, no major complications were observed. No local recurrence was observed (follow-up: 13.9 +/- 12.4 months) while extrarenal tumor progression occurred in four patients. CONCLUSION: Our preliminary data suggest that nephron sparing percutaneous RFA of renal tumors with an expandable RF probe is safe and effective.     

Comparison of renal ablation with monopolar radiofrequency and hypertonic-saline-augmented bipolar radiofrequency: in vitro and in vivo experimental studies

OBJECTIVE: We sought to determine whether hypertonic-saline (HS)-augmented bipolar radiofrequency ablation has advantages over monopolar radiofrequency ablation for creating larger areas of coagulation necrosis in the kidney. MATERIALS AND METHODS: Using a 200-W generator and bipolar perfused-cooled electrodes or a monopolar cooled-tip electrode, we performed 14 radiofrequency ablations in explanted bovine kidneys. Radiofrequency was applied in standard monopolar (n = 7) or bipolar (n = 7) modes at 100 W for 10 min. In the bipolar mode, the perfused-cooled electrodes were placed at interelectrode distances of 3 cm, and a 6% sodium chloride solution was instilled into tissue at a rate of 2 mL/min through the electrodes. For in vivo experiments, either monopolar (n = 7) or HS-augmented bipolar (n = 7) radiofrequency ablation was performed in the lower pole of canine kidneys. Three days after the procedure, contrast-enhanced CT scans were obtained to evaluate the volumes of the ablation regions, and the kidneys were harvested for gross measurements. Technical parameters such as changes in impedance and current during radiofrequency ablation and dimensions of the thermal ablation zones were compared between the two groups. RESULTS: In ex vivo and in vivo experiments, the frequency of the pulsed radiofrequency application caused by rises in impedance was higher in the monopolar mode than in the bipolar mode during the application of radiofrequency energy. The in vivo study showed that the bipolar radiofrequency ablation allowed larger mean current flows than the monopolar radiofrequency ablation (i.e., mean +/- SD, 1,654 +/- 144 mA vs 967 +/- 597 mA) (p < 0.05). Ex vivo studies revealed that the volumes of bipolar radiofrequency-induced ablation regions were substantially larger than those of monopolar radiofrequency-induced ablation regions (26.1 +/- 10.5 cm(3) vs 10.2 +/- 4.2 cm(3)). In vivo studies showed bipolar radiofrequency ablation achieved larger coagulation necrosis than monopolar radiofrequency (3.2 +/- 0.3 cm vs 2.4 +/-0.4 cm) (p < 0.05). This was confirmed by the measured volume of nonenhancing area on contrast-enhanced CT (20.4 +/- 6.4 cm(3) vs 13.5 +/- 6.0 cm(3)). CONCLUSION: HS-augmented bipolar radiofrequency ablation using perfused-cooled electrodes shows better performance in creating coagulation necrosis than monopolar radiofrequency ablation in the kidney of an animal model.     

Radiofrequency liver ablation: experimental comparative study of water-cooled versus expandable systems

OBJECTIVE. We evaluate the uniformity and reproducibility of thermal lesion ablation and quantify the volume of tissue destruction and hemorrhage induced with two different commercially available radiofrequency ablation devices. MATERIALS AND METHODS. A four-array anchor expandable needle electrode and a triple-cluster cooled-tip needle electrode were used to induce lesions in three explanted calf livers and in vivo in eight swine livers. The sizes of the radiofrequency-induced lesions were macroscopically evaluated by measuring two perpendicular dimensions immediately after the experiment. Bleeding was evaluated by weighing gauze swabs used to dry the hemorrhage caused by electrode insertions. RESULTS. In explanted liver, the mean diameter of the radiofrequency-induced lesion was 5.3 +/- 0.7 cm for the cooled-tip needle and 3.7 +/- 0.4 cm for the expandable needle (p = 0.042), which correspond to approximate volumes of 65.35 +/- 26.22 cm(3) and 26.67 +/- 9.59 cm(3), respectively (p < 0.002). In vivo, the mean diameter was 3.7 +/- 0.4 cm for the cooled-tip needle and 3 +/- 0.4 cm for the expandable needle (p < 0.0001), which correspond to approximate volumes of 24.18 +/- 7.56 cm(3) and 11.16 +/- 3.65 cm(3), respectively (p < 0.0001). Blood loss attained a median value of 3.5 g for the cooled-tip needle and 2.6 g for the expandable needle; this difference was not statistically significant (p = 0.06). CONCLUSION. The cooled-tip needle induced significantly larger lesions than the expandable needle, but the lesions produced by the expandable needle are more reproducible, uniform, and spheric. The larger size of the lesions produced by the cooled-tip needle may be attributed to the higher maximum power used by the generator and the higher energy deposition, which is due to the cooling of the needle electrode.     

Hepatic bipolar radiofrequency ablation using perfused-cooled electrodes: a comparative study in the ex vivo bovine liver

The purpose of this paper was to demonstrate the efficacy of the dual probe bipolar radiofrequency (RF) system with the perfused-cooled electrodes inducing coagulation necrosis in the ex vivo bovine liver. The perfused-cooled electrode that allows simultaneous internal cooling and interstitial hypertonic saline perfusion has been developed for RF ablation (RFA). RF was applied to excised bovine liver in a bipolar mode at 150 W using a 200 W generator with two perfused-cooled electrodes for 10 min. After placing the electrodes at 3 cm spacing in the explanted liver, 45 ablation zones were created with three different regimens: Group A, using both intraelectrode cooling and interstitial perfusion; group B, using only the intraelectrode cooling; and group C, using only interstitial perfusion. In groups A and C, RFA was performed with the infusion of 6% hypertonic saline at the rate of 2 ml min(-1). During RFA, we measured the tissue temperature at the midpoint between the two electrodes. The dimensions of the ablation zones and the changes in impedance, currents and liver temperature during RFA were compared in these three groups. The mean tissue impedance during RFA in group A (56.7+/-21.7 Omega) and group C (56.9+/-20.6 Omega) was significantly lower than group B (112+/-19.7 Omega) (p<0.001). The mean current was higher in group A (1765+/-128 mA) than groups B (760+/-321 mA) and C (1298+/-349 mA) (p<0.05). In addition, the shortest vertical diameter of coagulation necrosis was greater in groups A (4.9+/-0.5 cm) and C (4.6+/-0.7 cm) than in group B (3.5+/-0.4 cm) (p<0.05). The temperature at the mid-point between the two probes was higher in group A than other groups: 99 degrees C in group A, 88.9 degrees C in group B, and 94.3 degrees C in group C (p>0.05). The ratios of the diameter of the long-axis to the diameter of the vertical-axis of groups A, B and C were 1.1+/-0.1, 1.2+/-0.1, and 1.1+/-0.2, respectively (p<0.05). Bipolar RFA using intraelectrode cooling and the interstitial saline perfusion simultaneously produced ablation zones significantly larger than the area produced by only one measure.     

Wet radio-frequency ablation using multiple electrodes: comparative study of bipolar versus monopolar modes in the bovine liver

OBJECTIVE: To determine whether hypertonic saline (HS)-mediated bipolar radio-frequency (rf) application as advantages over monopolar simultaneous and alternating rf applications for creating larger areas of coagulation necrosis. MATERIALS AND METHODS: A total of 60 rf ablations using double perfused-cooled electrodes and a 200 W generator (CC-3 model, Radionics) were performed in three different modes in explanted bovine livers: simultaneous monopolar mode (groups A and A'); alternating monopolar mode (groups B and B'); or bipolar mode (groups C and C'). Electrodes were placed at inter-electrode distances of 3 and 5 cm, and HS (6% NaCl solution) was instilled into tissue at a rate of 1 mL/min through the electrodes. rf was applied for 10 (3 cm distance) or 15 min (5 cm distance). During rf application, we measured the tissue temperature at the mid-point between the two electrodes. Dimensions of the thermal ablation zones, and temperatures were compared between the 3 groups using analysis of variance or the Kruskal-Wallis test. To compare configurations of the ablation zones in each group, the ratio of longitudinal diameter (Dl) to vertical diameter (D(v)) was calculated. RESULTS: With a 3-cm inter-electrode spacing, the D(v) between the electrodes of ablated lesions was 2.4 +/- 1.2 cm in group A, 4.5 +/- 1.0 cm in group B, and 6.1 +/- 0.9 cm in group C (P < 0.05), and at a 5-cm spacing, groups B' and C' produced a single ablation area, but group A' produced two separated ablation spheres: the D(v)s were 1.4 +/- 0.2 in group A, 2.9 +/- 1.0 mm in group B, and 6.6 +/- 0.4 cm in group C (P < 0.05). For both 5- and 3-cm spacings, the temperatures at the mid-point were higher in bipolar mode than in either monopolar simultaneous or alternating modes. The ratios of Dl/D(v) of groups A, B, and C were 2.5 +/- 0.2, 1.4 +/- 0.1, and 1.1 +/- 0.1, respectively, and the corresponding figures of groups A', B' and C' were 4.5 +/- 0.2, 2.7 +/- 0.1, and 1.1 +/- 0.1, respectively (P < 0.05). CONCLUSION: HS-enhanced bipolar rf ablation creates larger, more regular coagulation necrosis than either monopolar simultaneous or alternating rf ablation.     

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.     

Radiofrequency ablation in pig lungs: in vivo comparison of internally cooled, perfusion and multitined expandable electrodes

The purpose of this study was to compare the amounts of in vivo coagulation obtained by radiofrequency (RF) ablation in porcine lung, using three types of electrodes. 15 in vivo ablation procedures were performed in the lungs of five pigs using three kinds of currently available RF devices under CT guidance. After placing an electrode in the lung, three ablation zones were created at each of three different regimens: Group A: RF ablation with an internally cooled electrode; Group B: RF ablation with a perfusion electrode, with instillation of 0.9% NaCl solution at a rate of 1.5 ml min(-1); Group C: RF ablation with a multitined expandable electrode. According to the manufacturer's recommendations, RF application times were 12 min in group A and 20 min in group B. In group C, RF energy was delivered for 7 min after a mean temperature of 110 degrees C was reached at 5 cm deployment. 36 min after the procedures, contrast-enhanced CT scans were obtained to evaluate the volume of zone of coagulation, and lungs were harvested for gross measurements. After macroscopic and histopathological analyses of 5 mm-thick lung sections, diameters, volumes and variation coefficients of regions of central coagulation were assessed. During RF ablation, the perfusion electrode allowed a larger energy delivery than the internally cooled or the multitined expandable electrodes, i.e. 33.6+/-4.7 kJ in group A, 40.0+/-8.2 kJ in group B and 23.5+/-6.1 kJ in group C (p<0.05). On gross observation, the cut surface of the gross specimen containing RF-induced coagulation showed that the ablated tissue appeared to be a central, firm, dark-brown area surrounded by an irregular outer margin (approximately 3-10 mm thick) of bright red tissue. In vivo studies showed that RF ablation using the perfusion electrode achieved larger coagulation volume than RF ablation using the other electrodes (p<0.05): 7.2+/-4.1 cm3 in group A; 16.9+/-5.5 cm3 in group B; 7.5+/-3.3 cm3 in group C. The corresponding variation coefficients were 0.55, 0.31, and 0.45, respectively. Our study shows that RF ablation using a perfusion electrode achieves a larger coagulation volume with an irregular margin than RF ablation using internally cooled or multitined expandable electrodes in the porcine lung.     

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.     

Radiofrequency ablation of hepatic tumors: increased tumor destruction with adjuvant liposomal doxorubicin therapy

OBJECTIVE: The purpose of this study was to determine whether the administration of liposomal doxorubicin before radiofrequency ablation increases coagulation more than radiofrequency alone in focal hepatic tumors. SUBJECTS AND METHODS: Fourteen focal hepatic tumors (diameter: mean +/- SD, 4.0+/-1.8 cm) in 10 patients (colorectal cancer, n = 3 patients; hepatocellular carcinoma, n = 4; neuroendocrine tumor, n = 2; breast cancer, n = 1) were treated with internally cooled radiofrequency ablation. In addition to undergoing radiofrequency, five patients (n = 7 lesions) were randomly assigned to receive 20 mg of IV doxorubicin in a long-circulating stealth liposome carrier (Doxil) 24 hr before ablation. Contrast-enhanced helical CT was performed immediately (within 30 min) after radiofrequency ablation (baseline) and 2-4 weeks after ablation. The volume of induced coagulation was measured by three-dimensional reconstruction techniques, and the measurements were compared. RESULTS: For tumors treated with radiofrequency alone, the volume of the thermal lesion had decreased 12-24% (mean +/- SD, 82.5% +/- 4.4% of initial volume) at 2-4 weeks after ablation. By comparison, increased tumor destruction at 2-4 weeks after ablation was observed for all lesions treated with combined Doxil and radiofrequency (p<0.001). Six lesions increased 24-36% in volume, and coagulation surrounding a small colorectal metastasis increased 342%. No coagulation was identified in four unablated control lesions in the two patients receiving Doxil alone. CONCLUSION: Our pilot clinical study suggests that adjuvant Doxil chemotherapy increases tumor destruction compared with radiofrequency ablation therapy alone in a variety of focal hepatic tumors. Optimization of this synergistic strategy may ultimately allow improved clinical efficacy and outcome.     

Radiofrequency ablation of normal lungs after pulmonary artery embolization with use of degradable starch microspheres: results in a porcine model

PURPOSE: The present study was performed to evaluate the effect of pulmonary artery embolization on radiofrequency (RF) ablation of normal porcine lungs. MATERIALS AND METHODS: RF ablation zones (n=34) were created in the normal lungs of five domestic pigs (five zones in each of the first two pigs and eight zones in each of the remaining three pigs) with an expandable multitined electrode with use of bilateral thoracotomy. RF ablation was performed without pulmonary artery embolization (group 1, n=8), immediately after embolization (group 2, n=11), 15 minutes after embolization (group 3, n=7), and 30 minutes after embolization (group 4, n=8) with degradable starch microspheres. Among them, 12 ablation zones were excluded from this study because they were considerably limited by the presence of the pleura or large bronchi. The remaining 22 zones were included (n=7, n=5, n=4, and n=6 in groups 1, 2, 3, and 4, respectively). Coagulation necrosis volumes in the ablation zones were measured and compared among the groups. RESULTS: Coagulation necrosis volumes were 0.9+/-0.5 cm3, 2.1+/-0.4 cm3, 2.1+/-1.0 cm3, and 1.9+/-0.6 cm3 in groups 1, 2, 3, and 4, respectively. Groups 2-4 showed significantly larger coagulation volumes than group 1 (P=.012, P=.023, and P=.010 in groups 2, 3, and 4, respectively). CONCLUSION: Pulmonary artery embolization contributed to larger volumes of coagulation necrosis after RF ablation of normal lungs.     

Radiofrequency ablation of hepatic tumors: variability of lesion size using a single ablation device

OBJECTIVE: In this study, we examined the variability of lesion sizes produced by a single radiofrequency ablation using the same device and algorithm in patients with small malignant hepatic tumors. MATERIALS AND METHODS: A review of the clinical records of 208 patients who underwent radiofrequency ablation of malignant hepatic tumors during a 6-year period revealed 31 patients with small tumors that were treated with a single ablation. Clinical data were recorded using standardized work sheets. Tumor and lesion sizes after ablation were measured from CT scans. The influences of tumor size, tumor type, presence or absence of cirrhosis, and tissue temperature on the ablation size were analyzed. RESULTS: The size of tumor before treatment ranged from 0.8 to 4.0 cm (mean diameter [+/- SD] = 1.8 +/- 0.9 cm) with corresponding volumes of 0.27-30.24 mL (mean volume = 27.1 +/- 15.9 mL). The lesion sizes after ablation ranged from 1.7 to 5.3 cm (mean diameter = 3.6 +/- 0.7 cm) with corresponding volumes of 2.29-75.87 mL (mean volume = 4.9 +/- 7.1 mL). Tumor type (p > 0.25), presence or absence of cirrhosis (p > 0.45), and tissue temperature (p = 0.055) had no relationship to ablation size. Tumor size had a statistically significant influence on ablation lesion size (p < 0.04). Ablation of small tumors (diameter < or = 2.25 cm, n = 32) produced random lesion sizes whereas ablation of large tumors (diameter > 2.25 cm, n = 11) produced larger lesions (mean diameter = 4.0 +/- 0.8 cm). CONCLUSION: Significant variation occurs in the lesion size produced using the same ablation device and algorithm. These findings must be considered when planning ablation strategies.     

Combined radiofrequency and alcohol injection for percutaneous hepatic tumor ablation

OBJECTIVE: We sought to determine if alcohol potentiates radiofrequency energy by obtaining larger ablative volumes in 30 liver tumors in human patients. SUBJECTS AND METHODS: We compared two groups of patients: one group treated with radiofrequency ablation alone (radiofrequency-alone group), and a second group treated with radiofrequency ablation and immediate prior injection of alcohol (combined group). The radiofrequency-alone group comprised 20 ablations (mean diameter, 8.4 cm; colorectal cancer metastases [n = 15]; other metastases [n = 5]). The combined group consisted of 30 radiofrequency ablations (mean diameter, 8.8 cm; metastatic colorectal cancer [n = 17]; other metastases [n = 8]; and hepatocellular carcinoma [n = 5]) treated with alcohol injection immediately before radiofrequency ablation. The amount of alcohol injected was determined by the size and location of tumors. Preprocedural laboratory tests (complete blood cell count with differential, liver function tests, and coagulation parameters) were performed in all patients, along with pre- and postprocedural CT, MRI, and PET. Measurements of tissue necrosis were obtained on the postprocedural CT scans and MR images. Volumes of necrosis calculated in each group were corrected for the number of radiofrequency applications and were statistically compared using the Student's t test. In addition, tissue impedances obtained during the radiofrequency ablation procedure were compared between the two groups. RESULTS: The mean ablation volumes for the radiofrequency-alone group were 32.3 cm(2) (median, 28.6 cm(2); range, 14.4-61.8 cm(2)) and for the combined group, 84.6 cm(2) (median, 78.3 cm(2); range, 34.6-149 cm(2)). The difference in the necrosis volumes was significantly larger (p < 0.0001) in the combined group. Overall, the combined treatment group underwent fewer radiofrequency applications per session. Tissue impedance during radiofrequency ablation was higher in the combined group (mean, 62.7 vs 57.3 Omega in the radiofrequency alone group; p = 0.0005) at comparable times during the ablations. No major complications were seen in either group. CONCLUSION: Percutaneous radiofrequency ablation appears to be potentiated by immediate prior alcohol injection into the tumor. Consistently larger lesions are obtainable in fewer sessions, without any increase of complications, using the combined method.     

In vivo efficiency of multipolar radiofrequency ablation with two bipolar electrodes: a comparative experimental study in pig kidney

PURPOSE: To compare in vivo efficacy of multipolar radiofrequency (RF) ablation with two internally cooled electrodes to that of monopolar RF ablation with internally cooled single and cluster needles to induce coagulation in in vivo porcine kidneys. MATERIALS AND METHODS: Twenty-four coagulations were created in the kidneys of 12 pigs by means of laparotomy by using a monopolar or multipolar RF system. In the monopolar mode, RF was applied to a single internally cooled probe (group A) or to a cluster probe (group B) for 12 minutes. In the multipolar mode, RF was applied to two bipolar probes with 2-cm interprobe spacing up to 50 kJ (group C). Technical parameters and the dimensions, shapes, and coefficients of variation of the coagulations were compared among the three groups. RESULTS: The minimum transverse diameters of the RF-induced coagulations in groups B (3.5 cm+/-0.5) and C (3.8 cm+/-0.6) were significantly larger than that in group A (2.6 cm+/-0.3). The mean coagulation volumes produced in the multipolar group (25.1 cm3+/-5.2) were greater than those produced in the monopolar groups (11.6 cm3+/-3.7 and 18.1 cm3+/-5.8) (P<.05). The mean ratio of transverse diameter to vertical diameter of the coagulations was larger in groups B and C (1.2+/-0.2 and 1.0+/-0.1, respectively) than in group A (0.8+/-0.2) (P<.05). In addition, the coefficients of variation for groups A, B, and C were 0.33, 0.30, and 0.21, respectively. The procedure time was longer with the multipolar technique (27.2 minutes+/-4.9) than with the monopolar technique with a single or cluster probe (12 minutes). CONCLUSIONS: Multipolar RF ablation showed at least equivalent or better in vivo efficiency for creating a larger coagulation than monopolar RF ablation with single or cluster electrodes, but with a longer procedure time and at slightly greater complexity.     

Percutaneous saline-enhanced radiofrequency ablation of unresectable hepatic tumors: initial experience in 26 patients

OBJECTIVE: The purpose of our study was to evaluate the safety and efficacy of percutaneous saline-enhanced radiofrequency ablation for unresectable primary or metastatic hepatic tumors. SUBJECTS AND METHODS: Twenty-six patients with 15 hepatocellular carcinomas and 33 hepatic metastases (maximum diameter < or = 8.6 cm) were treated; of these, seven tumors in five patients were treated twice. Thus, 44 radiofrequency treatments were performed. Saline-enhanced and impedance-controlled radiofrequency ablation (0.5-1.1 mL/min of saline, 15-mm conductive portion of the electrode tip, 25-60 W, 5-43 min) was performed using MR imaging guidance. Coagulation necrosis, volume indexes, morbidity, and complications were assessed. RESULTS: The volume of coagulation necrosis 1-7 days after radiofrequency ablation was 1.6-126.6 cm(3) (median, 18.9 cm(3)), corresponding to coagulation diameters of 1.5-6.2 cm (median, 3.2 cm). The coagulation volume was significantly larger if there were more than four radiofrequency applications (p = 0.006). Tumors of 3 cm or less in diameter were eight times as likely to be successfully completely ablated (p = 0.01) and volume indexes of lesions treated with the patient under general anesthesia were significantly larger than those treated with the patient under conscious sedation (p < 0.001). Major complications occurred in four patients (15%). Incomplete ablation in 19 (35%) of 54 radiofrequency lesions was due to cooling by a large vessel nearby (n = 2) or to low power applied in painful (n = 11) or critical (n = 6) locations. Residual tumor was observed in 14 (58%) of 24 tumors evaluated 6-8 months after radiofrequency ablation. CONCLUSION: Percutaneous saline-enhanced and impedance-controlled radiofrequency ablation can be effective in the treatment of unresectable hepatic tumors and minimizes potential carbonization. A greater number of radiofrequency applications, general anesthesia, and increasing experience provide significantly better results.     

Multiple-electrode radiofrequency ablation: simultaneous production of separate zones of coagulation in an in vivo porcine liver model

PURPOSE: A multiple-electrode radiofrequency (RF) system was developed based on switching between electrodes that allows for the simultaneous use of as many as three electrically independent electrodes. The purpose of this study was to determine if each multiple-electrode ablation zone is identical to an ablation zone created with conventional single-electrode mode. MATERIALS AND METHODS: Nine female domestic pigs (mean weight, 90 kg) were used for this study. A prototype monopolar multiple-electrode RF ablation system was created with use of an RF generator and an electronic switching algorithm. A maximum of three electrodes can be used simultaneously by switching between electrodes at each impedance spike (30 omega greater than baseline levels). A total of 39 zones of ablation were created at open laparotomy in pig livers with use of a conventional single electrode (n = 9), two single electrodes simultaneously (n = 6 ablations; 12 ablation zones), or three single electrodes simultaneously (n = 6 ablations; 18 ablation zones). RF electrodes were spaced in separate lobes of the liver when multiple zones of coagulation were created simultaneously. Animals were euthanized after RF ablation, livers were removed, and ablation zones were sectioned and measured. RESULTS: Zones of coagulation created simultaneously with two or three electrodes were equivalent to ablation zones created with use of conventional single-electrode ablation. No significant differences were observed among control animals treated with a single electrode, those with two separate zones of ablation created simultaneously, and those with three simultaneously created ablation zones in terms of mean (+/-SD) minimum diameter (1.6 cm +/- 0.6, 1.6 cm +/- 0.5, and 1.7 cm +/- 0.4, respectively), maximum diameter (2.0 cm +/- 0.5, 2.3 cm +/- 0.5, 2.2 cm +/- 0.5, respectively), and volume (6.7 cm3 +/- 3.7, 7.4 cm3 +/- 3.8, and 7.8 cm3 +/- 3.9; P > .30, analysis of variance, pairwise t-test comparisons). CONCLUSIONS: A rapid-switching multiple-electrode RF system was able to simultaneously create as many as three separate ablation zones of equivalent size compared with single-electrode controls. This system would allow physicians to simultaneously treat multiple tumors, substantially reducing procedure time and anesthesia risk.     

Multiple probe radiofrequency ablation: pilot study in an animal model

PURPOSE: Radiofrequency ablation (RFA) is becoming increasingly popular for the minimally invasive treatment of benign and malignant tumors. Currently available systems are limited to the use of a single probe because of electrical interactions between probes. The purpose of this study was to test a new prototype multiple probe generator with a built-in switching mechanism to determine if multiple zones of necrosis could be formed simultaneously without a significant penalty in terms of lesion size and procedure time. MATERIALS AND METHODS: A dual probe generator was created by modifying a commercially available system into an alternating monopolar system with an external electronic switch controlled by a temperature feedback loop. A total of 20 radiofrequency (RF) lesions (conventional single probe, n = 10; switched dual probe, n = 10) were created in the livers of six adult pigs (temperature, 100 degrees C; 10-minute ablation). Lesions were excised and examined for volume, minimum diameter, and maximum diameter. RESULTS: The time to target temperature was slightly greater for dual (3.5 minutes) versus single ablations (2.7 minutes). However, this resulted in only a 48 second (6.5%) longer total ablation time. There was no significant difference between conventional single and dual lesions for lesion volume (13.6 +/- 9.3 cm(3) versus 13.7 +/- 7.0 cm(3); P >.05), minimum diameter (1.63 +/- 0.56 cm(3) versus 1.61 +/- 0.53; P >.05) or maximum diameter (3.3 +/- 0.84 versus 3.4 +/- 0.55, P >.05). CONCLUSION: A multiple probe RFA system that can simultaneously ablate multiple areas in the liver is feasible. If multiple probe units become clinically available, large or irregularly shaped lesions could be treated more effectively than with conventional single probe units, and multiple tumors could be ablated simultaneously, thus potentially decreasing procedure time and anesthetic complications.     

Sonographically observed echogenic response during intraoperative radiofrequency ablation of cirrhotic livers: pathologic correlation

OBJECTIVE: We performed a study to determine the correlation between the diameter of the echogenic response observed with intraoperative sonography during radiofrequency ablation of the cirrhotic liver and the mean diameter of tissue necrosis. SUBJECTS AND METHODS: A total of 22 intraoperative radiofrequency ablations were created in 11 cirrhotic livers. The largest diameter of the sonographically observed echogenic response surrounding and perpendicular to the radiofrequency probe was measured. The subsequent zone of necrosis observed at pathology in the hepatectomy specimens after liver transplantation was measured in three planes and compared with the measured diameter of the echogenic response. RESULTS: During all except three ablations, a hyperechoic region was visualized surrounding the radiofrequency probe. The diameter of the echogenic response correlated significantly with the mean diameter of necrosis (correlation coefficient, 0.84). However, the echogenic response overestimated the minimal diameter of necrosis (mean difference, 0.8 +/- 0.4 cm) in 18 of 22 ablations and underestimated the maximum diameter of necrosis (mean difference, 0.9 +/- 0.8 cm) in 16 of 22 ablations. CONCLUSION: The diameter of the echogenic response observed with intraoperative sonography during radiofrequency ablation of the cirrhotic liver correlates closely with the mean diameter of the subsequent area of tissue necrosis. However, the solitary diameter of the echogenic response as measured in our study was often greater than the smallest diameter and less than the largest diameter of the area of tissue necrosis. Therefore, the echogenic response associated with radiofrequency ablation of the cirrhotic liver should be viewed only as a rough approximation of the area of induced tissue necrosis; the final assessment of the adequacy of ablation should be deferred to an alternative imaging technique.     

Radiofrequency ablation for hepatocellular carcinoma: a prospective comparison of four radiofrequency devices

PURPOSE: To compare the effectiveness of ablation techniques for hepatocellular carcinoma (HCC) with the use of four radiofrequency (RF) devices. MATERIALS AND METHODS: One hundred patients with 133 HCC lesions no larger than 4 cm were treated with one of four RF devices: RF 2000 (maximum power, 100 W) and RF 3000 generators (maximum power, 200 W) with LeVeen expandable electrodes with a maximum dimension of 3.5 cm or 4 cm, internally cooled single electrode with a thermal dimension of 3 cm, and a RITA RF generator with expandable electrodes with a maximum dimension of 5 cm. RESULTS: Numbers of RF sessions needed per HCC to achieve complete necrosis were 1.4 +/- 0.5 with the RF 2000 device and greater than 1.1 +/- 0.3 with the other three devices (P < .05). The RF 2000 device required a more interactive algorithm than the RF 3000 device. Session times per patient were 31.7 minutes +/- 13.2 in the RF 2000 group and longer than 16.6 minutes +/- 7.5 in the RF 3000 group, 28.3 minutes +/- 12 in the RITA device group, and 27.1 minutes +/- 12 with the internally cooled electrode device (P < .005 for RF 2000 vs other devices and for RF 3000 vs RITA or internally cooled electrode device). Complete necrosis and local tumor progression rates at 2 years in the RF 2000, RF 3000, RITA, and internally cooled electrode device groups were 91.1%, 97.1%, 96.7%, and 96.8% and 12%, 8%, 8.2%, and 8.3%, respectively (P = .37). CONCLUSIONS: Ablation with the RF 3000 device required a shorter time than the other three devices and required a less interactive algorithm than the RF 2000 device. However, complete necrosis and local tumor progression rates were similar among devices.