Dual-probe radiofrequency ablation: an in vitro experimental study in bovine liver

OBJECTIVE: To determine whether alternative radiofrequency (RF) application with dual probes has advantages over sequential or simultaneous RF application for creating larger coagulation necrosis. MATERIALS AND METHODS: Using 2 17-gauge internally cooled electrodes and a 200-watt generator (CC-3 model, Radionics), RF energy was applied sequentially (group A, n = 20), simultaneously (group B, n = 20), or alternately (group C, n = 20) to explanted bovine liver. After preliminary experiments with a probe distance of 2-5 cm, a distance of 2 cm and 3 cm were chosen for main experiments. Total duration of the RF application was 10 minutes. In the alternative mode, the energy was applied alternately to both RF electrodes in 2-second intervals. Changes occurring in tissue impedance, current, power output, and temperature at the midpoint between the 2 electrodes were measured. The technical parameters, temperatures, and dimension of the ablated area were compared in the 3 groups using analysis of variance or Kruskal-Wallis test. RESULTS: In the groups B and C, the impedance was gradually decreased during RF application and the mean current flow of both groups was 1550 +/- 130 mA and 1375 +/- 175 mA, respectively. However, in the group A, the impedance was markedly increased during RF application, and the mean current was 940 +/- 484 mA (P < 0.05, between groups A and B, and groups A and C). With 3-cm spacing, the alternative RF application created oval-shaped ablation zones with larger shortest axis diameter at the midpoint than either the sequential or simultaneous RF application: 12.0 +/- 7.1 mm in group A; 27.0 +/- 3.1 mm in group B; 34.9 +/- 3.4 mm in group C (P < 0.05). With 2 cm spacing, the corresponding figures were 25.3 +/- 7.8 mm in group A; 34.9 +/- 7.8 mm in group B; 41.5 +/- 1.8 mm in group C (P < 0.05): the differences between groups A and B, and between groups A and C were statistically significant (P < 0.05). With 3-cm spacing, the temperature at the midpoint between the 2 probes was higher in group C (102 degrees C) than in either the group A (62 degrees C) or the group B (78 degrees C; P < 0.05). With 2-cm spacing, groups B and C showed higher temperature than group A (P < 0.05), but the difference between groups B and C was not significant (P > 0.05). CONCLUSION: The alternative RF application creates larger, more regular ablation zones than either the sequential or simultaneous RF application. This result suggests that use of an alternating RF power application will improve the results of RF ablation for the treatment of larger tumors.     

Bipolar radiofrequency ablation using internally cooled electrodes in ex vivo bovine liver: prediction of coagulation volume from applied energy

OBJECTIVE: We sought to evaluate the relationship between parameters of bipolar radiofrequency (RF) ablation using internally cooled electrodes. MATERIALS AND METHODS: Bipolar RF ablations (n = 24) were performed in ex vivo bovine liver using an internally cooled applicator with 2 electrodes located on the same shaft. The power-output was systematically varied (20-75 W). On the basis of our experimental data, mathematical functions were fitted and the goodness-of-fit was assessed by the parameter R. RESULTS: The duration to induce an increase of tissue resistance and the amount of applied energy increased with a decreased power-output. The maximum short-axis was 4.5 cm (20 W) and required an application of 64 kilojoules (kJ). The volume of coagulation can be determined as a function of the duration of energy application (R = 0.954) and the amount of applied energy (R = 0.945). CONCLUSION: The amount of applied energy and the duration of energy application can predict the volume of induced coagulation and may be useful to control internally cooled bipolar RF ablation.     

Multipolar radiofrequency ablation with internally cooled electrodes: experimental study in ex vivo bovine liver with mathematic modeling

PURPOSE: To evaluate the size and geometry of thermally induced coagulation by using multipolar radiofrequency (RF) ablation and to determine a mathematic model to predict coagulation volume. MATERIALS AND METHODS: Multipolar RF ablations (n = 80) were performed in ex vivo bovine livers by using three internally cooled bipolar applicators with two electrodes on the same shaft. Applicators were placed in a triangular array (spacing, 2-5 cm) and were activated in multipolar mode (power output, 75-225 W). The size and geometry of the coagulation zone, together with ablation time, were assessed. Mathematic functions were fitted, and the goodness of fit was assessed by using r(2). RESULTS: Coagulation volume, short-axis diameter, and ablation time were dependent on power output and applicator distance. The maximum zone of coagulation (volume, 324 cm(3); short-axis diameter, 8.4 cm; ablation time, 193 min) was induced with a power output of 75 W at an applicator distance of 5 cm. Coagulation volume and ablation time decreased as power output increased. Power outputs of 100-125 W at applicator distances of 2-4 cm led to a reasonable compromise between coagulation volume and ablation time. At 2 cm (100 W), coagulation volume, short-axis diameter, and ablation time were 66 cm(3), 4.5 cm, and 19 min, respectively; at 3 cm (100 W), 90 cm(3), 5.2 cm, and 22 min, respectively; at 4 cm (100 W), 132 cm(3), 6.1 cm, and 27 min, respectively; at 2 cm (125 W), 56 cm(3), 4.2 cm, and 9 min, respectively; at 3 cm (125 W), 73 cm(3), 4.9 cm, and 12 min, respectively; and at 4 cm (125 W), 103 cm(3), 5.5 cm, and 16 min, respectively. At applicator distances of 4 cm (>125 W) and 5 cm (>100 W), the zones of coagulation were not confluent. Coagulation volume (r(2) = 0.80) and RF ablation time (r(2) = 0.93) were determined by using the mathematic model. CONCLUSION: Multipolar RF ablation with three bipolar applicators may produce large volumes of confluent coagulation ex vivo. A compromise is necessary between prolonged RF ablations at lower power outputs, which produce larger volumes of coagulation, and faster RF ablations at higher power outputs, which produce smaller volumes of coagulation.     

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.     

An ex-vivo experimental study on optimization of bipolar radiofrequency liver ablation using perfusion-cooled electrodes

PURPOSE: To determine optimal parameters for bipolar radiofrequency ablation (RFA) using perfusion-cooled electrodes to create a large ablation volume in ex vivo bovine liver. MATERIAL AND METHODS: Three sets of RF experiments were performed using a 200-Watt generator and two 15-gauge perfusion-cooled or internally cooled electrodes in ex vivo bovine livers. In the first set of experiments, to find the ideal inter-electrode distance for creating large coagulation necrosis, 30 ablation lesions were created by bipolar RFAs at inter-electrode spacings of 3 cm, 4 cm, and 5 cm. In the second set of experiments, to explore the ideal duration of RF application, bipolar RFAs were performed for 10 min and 20 min. In the first and second experiments, 10 lesions were made for each condition with infusion of 6% hypertonic saline (HS) at 2 ml/min. In the third set of experiments, 10 ablation lesions were created by bipolar RFAs using internally cooled electrodes without HS infusion. The mean volume of those ablation lesions was then compared to that of the lesions created by bipolar RFA using perfusion-cooled electrodes in the second experiments. Tissue impedance, dimension, and shape of the ablated areas were compared in each condition. RESULTS: In the first set of experiments, bipolar RFA created a homogeneous oval or spherical-shaped ablation area between the electrodes at 3-5 cm spacing, but showed a more spherical-shaped lesion at 3 cm inter-electrode spacing than at 4 cm and 5 cm spacing. In the second set of experiments, RF energy delivered for 20 min created a larger dimension of coagulation necrosis than energy delivered for 10 min: 107.6 +/- 34 cm3 versus 59.5 +/- 27 cm3 (P<0.05). In addition, the mean volume of ablation regions obtained with bipolar RFA using the internally cooled electrode was 47.5+/- 17 cm3, which was significantly less than that with bipolar RFA using perfusion-cooled electrodes (P <0.05). CONCLUSION: Bipolar RFA using perfusion-cooled electrodes achieves homogeneous areas of coagulation necrosis between two electrodes, preferably at 3 or 4 cm inter-electrode distance for 20 min, and is better in creating large coagulation necrosis than bipolar RFA using internally cooled electrodes.     

Bipolar saline-enhanced electrode for radiofrequency ablation: results of experimental study of in vivo porcine liver

PURPOSE: To evaluate whether a bipolar saline-enhanced radiofrequency (RF) ablation system embedded in one needle is able to consistently produce homogeneous and predictable areas of coagulation necrosis with or without the Pringle maneuver of vascular inflow occlusion. MATERIALS AND METHODS: RF ablation (480 kHz) of the liver was performed in 24 healthy pigs by means of laparotomy: group A (n = 5), 4-cm distance between electrodes 1 and 2; group B (n = 7), 4-cm distance and the Pringle maneuver; group C (n = 5), 2-cm distance; and group D (n = 7), 2-cm distance with the Pringle maneuver. Twenty percent NaCl solution was infused continuously at a rate of 100 mL/h via each electrode during the procedure. The pigs were followed up, and they were euthanized on the 7th day. Livers were removed for histologic assessment. Time, impedance, current, power output, specific voltage of the contacts, energy output, temperatures in the liver, volume of the lesion, and energy delivered per lesion volume were determined and compared among groups. Predictability of lesion volume was evaluated with the coefficient of variability. Mean values of the variables were compared among the groups by means of one-way analysis of variance or Kruskall-Wallis test. RESULTS: Impedance at the end of the RF ablation procedure was almost twofold lower than the corresponding initial value in all groups. In Pringle groups B and D, regular ellipsoids of coagulation necrosis were created (mean lesion volume, 149.50 cm3 +/- 34.26 and 69.43 cm3 +/- 15.48, respectively). In non-Pringle groups A and C, the shape of coagulation necrosis was influenced by the vessels encountered, and mean lesion size was lower than that in the Pringle groups (P <.01). The coefficient of variability of lesion size was lower in the Pringle groups (23% and 22%, respectively) than that in the non-Pringle groups (75% and 30%, respectively). CONCLUSION: The bipolar saline-enhanced RF ablation method produces homogeneous and predictable areas of coagulation necrosis between two electrodes, regardless of the distance between them, preferably with vascular inflow occlusion.     

Targeting liver lesions for radiofrequency ablation: an experimental feasibility study using a CT-US fusion imaging system

PURPOSE: To investigate the feasibility and validity of real-time guidance using a fusion imaging system that combines ultrasound (US) and computed tomography (CT) in the targeting and subsequent radiofrequency (RF) ablation of a liver target inconspicuous on US. METHODS AND MATERIALS: The study was designed as an experimental ex vivo study in calf livers with radiopaque internal targets, inconspicuous at US, simulating a focal liver lesion. The study included 2 phases. The initial phase was to examine the feasibility of matching preprocedural volumetric CT data of the calf livers with real-time US using a commercially available multimodality fusion imaging system (Virtual Navigator System, Esaote SpA, Genoa, Italy), and to assess the accuracy of targeting using a 22 gauge cytologic needle. The second phase of the study was to validate such a technique using a 15 gauge RF multitined expandable needle (RITA Medical Systems, Mountain View, CA) and to examine the accuracy of the needle placement relative to the target. The tip of the trocar of the RF needle had to be placed 1 cm from the target and then the hooks had to be deployed to 3 cm. Unenhanced CT of the liver and multiplanar reconstructions were performed to calculate accuracy of positioning, ie, the lateral distance between the needle and the target, the distance between the tip of the trocar of the RF electrode and the target, and the lateral distance between the central tine of the RF electrode and the target. RESULTS: All calf livers underwent successful CT-US registration with a mean registration error of 3.0 +/- 0.1 mm and 2.9 +/- 0.1 mm in the initial and second phase of the study, respectively. In the initial phase an overall number of 24 insertions were performed after the US-CT guidance. The mean needle to target distance was 1.9 +/- 0.7 mm (range, 0.8-3.0 mm). In the second phase an overall number of 12 ablations were performed. The mean target-trocar distance was 10.3 +/- 2.6 mm. The mean target-central tine lateral distance was 3.9 +/- 0.7 mm (range, 2.9-5.1 mm). After the dissection of the specimen the target was found unchanged in the center of the ablation zone in all cases. CONCLUSION: Real-time registration and fusion of preprocedure CT volume images with intraprocedure US is feasible and accurate. The study was however conducted in an ideal experimental setting, without patient movements and breathing, and further studies are warranted to validate the system under clinical conditions.     

Large-volume radiofrequency ablation of ex vivo bovine liver with multiple cooled cluster electrodes

Three methods of creating large thermal lesions with cool-tip cluster electrodes were compared. Three cluster electrodes were arranged 4 cm apart in a triangular array. Eight lesions were created ex vivo in fresh bovine liver (from a butcher) with each method: sequential ablation (three electrodes, 12 minutes each); simultaneous activation of electrodes (12 minutes); and rapid switching of power between electrodes (12 minutes), for which an electronic computer-controlled switch was developed. For sequential, rapid switching, and simultaneous methods, lesion volumes were 137.5 cm(3)+/- 22.2, 116.4 cm(3)+/- 15.2, and 22.3 cm(3)+/- 6.4 (P < .05), respectively, and final temperatures at lesion center were 80 degrees C +/- 5, 97 degrees C +/- 8, and 41 degrees C +/- 3 (P < .001), respectively. Because of electrical interference between electrodes, simultaneous method led to little heating at the center between the electrodes and created small discontinuous lesions. Rapid switching created large round lesions by employing multiple electrodes concurrently, which substantially reduced treatment time and resulted in more effective heating between electrodes.     

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.     

Porcine liver: morphologic characteristics and cell viability at experimental radiofrequency ablation with internally cooled electrodes

PURPOSE: To evaluate morphologic characteristics and cell viability of radiofrequency ablation zones in porcine liver. MATERIALS AND METHODS: Approval of the study protocol was obtained from the Ethics Committee on Use of Live Animals for Teaching and Research at University of Hong Kong. Internally cooled electrodes were used to produce 120 ablated zones ex vivo and 60 ablated zones in vivo with single electrodes (1-, 2-, and 3-cm exposed lengths) or clustered electrodes (1.0-, 2.0-, and 2.5-cm exposed lengths) at 4, 8, 12, and 16 minutes of ablation (ex vivo) and 8 and 12 minutes of ablation (in vivo). Morphologic measurements of each ablated zone were performed. Cell viability in each ablated zone was assessed qualitatively with histochemical staining and quantitatively with measurement of intracellular adenosine 5'-triphosphate (ATP) concentration. RESULTS: Exposed length of electrode (coefficient = 0.79, standard error = 0.04, P < .001), duration of ablation (coefficient = 0.14, standard error = 0.01, P < .001), and clustered electrode design (coefficient = 1.21, standard error = 0.05, P < .001) were independent factors that affected minimal transverse diameter and volume of ablated zone in ex vivo study. Similar morphologic characteristics existed among ablated zones in in vivo study. Mean distance of ablation beyond the electrode tip remained constant (ex vivo, 1.0 cm +/- 0.08 [standard deviation]; in vivo, 0.5 cm +/- 0.05) regardless of different ablation conditions. Histochemical staining revealed no viable hepatocytes from center to margins of white zone in each ablated area. Mean intracellular ATP concentration in margins of white zone (9.5 x 10(-12) mol/microg DNA +/- 1.43) was lower than that in red zone (4088 x 10(-12) mol/microg DNA +/- 65.97, P < .001) and in adjacent normal liver (4528 x 10(-12) mol/microg DNA +/- 52.74, P < .001). CONCLUSION: Distance of ablation beyond the tip of the electrode remained constant (ex vivo, 1.0 cm; in vivo, 0.5 cm) with different conditions of ablation. Complete and uniform cellular destruction was achieved in the white zone of ablated area.     

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.     

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.     

Saline-enhanced radiofrequency ablation of breast tissue: an in vitro feasibility study

RATIONALE AND OBJECTIVES: The feasibility of radiofrequency (RF) ablation for the treatment of breast tumors was investigated in vitro. The best parameters for ablation of breast tissue were chosen. METHODS: Saline-enhanced RF ablation was performed in human breast tissue specimens and cow udder tissue. Temperature profiles were measured depending on RF power (20, 28, 36 W) and NaCl infusion rate (15, 30, 60 mL/h) using eight thermocouples. Lesion development was monitored by ultrasound. Thermolysis efficiency was measured by tissue weight determinations before and after ablation. RESULTS: After RF ablation of tissue samples, 73.6% turned into a fat/saline emulsion. Ultrasound monitoring showed a cone-shaped hyperechoic area during the first 2 minutes of RF ablation, followed by an irregular expansion of the area. Time-dependent spatial temperature curves were more homogeneous at low infusion rates (15 mL/h). Peak temperatures up to 160 degrees C were measured. CONCLUSIONS: Controlled RF ablation of breast tissue is feasible. The irregular expansion of RF lesions in fatty breast tissue is due to liquefied fat. Low saline interstitial infusion rates result in better control of lesioning.     

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.     

射频消融联合无水乙醇注射在兔肝脏中的实验研究

目的 研究不同方式的射频消融(RFA)与无水乙醇注射(PEI)联合应用对正常兔肝脏的消融效果,并评价其安全性和实用性.方法 采用32只活体新西兰大白兔正常肝脏进行研究,分为4组,各组分别采用RFA-PEI(A组)、PEI-RFA(B组)、RFA(C组)和PEI(D组)处理,并于术前,术后1、3、7d抽血检查丙氨酸转氨酶(ALT)、天冬氨酸转氨酶(AST)、血清肌酐(Cr)水平的变化情况.术后各组行肝脏增强CT扫描,计算各组消融灶体积.结果 术前各组血清ALT、AST、Cr水平差异无统计学意义(P＞0.05);术后1d各组血清ALT、AST与术前差异有统计学意义(P＜0.05);术后3d各组血清ALT、AST水平开始下降,术后7d各组ALT、AST与术前差异无统计学意义(P＞0.05),术后1、3、7d各组血清Cr与术前比较均差异无统计学意义(P＞0.05).A、B、C和D组的消融体积分别为(3.10 ± 1.10)mm3、(5.99±2.23)mm3、(0.77±0.15)mm3和(0.15±0.07)mm3,B组显著大于A、C和D组(P＜0.05).结论 PEI后RFA对于兔肝、肾功能影响小、并发症少,PEI-RFA治疗安全、有效;PEI-RFA组产生的消融体积明显大于RFA后PEI组、RFA组、PEI组的消融体积.     

经皮射频消融术治疗椎体肿瘤合适消融时间的实验研究

目的 探索经皮射频消融术(RFA)治疗兔椎体肿瘤模型不同消融时间的疗效及安全性.方法 采用CT引导经皮穿刺法将VX2瘤块接种入新西兰大白兔的腰椎内,成功建立20只兔椎体肿瘤模型.将其随机分为A、B两组,每组10只.测量肿瘤椎体的核素标准化摄取值(stand uptake value,SUV),然后对实验动物行消融治疗.A组消融持续时间3 min,B组为5 min,观察治疗后24 h动物急性瘫痪发生情况.治疗后第1天和第7天,实验动物再次接受PET-CT检查,测定椎体肿瘤的SUV值,然后取肿瘤标本行病理检查.比较两组动物RFA术后的瘫痪率以及治疗前后不同时间点的肿瘤SUV值有无差异.结果 A、B两组动物射频后的瘫痪发生率差异有统计学意义(1/10比6/10、P＜0.05).两组肿瘤模型消融前的SUV值分别为4.60±0.47、4.48±0.45,治疗后第1天分别为0.94±0.08、0.92±0.07,治疗后第7天分别为0.93±0.04、0.95±0.06.两组椎体肿瘤的SUV值在治疗前、后差异有统计学意义(F=3 257.87、P＜ 0.05),两组之间则差异无统计学意义.病理结果显示两组肿瘤模型的肿瘤细胞明显坏死,均未见明显残存肿瘤细胞.结论 应用RFA治疗兔椎体肿瘤,消融时间持续3 min已能有效杀伤椎体肿瘤细胞,且严重并发症的概率小.延长消融时间疗效无显著增加,但可能增加神经损伤的风险.