Radiofrequency hepatic ablation with internally cooled electrodes and hybrid applicators with distant saline infusion using an in vivo porcine model

Increasing radiofrequency ablation volumes with the use of internally cooled electrodes and injected hydrochloric acid in ex vivo bovine livers

PURPOSE

We used an impedance-controlled generator with an internally cooled electrode to perform radiofrequency ablation (RFA) in ex vivo bovine livers, with a single injection of either 38.5% sodium chloride (NaCl) or 10% hydrochloric acid (HCl), to determine the relative effects of these two solutions on tissue impedance, temperature and ablation volume.

MATERIALS AND METHODS

We performed 10 ablations each with injections of NaCl (NaCl-RFA), HCl (HCl-RFA) or nothing (RFA-alone), with a power setting of 200 W for 15 minutes. We recorded tissue impedance before and after injection. We logged temperatures obtained from thermocouple probes positioned 5, 10, 15 and 20 mm from the internally cooled RF electrode. After ablation, we measured ablation zone longitudinal and transverse diameters, and we calculated a spherical ratio (SR) for each ablation.

RESULTS

Mean post-injection impedance of 30.3 (standard deviation [SD] 2.5) ohms for HCl was significantly lower than that of 55.4 (SD 3.5) ohms for NaCl (p < .001). Mean maximum temperatures recorded at each respective distance from the RFA electrode were all highest for HCl-RFA and lowest for RFA-alone (p < .001). Mean longitudinal and transverse diameters after HCl-RFA (5.50 [SD 0.25] cm and 5.28 [SD 0.22] cm, respectively) were significantly larger than those after NaCl-RFA (4.24 [SD 0.35] cm and 3.55 [SD 0.43] cm, respectively) and after RFA-alone (3.60 [SD 0.10] cm and 2.70 [SD 0.13] cm, respectively) (p < .001). Mean SR after HCl-RFA (0.93, SD 0.02) was significantly higher than mean SR after NaCl-RFA (0.76, SD 0.06) and RFA-alone (0.72, SD 0.04) (p < .001).

CONCLUSION

Monopolar, impedance-controlled RFA, with an internally cooled electrode and a single 10% HCl injection may allow larger tumors to be treated, potentially resulting in improved patient outcomes.

Chronological changes of radiofrequency ablation zone in rabbit liver: an in vivo correlation between gross pathology and histopathology

OBJECTIVE

To examine the gross pathology and histopathology of ablation zones created from radiofrequency (RF) ablation and to correlate their chronological changes.

METHODS

A total of 48 in vivo ablation zones (16 rabbit livers) were obtained immediately after and also 30 min, 1 h and 2 h after RF ablation and were subjected to haematoxylin and eosin (H&E) staining, nicotinamide adenine dinucleotide (NADH) diaphorase staining, terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) staining. Chronological changes in gross pathology and histopathology were evaluated and correlated with each other.

RESULTS

Peripheral red zones on gross pathology correlated with peripheral zones on H&E staining, lightly stained peripheral zones on NADH staining and peripheral positive zones on TUNEL staining. Central white zones on gross pathology correlated with combined central and border zones on H&E staining, central negative zones on NADH staining and combined central-positive and middle-negative zones on TUNEL staining. Boundary visibility between central white and peripheral red zones on gross pathology was significantly higher at 1 and 2 h than immediately after RF ablation. As time increased after RF ablation, visibility of the border zone on H&E staining and the grade of positively stained hepatocytes in the peripheral zone on TUNEL staining increased.

CONCLUSION

Chronological changes in gross pathology of RF ablation zones correlated well with histopathology. The boundary between the central white and peripheral red zones tended to become clear at 1 h after RF ablation. Advances in knowledge: (1) RF ablation zones show chronological changes on gross pathology and histopathology. (2) Gross pathology and histopathology correlate well with each other.

Current status and prospective of imaging guided radiofrequency ablation in medium to large sized hepatocellular carcinomas

The incidence of liver cancer is high in China and effective treatments are required. Recently, imaging guided radiofrequency ablation (RFA) has become increasingly accepted in treating solid tumors because of minimal invasiveness, easy operation and effectiveness. The outcome of RFA in small liver tumors is even comparable to that of surgery. However, the RFA efficacy in larger ( > 3.0 cm) liver tumors is not satisfactory and recurrence after treatment is common. The development of basic research and RFA device has provided more opportunities for us to treat>3.0 cm liver tumors. The successful ablation of solid tumors relies on three key components, the technology (i.e., the RFA generator and electrodes selected), the biology of the tumor and background tissue, and operator factors. The current development and prospective of the three main elements will be the focus in this review.

Ex Vivo Liver Experiment of Hydrochloric Acid-Infused and Saline-Infused Monopolar Radiofrequency Ablation: Better Outcomes in Temperature, Energy, and Coagulation

OBJECTIVE

To compare temperature, energy, and coagulation between hydrochloric acid-infused radiofrequency ablation (HAIRFA) and normal saline-infused radiofrequency ablation (NSIRFA) in ex vivo porcine liver model.

MATERIALS AND METHODS

30 fresh porcine livers were excised in 60 lesions, 30 with HAIRFA and the other 30 with NSIRFA. Both modalities used monopolar perfusion electrode connected to a RF generator set at 103 °C and 30 W. In each group, ablation time was set at 10, 20, or 30 min (10 lesions from each group at each time). We compared tissue temperatures (at 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 cm away from the electrode tip), average power, deposited energy, deposited energy per coagulation volume (DEV), coagulation diameters, coagulative volume, and spherical ratio between the two groups.

RESULTS

Temperature-time curves showed that HAIRFA provided progressively greater heating than that of NSIRFA. At 30 min, mean average power, deposited energy, coagulation volumes (113.67 vs. 12.28 cm(3)) and diameters, and increasing in tissue temperature were much greater with HAIRFA (P < 0.001 for all), except DEV was lower (456 vs. 1396 J/cm(3), P < 0.001). The spherical ratio was closer to 1 with HAIRFA (1.23 vs. 1.46). Coagulation diameters, volume, and average power of HAIRFA increased significantly with longer ablation times. While with NSIRFA, these characteristics were stable till later 20 min, except the power decreased with longer ablation times.

CONCLUSIONS

HAIRFA creates much larger and more spherical lesions by increasing overall energy deposition, modulating thermal conductivity, and transferring heat during ablation.

Distant infusion of saline may enlarge coagulation volume during radiofrequency ablation of liver tissue using cool-tip electrodes without impairing predictability

OBJECTIVE

Our aim was to evaluate the capability of a Cool-tip electrode to create larger coagulation volumes combined with a low-flow (0.1 mL/min) perfusion of hypertonic saline at a distance of 2 mm (hybrid applicator) without reducing either predictability or sphericity of the coagulation zone.

MATERIALS AND METHODS

A total of 48 radiofrequency ablations were performed on a total of 12 adult pigs: 24 with the Cool-tip (group 1) and 24 with the hybrid applicator (group 2). Volumes and diameters were assessed both macroscopically and with imaging techniques (ultrasound and MRI). Digital reconstruction techniques were also used. Reproducibility of the coagulations was assessed by means of the coefficient of variation.

RESULTS

The macroscopic assessment showed a significantly larger coagulation zone in group 2 than in group 1, both with (19.40 ± 11.38 cm(3) vs 9.16 ± 5.62 cm(3); p < 0.001) and without (19.54 ± 11.39 cm(3) vs 9.21 ± 5.74 cm(3); p < 0.001) digital reconstruction. Differences were also significant in the MRI assessment. The minimum transverse diameter was also significantly (p < 0.01) larger in group 2 than group 1: 2.46 ± 0.61 versus 1.86 ± 0.55 cm for macroscopic assessment, 2.33 ± 0.96 versus 1.69 ± 0.53 cm for ultrasound, and 2.41 ± 0.58 versus 1.8 ± 0.52 cm for MRI. The coefficient of variation was similar in both groups.

CONCLUSION

The results suggest that low-flow perfusion of hypertonic saline at 2 mm from a Cool-tip electrode could increase coagulation zone volume without reducing predictability.

Radioablation settings affecting the size of lesions created ex vivo in porcine livers with monopolar perfusion electrodes

RATIONALE AND OBJECTIVES

To explore the morphological characteristics of ablated lesions and find which combination of duration, temperature, and power was preferable to create largest lesion size with monopolar perfusion electrodes.

MATERIALS AND METHODS

Using monopolar perfusion electrodes to create 72 lesions in 30 excised porcine livers with radiofrequency radiation at different durations (5, 10, 15, and 20 minutes), temperatures (83 degrees C, 93 degrees C, 103 degrees C, and 113 degrees C), and powers (20, 30, and 40 W). Lesion volumes were calculated from longitudinal diameters and transverse diameters. Morphological characteristics were assessed microscopically from slides stained with hematoxylin and eosin.

RESULTS

Positive correlations were found between duration and longitudinal diameter (r = 0.66; P < .001), transverse diameter (r = 0.66; P < .001), distance of ablation beyond the electrode tip (r = 0.56; P < .001), and volume of lesions (r = 0.66; P < .001). Temperature was also positively correlated with longitudinal diameter (r = 0.70; P < .001), transverse diameter (r = 0.72; P < .001), distance of ablation beyond the electrode tip (r = 0.61; P < .001), and lesion volume (r = 0.711; P < .001). Lesion size did not increase when duration was longer than 15 minutes and temperature was higher than 103 degrees C. Power was not correlated with lesion size. Lesion size did not increase with increasing power. Macroscopically, all lesions were elliptical in cross section and appeared three zones: a central zone (I), a coagulated necrotic zone (II), and a hemorrhagic and edematous zone (III) from inside to outside. Microscopically, cells morphology and the nucleus were irregular or even disappeared in zone I. In zone II and III, cells did not appear deformation.

CONCLUSION

Duration and temperature, not power, affected lesion size. The largest lesion size was about 3.5 cm x 2.5 cm x 2.5 cm as temperature and duration was 15 minutes/103 degrees C.

Microwave ablation: An experimental comparative study on internally cooled antenna versus non-internally cooled antenna in liver models

RATIONAL AND OBJECTIVES

Microwave ablation is an alternative therapy with high cost-effectiveness for liver malignancy. The authors designed this experiment to compare the effect of microwave ablation using a non-internally cooled (NIC) antenna with that using an internally cooled (IC) antenna in both an ex vivo and an in vivo liver models.

MATERIALS AND METHODS

Sixty-two microwave ablations were performed in ex vivo porcine and in vivo canine liver models (NIC antenna, 28 coagulations; IC antenna, 34 coagulations). Pair comparisons were executed in terms of the coagulation parameters, including short-axis diameter (SD), long-axis diameter (LD), and spherical ratio (SR, SD/LD). The distributions of tissue temperatures were compared in ex vivo ablation. During in vivo ablation, the temperatures of antenna shaft were measured and unintended tissue coagulation were observed and compared.

RESULTS

In both ex vivo and in vivo ablations, less charring areas were found around the IC antenna shaft. With a longer SD (P < .01) and a shorter LD (P < .01), the coagulations of IC antenna appeared to be more spherical than those of NIC antenna (P < .01). During ablations in vivo, the temperatures of NIC antennas shaft were up to 90 degrees C or even higher, which resulted in some unintended tissue coagulation, whereas the temperatures of IC antennas shaft were lower than 20 degrees C in all ablation processes without any unintended tissue coagulation (P < .01).

CONCLUSION

The IC antenna performed better than NIC antenna in microwave ablation for liver models and might be more suitable for therapy for liver malignancy in clinical practice.

Algorithm optimization for multitined radiofrequency ablation: comparative study in ex vivo and in vivo bovine liver

PURPOSE

To prospectively optimize multistep algorithms for largest available multitined radiofrequency (RF) electrode system in ex vivo and in vivo tissues, to determine best energy parameters to achieve large predictable target sizes of coagulation, and to compare these algorithms with manufacturer's recommended algorithms.

MATERIALS AND METHODS

Institutional animal care and use committee approval was obtained for the in vivo portion of this study. Ablation (n = 473) was performed in ex vivo bovine liver; final tine extension was 5-7 cm. Variables in stepped-deployment RF algorithm were interrogated and included initial current ramping to 105 degrees C (1 degrees C/0.5-5.0 sec), the number of sequential tine extensions (2-7 cm), and duration of application (4-12 minutes) for final two to three tine extensions. Optimal parameters to achieve 5-7 cm of coagulation were compared with recommended algorithms. Optimal settings for 5- and 6-cm final tine extensions were confirmed in in vivo perfused bovine liver (n = 14). Multivariate analysis of variance and/or paired t tests were used.

RESULTS

Mean RF ablation zones of 5.1 cm +/- 0.2 (standard deviation), 6.3 cm +/- 0.4, and 7 cm +/- 0.3 were achieved with 5-, 6-, and 7-cm final tine extensions in a mean of 19.5 min +/- 0.5, 27.9 min +/- 6, and 37.1 min +/- 2.3, respectively, at optimal settings. With these algorithms, size of ablation at 6- and 7-cm tine extension significantly increased from mean of 5.4 cm +/- 0.4 and 6.1 cm +/- 0.6 (manufacturer's algorithms) (P <.05, both comparisons); two recommended tine extensions were eliminated. In vivo confirmation produced mean diameter in specified time: 5.5 cm +/- 0.4 in 18.5 min +/- 0.5 (5-cm extensions) and 5.7 cm +/- 0.2 in 21.2 min +/- 0.6 (6-cm extensions).

CONCLUSION

Large zones of coagulation of 5-7 cm can be created with optimized RF algorithms that help reduce number of tine extensions compared with manufacturer's recommendations. Such algorithms are likely to facilitate the utility of these devices for RF ablation of focal tumors in clinical practice.

Radiofrequency ablation of large size liver tumours using novel plan-parallel expandable bipolar electrodes: initial clinical experience

PURPOSE

Although radiofrequency ablation (RFA) is a promising method for local treatment of liver malignancies, with conventional monopolar systems recurrence rates for large size tumours (≥3.5 cm) remain high. The objective of this study was to evaluate the safety, feasibility and local effectiveness of a novel bipolar plan-parallel expandable system for these larger tumours.

METHODS AND MATERIALS

Eight consecutive patients with either unresectable colorectal liver metastases (CRLM in 6 patients), carcinoid liver metastases (1 patient) and hepatocellular carcinoma (HCC in 1 patient) of ≥3.5 cm were treated with bipolar RFA during laparotomy with ultrasound guidance. Early and late, major and minor complications were recorded. Local success was determined on 3-8 month follow-up CT scans of the upper abdomen.

RESULTS

Nine CRLM, one carcinoid liver metastases and one HCC (3.5-6.6 cm) were ablated with bipolar RFA. Average ablation time was 16 min (range 6-29 min.). Two patients developed a liver abscess which required re-laparotomy. In both cases bowel surgery during the same session probably caused bacterial spill. There were no mortalities. The patients were released from hospital between 5 and 29 days after the procedure (median 12 days). The 6-12 month follow-up PET-CT scans showed signs for marginal RFA-site tumour recurrence in three patients with CRLM (3/11 lesions).

CONCLUSION

Preliminary results suggest bipolar RFA to be a reasonably safe, fast and feasible technique which seems to improve local control for large size hepatic tumour ablations.