Radiofrequency Renal Ablation: In Vivo Comparison of Internally Cooled, Multitined Expandable and Internally Cooled Perfusion Electrodes

How does saline backflow affect the treatment of saline-infused radiofrequency ablation?

BACKGROUND AND OBJECTIVE

Saline infusion is applied together with radiofrequency ablation (RFA) to enlarge the ablation zone. However, one of the issues with saline-infused RFA is backflow, which spreads saline along the insertion track. This raises the concern of not only thermally ablating the tissue within the backflow region, but also the loss of saline from the targeted tissue, which may affect the treatment efficacy.

METHODS

In the present study, 2D axisymmetric models were developed to investigate how saline backflow influence saline-infused RFA and whether the aforementioned concerns are warranted. Saline-infused RFA was described using the dual porosity-Joule heating model. The hydrodynamics of backflow was described using Poiseuille law by assuming the flow to be similar to that in a thin annulus. Backflow lengths of 3, 4.5, 6 and 9 cm were considered.

RESULTS

Results showed that there is no concern of thermally ablating the tissue in the backflow region. This is due to the Joule heating being inversely proportional to distance from the electrode to the fourth power. Results also indicated that larger backflow lengths led to larger growth of thermal damage along the backflow region and greater decrease in coagulation volume. Hence, backflow needs to be controlled to ensure an effective treatment of saline-infused RFA.

CONCLUSIONS

There is no risk of ablating tissues around the needle insertion track due to backflow. Instead, the risk of underablation as a result of the loss of saline due to backflow was found to be of greater concern.

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.

Application of Radiofrequency Ablation of Renal VX2Tumors by Cooled-Tip Electrode in a Rabbit Model

Objective. This study has two purposes: (a) to compare the use of tumor cell suspensions and excised tumor tissue for generating renal tumors suitable for radiofrequency ablation (RFA) studies and (b) to assess the efficacy of RFA for ablation of renal VX2 tumors in a rabbit model. Procedures. VX2 tumor masses were used to inoculate 17 rabbits. The renal VX2 tumors of 13 rabbits were subsequently treated with a cooled-tip RF system at a power of 15-30 W for 3-6 minutes, and 4 rabbits served as control. After RFA, rabbits were observed by contrast-enhanced CT to ascertain the ablative range. Rabbits were divided into three groups and sacrificed at 3, 7, and 14 days post-treatment for histopathological studies. Results. Both tumor implant methods had a 100% success rate in generating tumors. The average lesion produced was 1.3x1.8x1.5 cm. Complete tumor ablation occurred in 76.9%, and local tumor growth in 23.1%. Depending on the position of the tumors, the complications after RFA treatment included infarction, perirenal hematoma, hydronephrosis, and abscess. The over-all complication rate was 38.5%. In histopathological studies, a central needle track, tumor coagulation, renal tissue coagulation, peripheral hemorrhage, and an inflammatory layer could be observed. Conclusion and clinical relevance. Application of RFA to destroy renal VX2 tumors in this rabbit model has a relatively high cure rate. It can be used to destroy small renal tumors in a precise and non-invasive manner. Impact on human medicine. We hope to apply this procedure in selected human renal tumors in the future.

High intensity focused ultrasound: physical principles and devices

High intensity focused ultrasound (HIFU) is gaining rapid clinical acceptance as a treatment modality enabling non-invasive tissue heating and ablation for numerous applications. HIFU treatments are usually carried out in a single session, often as a day case procedure, with the patient either fully conscious, lightly sedated or under light general anaesthesia. A major advantage of HIFU over other thermal ablation techniques is that there is no necessity for the transcutaneous insertion of probes into the target tissue. The high powered focused beams employed are generated from sources placed either outside the body (for treatment of tumours of the liver, kidney, breast, uterus, pancreas and bone) or in the rectum (for treatment of the prostate), and are designed to enable rapid heating of a target tissue volume, while leaving tissue in the ultrasound propagation path relatively unaffected. Given the wide-ranging applicability of HIFU, numerous extra-corporeal, transrectal and interstitial devices have been designed to optimise application-specific treatment delivery. Their principle of operation is described here, alongside an overview of the physical mechanisms governing HIFU propagation and HIFU-induced heating. Present methods of characterising HIFU fields and of quantifying HIFU exposure and its associated effects are also addressed.