Elsevier

Academic Radiology

Volume 17, Issue 7, July 2010, Pages 894-899
Academic Radiology

Laboratory investigation
Microwave Ablation: An Experimental Comparative Study on Internally Cooled Antenna versus Non-internally Cooled Antenna in Liver Models

https://doi.org/10.1016/j.acra.2010.03.005Get rights and content

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°C or even higher, which resulted in some unintended tissue coagulation, whereas the temperatures of IC antennas shaft were lower than 20°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.

Section snippets

Microwave Ablation System

The microwave delivery system (FORSEA; Qinghai Microwave Electronic Institute, Nanjing, China) consists of an MTC-3 microwave generator with frequency of 2450 MHz and power output of 5–95 W, a flexible coaxial cable, a water pump, and a 14-gauge microwave antenna (Fig 1).

We used two types of antennas respectively connected with the same microwave generator through flexible coaxial cable. The NIC and IC antennas (Fig 2) both consist of a 10-cm long cable connection, a 16.5-cm long shaft coated

Ex Vivo Porcine Liver Ablation

Table 1 lists the parameters of ablation zones. The ablation zones of IC antenna had shorter LD and greater SD, and the shapes were more spherical (Fig 3). There were significant differences between the two types of antennas in SD (P < .01), LD (P < .01), and SR (P < .01). There was more charring around the NIC antenna than that around the IC antenna in each ablation lesion.

During each ablation with NIC antenna, the maximum temperature of the antenna shafts (ie, the surface temperature) was up

Discussion

In the past, the temperature of antenna shaft in microwave ablation would rise dramatically with the increase of treatment power in a very short duration and resulted in severe tissue and skin burns and unbearable pains. In addition, the shape of the ablation zone was ellipsoidal (the LD was greater than SD), which was not the optimal shape for tumor therapy; the ideal shape for tumor ablation was spherical. Therefore, the treatment duration was limited to a very short period, the output power

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