Radiofrequency tissue ablation with a cooled needle in vitro: Ultrasonography, dose response, and lesion temperature

Rationale and Objectives. Radiofrequency (RF) tissue ablation with a cooled needle electrode (probe) can produce large lesions, By using this technique on ex vivo calf livers, the authors evaluated the role of ultrasound (US), dose response, and temperature course with time. Methods. RF ablation was produced with a 14-gauge probe with a 2-cm exposed tip. The lesions were examined with US and macroscopically after various treatment durations. Tissue temperature was measured with thermosensors inserted 1, 2, and 3 cm from the probe. Results. Before treatment the tip of the probe was easy to visualize with US, but during treatment microbubbles obscured the lesion and probe. After treatment, the lesions appeared hypoechoic. Lesion size was underestimated based on US findings. Lesion size was logarithmically correlated to treatment duration. Lesion temperature increased at an increased rate with higher wattage applied and with decreased distance from the probe. Conclusion. US is useful for probe placement before treatment and might be of value after treatment. Lesion size increases reproducibly with treatment duration.