RADIOFREQUENCY TISSUE ABLATION WITH A COOLED NEEDLE IN-VITRO - ULTRASONOGRAPHY, DOSE-RESPONSE, AND LESION TEMPERATURE

Rationale and Objectives. Radiofrequency (RF) tissue ablation with a c ooled needle electrode (probe) can produce large lesions, By using thi s technique on ex vivo calf livers, the authors evaluated the role of ultrasound (US), dose response, and temperature course with time. Meth ods. RF ablation was produced with a 14-gauge probe with a 2-cm expose d tip. The lesions were examined with US and macroscopically after var ious treatment durations. Tissue temperature was measured with thermos ensors inserted 1, 2, and 3 cm from the probe. Results. Before treatme nt the tip of the probe was easy to visualize with US, but during trea tment 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 d uration. Lesion temperature increased at an increased rate with higher wattage applied and with decreased distance from the probe. Conclusio n. US is useful for probe placement before treatment and might be of v alue after treatment. Lesion size increases reproducibly with treatmen t duration.