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Microwave Ablation with Loop Antenna: In Vivo Porcine Liver Model¹

¹ From the Departments of Radiology (S.A.S., L.A.S., T.C.W., F.T.L.), Surgery (K.M., A.S.W., D.M.M.), Pathology and Laboratory Medicine (T.F.W.), and Biostatistics (J.P.F.), University of Wisconsin Hospitals and Clinics, E3/311 Clinical Science Center, 600 Highland Ave, Madison, WI 53792. Received October 18, 2002; revision requested January 7, 2003; final revision received May 13; accepted August 14. Supported in part by Vivant Medical, Mountain View, Calif. Address correspondence to F.T.L. (e-mail: ftlee@wisc.edu).

PURPOSE: To determine the effectiveness of tissue ablation with a loop microwave antenna in various configurations in porcine liver tissue.

MATERIALS AND METHODS: Microwave energy was applied for 7 minutes at 60 W in six porcine livers (mean weight, 68.2 kg) by using single (n = 7) or dual 2.7-cm loop microwave probes in parallel (n = 9) or orthogonal (n = 9) configurations. Volume, diameter, shape, and temperature of the zone of necrosis and the presence of viable tissue inside the loop were determined and compared by means of factorial analysis of variance.

RESULTS: Mean lesion volume and maximum diameter, respectively, were 32.2 cm³ ± 14.4 (SD) and 4.6 cm ± 1.4 for lesions ablated with parallel probes (parallel lesions), 29.5 cm³ ± 8.1 and 4.3 cm ± 0.6 for lesions ablated with orthogonal probes (orthogonal lesions), and 6.4 cm³ ± 1.9 and 3.4 cm ± 0.62 for lesions ablated with single probes (single lesions) (P < .05, single vs parallel and orthogonal lesions). Mean minimum diameter was greatest for orthogonal lesions (3.5 cm ± 0.53; P = .017, parallel vs orthogonal lesions). Orthogonal lesions had the highest mean internal temperature (97.2°C) versus parallel (91.9°C) and single (60.0°C) lesions. All orthogonal lesions heated to 60°C in comparison to eight of nine parallel and four of seven single lesions. The mean time to reach 60°C was shortest for orthogonal lesions (93.3 seconds) versus parallel (123.8 seconds) and single (263.0 seconds) lesions. Orthogonal lesions were the most spherical. Viable tissue was present in the center of five of seven single, six of nine parallel, and zero of nine orthogonal lesions.

CONCLUSION: Loop microwave antennas allow precise control and effective ablation of targeted tissue, particularly in the orthogonal configuration.

© RSNA, 2004

Index terms: Animals • Liver neoplasms, therapy • Microwaves • Radiofrequency (RF) ablation

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