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Technical Briefs

A Microwave Surface Applicator for Tissue Coagulation: Technical Characteristics and Performances

[+] Author and Article Information
Benjamin Lepers1

Engineer Dr IngDepartment of Physics,  Institut de Physique Hubert Curien, Strasbourg, France,benjamin.lepers@gmail.com

Peter Clegg

Department of Physics,  Bath University, Bath, United KingdomP.J.Clegg@bath.ac.uk

Nigel Cronin

Department of Physics,  Bath University, Bath, United KingdomN.J.Cronin@bath.ac.uk

Ines Wieland

Department of Physics,  Bath University, Bath, United Kingdomines.wieland@gmail.com

1

Corresponding author.

J. Med. Devices 6(1), 014502 (Mar 13, 2012) (6 pages) doi:10.1115/1.4005782 History: Received March 04, 2011; Revised December 19, 2011; Published March 12, 2012; Online March 13, 2012

This work describes the mechanical and the electromagnetic design of a microwave surface applicator used to coagulate liver tissue in the treatment of hepatic tumors. A good prediction of the ratio between reflected and forward microwave power (return loss) is obtained with a finite element model using commercial software. Laboratory testing of the applicator performed in polyacrylamide gel (PAG) and in ex vivo bovine liver show a hemispherical heat distribution pattern and hemispherical ablations up to 20 mm in diameter and 15 mm in depth in a controlled manner in 1 min. The applicator can also be used to coagulate larger areas of tissue with 2–5 mm depth by moving the applicator on the surface of the tissue. Experimental results indicate that the coagulated volume of tissue is approximately proportional to the energy delivered into ex vivo bovine liver, hemispherical in shape, obtained in short time duration with a volumetric rate of coagulated tissue of about 50 mm3 /s.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Assembly design of the surface microwave applicator

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Figure 2

Surface microwave applicator. From left to right: N type connector, handle, metallic tube, waveguide, and ceramic.

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Figure 3

Surface applicator connected to the flexible coaxial cable connected to the 2.45 GHz microwave generator

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Figure 4

|S11| versus frequency at the ceramic port surface in distilled water. Measurements are shown in blue; finite element calculations in red.

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Figure 5

Specific absorption rate in tissue around the surface applicator aperture

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Figure 6

Heating patterns of the microwave surface applicator. The microwave field is emitted from the ceramic face and propagates through the phantom tissue polyacrylamide gel (PAG). The white cloud shows a temperature elevation of the load material of above 40 and 50 °C, which allows visualizing of the heating pattern of the surface applicator. The volume of heated material increased with the duration of power application, see (a) to (f).

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Figure 7

Typical cross sections of the ablations in ex vivo bovine liver for 80 to 100 W power range and 20 to 60 s time period

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Figure 8

Ablated volume (cm3 ) versus input energy (J) for ex vivo bovine liver ablations of Table 2. The graph shows a linear relationship between ablated volume and energy input.

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Figure 9

Pig liver surface coagulation with the applicator

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Figure 10

Cut through the liver, depth of coagulation from a square surface of 5 cm × 5 cm was coagulated to 2 mm to 5 mm

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