Korean J Radiol.  2003 Jun;4(2):117-123. 10.3348/kjr.2003.4.2.117.

Overlapping Ablation Using a Coaxial Radiofrequency Electrode and Multiple Cannulae System: Experimental Study in ex-Vivo Bovine Liver

• Choi D
• Kim SK
• Lim HK
• Kim MJ
• Lee J
• Kim EY
• Kim S
• Kim SH

• KMID: 1118814
• DOI: http://doi.org/10.3348/kjr.2003.4.2.117

Abstract

OBJECTIVE
To assess the sizes and configurations of thermal zones after overlapping ablations using a coaxial radiofrequency (RF) electrode and multiple cannulae in ex-vivo bovine liver. MATERIALS AND METHODS: For ablation procedures, a coaxial RF electrode and introducer set was used. Employing real-time ultrasound guidance and overlapping techniques in explanted, fresh bovine liver, we created five kinds of thermal zones with one (n=10), two (n=8), four (n=3), and six ablation spheres (n=3). Following ablation, MR images were obtained and the dimensions of all thermal zones were measured on the longitudinal or transverse section of specimens. The shape of the composite ablation zones was evaluated using three-dimensional MR image reconstruction. RESULTS: At gross pathologic examination of ten single-ablation zones (spheres), the long-axis (transverse) and short-axis lengths of zones ranged from 3.7 to 4.4 (mean, 4.1) cm and from 3.5 to 4.0 (mean, 3.7) cm, respectively. The long-axis (transverse) and short-axis lengths of double-ablation zones (cylinders) with 23% overlap ranged from 7.0 to 7.7 (mean, 7.3) cm and from 3.0 to 3.9 (mean, 3.5) cm, respectively; those with 58% overlap ranged from 6.0 to 6.4 (mean, 6.2) cm and from 3.8 to 4.6 (mean, 4.3) cm, respectively. The long-axis (diagonal) and short-axis lengths on a transverse section of four-ablation zones (cakes) ranged from 8.5 to 9.7 (mean, 9.1) cm and from 3.0 to 4.1 (mean, 3.7) cm, respectively. Gross pathologic examination of three composite six-ablation zones (spheres) showed that the long-axis (diagonal) and short-axis lengths of zones ranged from 9.0 to 9.9 (mean, 9.4) cm and from 6.8 to 7.5 (mean, 7.2) cm, respectively. T2-weighted MR images depicted low-signal thermal zones containing multiple curvilinear and spotty regions of hyperintensity. CONCLUSION: Using a coaxial RF electrode and multiple cannulae, together with ultrasound guidance and precise overlapping ablation techniques, we successfully created predictable thermal zones in ex-vivo bovine liver.

Keyword

Radiofrequency (RF) ablation; Liver, interventional procedure; Animals

Figure

• 

  Fig. 1 Photograph of a radiofrequency (RF) system (LeVeen CoAccess Electrode System, RadioTherapeutics Corporation, Mountain View, Cal., U.S.A.). At the tip of the 16-gauge outer electrode, ten hookshaped, retractable electrodes (top) are seen fully deployed (3.5 cm). Also visible are a cannula (bottom) and stylet (middle).

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  Fig. 2 Ultrasound image of bovine liver depicts the tips (arrows) of two cannulae inserted using introducer sets prior to RF ablation. On two hyperechoic tips, posterior acoustic shadowing is visible.

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  Fig. 3 A single-ablation zone. A. Photograph of longitudinal section of the specimen, obtained within 60 minutes of RF ablation, shows an ablation zone (arrows) measuring 4.1 cm transversely and 4.0 cm longitudinally. B. T2-weighted fast spin-echo (FSE) (TR 3084/TE 104) coronal image depicts a low-signal thermal zone (arrows) with multiple curvilinear and spotty regions of hyperintensity (arrowhead), probably indicative of hemorrhagic products at hook insertion sites. C. Three-dimensional ablation zone reconstructed from MR images appears as an irregularly contoured sphere.

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  Fig. 4 A double-ablation zone created by overlapping ablation spheres by 23% of their diameter (interval between electrode tips: 3.2 cm). A. Photograph of longitudinal section of the specimen shows an ablation zone with a fissure (curved arrow) measuring 7.4 cm transversely and 4.0 cm longitudinally. It is delimited by three concentric areas: a pale central core, middle hemorrhagic or red rim (arrowhead), and an outer pink rim (arrow) of variable thickness that merges with normal liver. B. T2-weighted FSE (TR 3084/TE 104) coronal image depicts a low-signal zone (arrows). C. Three-dimensional ablation zone reconstructed from MR images appears as a composite ellipsoid with no definite fissure.

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  Fig. 5 A double-ablation zone created by overlapping ablation spheres by 58% of their diameter (interval between electrode tips: 1.7 cm). A. Photograph of longitudinal section of the elliptical specimen depicts an ablation zone measuring 6.4 cm transversely and 4.2 cm longitudinally. B. T2-weighted FSE (TR 3084/TE 104) coronal image shows a low-signal zone (arrows). C. Three-dimensional ablation zone reconstructed from MR images appears as an irregularly contoured composite oval shape.

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  Fig. 6 A four-ablation zone created by rectangularly overlapping ablation spheres by 23% of their diameter (interval between electrode tips: 3.2 cm). A. Photograph of transverse section of the irregular square-shaped specimen depicts an ablation zone measuring 9.0 cm diagonally. B. T2-weighted FSE (TR 5200/TE 104) axial image shows a low-signal zone (arrows). C. Three-dimensional ablation zone reconstructed from MR images appears as an irregularly contoured composite square cake.

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  Fig. 7 A six-ablation zone designed with four spheres in the x-y plane and two along the z-axis, with ablation spheres which overlap by 23% of their diameter. A. Photograph of longitudinal section of the oval-shaped specimen depicts an ablation zone. B. T2-weighted FSE (TR 5067/TE 102) coronal image shows a low-signal zone (arrows). C. Three-dimensional ablation zone reconstructed from MR images appears as a composite zone (irregularly contoured sphere), with no definite pits at the junction of the three small spheres.

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