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DOI: 10.1148/radiol.2413051526
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(Radiology 2006;241:746-752.)
© RSNA, 2006

Experimental Studies

MR-guided Radiofrequency Ablation: Do Magnetic Fields Influence Extent of Coagulation in ex Vivo Bovine Livers?1

Christina Schraml, MD, Christophe Aubé, MD, Hansjoerg Graf, PhD, Andreas Boss, MD, Stephan Clasen, MD, Tina Herberts, PhD, Diethard Schmidt, MD, Fritz Schick, MD, PhD, Claus D. Claussen, MD and Philippe L. Pereira, MD

1 From the Department of Diagnostic Radiology, University Hospital of Tuebingen, Hoppe-Seyler-Str 3, 72076 Tuebingen, Germany. Received September 12, 2005; revision requested November 10; revision received December 23; accepted January 24, 2006; final version accepted March 20. Supported by Radionics Europe Valleylab. C.S. supported by the German Ministry for Education and Research (contract no. 16SV1351). Address correspondence to P.L.P. (e-mail: philippe.pereira{at}med.uni-tuebingen.de).

Purpose: To prospectively determine if static magnetic fields of magnetic resonance (MR) imagers affect radiofrequency (RF) ablation coagulation volume and shape.

Materials and Methods: Ex vivo RF ablations of bovine livers were performed with magnetic field strengths of 0.2, 1.5, and 3.0 T and were compared with ablations performed outside the magnetic field in a control group. Two MR-compatible monopolar RF devices (internally cooled single and cluster electrodes) were systematically tested. Length of long axis (y-axis), length of two short axes (x- and z-axes), and coagulation volume and shape measured outside and inside different magnetic fields were compared with the Dunnett test. Significance level was set to .05.

Results: For the single electrode, no significant difference was observed between length of short axes and coagulation volume and shape measured inside and outside the magnetic field. Mean x- and z-axis lengths were 2.3 and 2.6 cm, respectively, outside the magnetic field; 2.4 and 2.4 cm, respectively, at 0.2 T; 2.5 and 2.6 cm, respectively, at 1.5 T; and 2.2 and 2.5 cm, respectively, at 3.0 T. Differences between length of long axis, length of short axis perpendicular to static magnetic field, and coagulation volume and shape achieved with the cluster electrode inside and outside the magnetic field were not significant. Mean x- and z-axis lengths were 3.9 and 3.9 cm, respectively, outside the magnetic field; 3.7 and 3.8 cm, respectively, at 0.2 T; 4.0 and 4.3 cm, respectively, at 1.5 T; and 3.8 and 3.8 cm, respectively, at 3.0 T. Differences between ablations performed at 1.5 T and those performed in the control group with the cluster electrode were significant (P = .026). In this case, a difference of 4 mm in the length of the short axis parallel to the magnetic field was detected, but there was no significant difference in coagulation volume.

Conclusion: No significant differences in coagulation volume and shape could be recorded between RF ablations performed outside and those performed inside the static magnetic field.

© RSNA, 2006