MR-guided radiofrequency ablation: do magnetic fields influence extent of coagulation in ex vivo bovine livers?
OBJECTIVE
To prospectively determine if static magnetic fields of magnetic resonance (MR) imagers affect radiofrequency (RF) ablation coagulation volume and shape.


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.


CONCLUSIONS
No significant differences in coagulation volume and shape could be recorded between RF ablations performed outside and those performed inside the static magnetic field.
Schraml
Christina
C
Department of Diagnostic Radiology, University Hospital of Tuebingen, Hoppe-Seyler-Str 3, 72076 Tuebingen, Germany.
Aubé
Christophe
C
Graf
Hansjoerg
H
Boss
Andreas
A
Clasen
Stephan
S
Herberts
Tina
T
Schmidt
Diethard
D
Schick
Fritz
F
Claussen
Claus D
CD
Pereira
Philippe L
PL
D000818:Animals; D017115:Catheter Ablation; D002417:Cattle; D004566:Electrodes; D066298:In Vitro Techniques; D008099:Liver / Q000473:pathology*; D053783:Magnetic Resonance Imaging, Interventional / Q000379:methods*; D011446:Prospective Studies