Radiofrequency thermal ablation in canine femur: evaluation of coagulation necrosis reproducibility and MRI-histopathologic correlation.
OBJECTIVE
Our purposes were to determine whether a single application of radiofrequency energy to normal bone can create coagulation necrosis reproducibly and to assess the accuracy of MRI at revealing the extent of radiofrequency-induced thermal bone injury.


METHODS
Using a 200-W generator and a 17-gauge cooled-tip electrode, a total of 11 radiofrequency ablations were performed under fluoroscopic guidance in the distal femurs of seven dogs. Radiofrequency was applied in standard monopolar mode at 100 W for 10 min. During radiofrequency ablation, the changes in impedance and currents were recorded. MRI, including unenhanced T1- and T2-weighted images and contrast-enhanced fat-suppressed T1-weighted images, was performed to evaluate ablation regions. Six dogs were killed on day 4 after MRI and one dog on day 7.


RESULTS
In all animals, radiofrequency ablation created a well-defined coagulation necrosis and no significant complications were noted. The mean long-axis diameter and the mean short-axis diameter of the coagulation zones produced were 45.9 +/- 5.5 mm and 17.7 +/- 2.7 mm, respectively. At gross examination, thermal ablation regions appeared as a central, light-brown area with a dark-brown peripheral hemorrhagic zone, which was surrounded by a pale-yellow rim. On MRI, the ablated areas showed multilayered zones with signal intensities that differed from normal marrow on unenhanced images and a perfusion defect on contrast-enhanced T1-weighted images. The maximum difference between lesion sizes on MR images, established by measuring macroscopic coagulation necrosis, was 3 mm. The correlation between the diameter of coagulation necrosis and lesion size at MRI was strong, with correlation coefficients ranging from 0.89 for unenhanced T1-weighted images and 0.97 for unenhanced T2-weighted images to 0.98 for contrast-enhanced T1-weighted images (p < 0.05).


CONCLUSIONS
Radiofrequency ablation created well-defined coagulation necrosis in a reproducible manner, and MRI accurately determined the extent of the radiofrequency-induced thermal bone injury.
Lee
Jeong Min
JM
Department of Radiology, Seoul National University College of Medicine, Chono-gu, Seoul 110-744, South Korea.
Choi
Seong Hong
SH
Park
Hee Seon
HS
Lee
Min Woo
MW
Han
Chang Jin
CJ
Choi
Joon-il
JI
Choi
Ja-Young
JY
Hong
Sung Hwan
SH
Han
Joon Koo
JK
Choi
Byung Ihn
BI
D000818:Animals; D017115:Catheter Ablation; D004285:Dogs; D005260:Female; D005269:Femur / Q000293:injuries* / Q000601:surgery*; D005471:Fluoroscopy; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009336:Necrosis; D015203:Reproducibility of Results