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AJR 2005; 185:661-667
© American Roentgen Ray Society

Original Research

Radiofrequency Thermal Ablation in Canine Femur: Evaluation of Coagulation Necrosis Reproducibility and MRI-Histopathologic Correlation

Jeong Min Lee, Seong Hong Choi, Hee Seon Park, Min Woo Lee, Chang Jin Han, Joon-il Choi, Ja-Young Choi, Sung Hwan Hong, Joon Koo Han and Byung Ihn Choi

Department of Radiology and Institute of Radiation Medicine, Seoul National University College of Medicine, 28 Yongon-dong, Chono-gu, Seoul 110-744, South Korea.

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.

MATERIALS AND 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).

CONCLUSION. Radiofrequency ablation created well-defined coagulation necrosis in a reproducible manner, and MRI accurately determined the extent of the radiofrequency-induced thermal bone injury.


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