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Femur: MR Imaging–guided Radio-frequency Ablation in a Porcine Model— Feasibility Study¹

¹ From the Departments of Radiology (A.J.A., E.M.M., C.A.P., J.L.D., J.S.L.), Pathology (S.N.E.), and Oncology (J.S.L.), University Hospitals of Cleveland/Case Western Reserve University, 11100 Euclid Ave, Cleveland, OH 44106; Department of Diagnostic Radiology, University Hospital of Ulm, Germany (A.J.A., E.M.M.); and Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio (J.L.D.). From the 2000 RSNA scientific assembly. Received September 6, 2000; revision requested October 20; final revision received May 7, 2002; accepted May 29. Supported in part by grants from the Whitaker Foundation, American Cancer Society, National Institutes of Health (1R01 CA81431-01A1), and the German Research Foundation (DFG, As 116/1-1 and Me 1593/1-1), and by research collaborations with Siemens Medical Systems and Radionics. Address correspondence to J.S.L. (e-mail: lewin@uhrad.com).

PURPOSE: To determine the feasibility of magnetic resonance (MR) imaging–guided and –monitored radio-frequency (RF) ablation of bone.

MATERIALS AND METHODS: Seven femurs were treated in five pigs with use of a 0.2-T open MR imager. An 11-gauge bone marrow needle was percutaneously inserted into the distal femur metaphysis with MR fluoroscopy (fast imaging with steady-state precession, or FISP, sequences) to introduce an RF electrode into the bone with further image guidance. Thermal ablation was performed for 10 minutes (90°C ± 2 [mean ± SD]). MR follow-up was performed immediately after ablation and again at 7 and 14 days after the procedure (with contrast material–enhanced T1-weighted, T2-weighted, and fast short inversion time inversion-recovery, or STIR, sequences). The animals were sacrificed at day 14. The femurs were sliced, decalcified, and stained. Image analysis was performed to measure lesion diameter and contrast-to-noise ratio (CNR) and to evaluate complications.

RESULTS: Technical success was obtained in all animals. The lesion diameter perpendicular to the electrode was 15.4 mm ± 2.7. No significant complications were noted. The thermal lesions displayed low signal intensity with a sharp rim of high signal intensity. T2-weighted images demonstrated the highest CNR and the lowest error in predicting the lesion size immediately after ablation (2.7 mm ± 1.3). Contrast-enhanced T1-weighted images demonstrated the highest accuracy at day 14 (1.0 mm ± 1.0).

CONCLUSION: RF ablation of bone with MR imaging as the sole imaging modality is feasible and allows monitoring of the ablation.

© RSNA, 2002

Index terms: Animals • Femur, MR, 445.121411, 445.121412, 445.121413 • Femur, neoplasms, 445.3122, 445.33 • Magnetic resonance (MR), guidance, 445.121411, 445.121412, 445.121413 • Radiofrequency (RF) ablation, 445.1299

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