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© 2008 by the American Institute of Ultrasound in Medicine
J Ultrasound Med 27:935-946 • 0278-4297

Technical Advance

Ultrasound-Based Elastography: A Novel Approach to Assess Radio Frequency Ablation of Liver Masses Performed With Expandable Ablation Probes

A Feasibility Study

Orpheus Kolokythas, MD, Thomas Gauthier, MS, Anna T. Fernandez, PhD, Hua Xie, PhD, Brian A. Timm, RDMS, Carlos Cuevas, MD, Manjiri K. Dighe, MD, Lee M. Mitsumori, MD, Matt F. Bruce, PhD, Daniel A. Herzka, PhD, Gaurav K. Goswami, MD, R. Torrance Andrews, MD, Kelly M. Oas, RDMS, Theodore J. Dubinsky, MD and Bill H. Warren, MD

Department of Radiology, University of Washington Medical Center, Seattle, Washington USA (O.K., B.A.T., C.C., M.K.D., L.M.M., G.K.G., R.T.A., K.M.O., T.J.D., B.H.W.); Philips Medical Systems, Bothell, Washington USA (T.G., M.F.B.); and Philips Research North America, Briarcliff Manor, New York USA (A.T.F., H.X., D.A.H.).

Address correspondence to Orpheus Kolokythas, MD, Department of Radiology, University of Washington, 1959 NE Pacific St, BB-308 HSC, Box 357115, Seattle, WA 98195-7115 USA. E-mail: orpheus{at}u.washington.edu

Objective. The purpose of this study was to evaluate the technical feasibility of ultrasound-based elastography as a tool for assessing the size and shape of the coagulation necrosis caused by radio frequency ablation (RFA) probes using expandable electrodes ex vivo as well as in a patient with a liver metastasis. Methods. A commercially available expandable RFA probe was used to create a 3-cm ablation in a piece of bovine liver. The ablation probe was used in situ to induce tissue deformation for elastography before and after ablation. Ultrasonic radio frequency data were processed to generate elasticity strain images. The appearance of the ablation zone was compared with magnetic resonance imaging and a gross section specimen. One patient with malignant metastatic disease to the liver and a clinical indication for RFA was investigated for the feasibility of percutaneous elastography of RFA using the same technique. Sonographic strain images were compared with the appearance of the nonenhancing ablation zone on contrast-enhanced computed tomography. Results. Ex vivo, the ablation zone on ultrasound-based elastography was represented by an area of increased stiffness and was well demarcated from the nonablated surrounding tissue. The size and shape of the ablated zone on the strain image correlated well with the gross specimen and the magnetic resonance imaging appearance. Strain images obtained from the patient showed results similar to those of the ex vivo experiment and correlated well with the nonenhancing area of ablation on contrast-enhanced computed tomography. Conclusions. Ultrasound-based elastography may be a promising tool for displaying the ablation zone created by expandable RFA probes.

Key Words: elasticity imaging • elastography • radio frequency ablation • strain imaging • ultrasound

Abbreviations: CT, computed tomography • MR, magnetic resonance • MRI, magnetic resonance imaging • PET, positron emission tomography • RF, radio frequency • RFA, radio frequency ablation • 2D, 2-dimensional

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Copyright © 2008 by the American Institute of Ultrasound in Medicine.