Jingfeng Jiang, Presenter: Nothing to Disclose

Christopher L. Brace PhD, Abstract Co-Author: Shareholder, NeuWave Medical Inc, Madison, WI Consultant, NeuWave Medical Inc, Madison, WI

Ernest Louis Madsen PhD, Abstract Co-Author: Nothing to Disclose

Tomy Varghese, Abstract Co-Author: Nothing to Disclose

Timothy J. Hall PhD, Abstract Co-Author: Institutional research collaboration, Siemens AG Equipment support, Siemens AG Speaker, Siemens AG

Shyam Bharat MS, Abstract Co-Author: Nothing to Disclose

Maritza Hobson MS, Abstract Co-Author: Nothing to Disclose

James Anthony Zagzebski PhD, Abstract Co-Author: Researcher, General Electric Company Equipment support, Ultrasonix Medical Corporation

Fred T. Lee MD, Abstract Co-Author: Stockholder, NeuWave Medical Inc, Madison, WI Patent holder, Covidien AG, Boulder, CO

et al, Abstract Co-Author: Nothing to Disclose

Effective tumor localization and intra-procedural monitoring are critical to treatment success during thermal ablation. However, conventional B-mode ultrasound (US) per se is ineffective at depicting the margin of tissue coagulation. In this study, images of elastic modulus (E) were reconstructed using clinical US data to determine the size and the shape of the ablated area.

Ultrasound speckle tracking is used to measure tissue displacements after an induced compression. Elastic modulus (E) imaging is then achieved by iteratively adjusting local E values to enforce a mechanical model to produce displacements close to those measured. Validation studies were performed in TM phantoms and in vivo porcine livers. The phantom consisted of a simulated spherical (19-mm in diameter) ablated zone (elastic contrast = C = inclusion/background = 3.2) where a simulated irregularly-shaped liver tumor (C = 5.8) was embedded. Tissue Mimicking materials consist of dispersions of microscopic safflower oil droplets in an aqueous gelatin matrix. Stiffness values depend on the volume percentage of the oil. In animals, thermal lesions in the liver were created at thoracotomy using both radiofrequency and microwave applicators. In both experiments, radiofrequency ultrasound data was acquired under the guidance of a real-time strain imaging system. Ablation zones were excised and stained for viability to demarcate the zone of complete necrosis. Gross pathology images were digitally overlaid on E images to determine the overlap of in the imaged and ablated lesions.

In phantoms, the simulated ablated region was well correlated with that seen on the E image (>95% overlap). Ablated areas in liver as estimated from modulus reconstruction agreed with gross pathology (>90%). In one case, B-mode and strain images failed to accurately depict a bifurcated ablation zone while the E image was able to show the bifurcation accurately.

Elastic modulus imaging may be a more effective alternative to B-mode and strain imaging to determine true ablation zone boundaries.

Elastic modulus imaging has potential for improved localization of tumors and for monitoring tissue damage during and after thermal ablation treatments.

Jiang, J, Brace, C, Madsen, E, Varghese, T, Hall, T, Bharat, S, Hobson, M, Zagzebski, J, Lee, F, et al, , Thermal Ablation Monitoring: Elastic Modulus (E) Imaging Improves Visualization of Ablation Zones in Phantoms and in Vivo Animal Models.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6017782.html