Real time three-dimensional heat-induced echo-strain imaging for monitoring high-intensity acoustic ablation produced by conformal interstitial and external directional ultrasound therapy applicators

Abstract

Three dimensional heat-induced echo-strain imaging is a potentially useful tool for monitoring the formation of thermal lesions during ablative therapy. Heat-induced echo-strain, known as thermal strain, is due to the changes in the speed of propagating ultrasound signals and to tissue expansion during heat deposition. This paper presents a complete system for targeting and intraoperative monitoring of thermal ablation by high intensity focused acoustic applicators. A special software interface has been developed to enable motor motion control of 3D mechanical probes and rapid acquisition of 3D-RF data (ultrasound raw data after the beam-forming unit). Ex-vivo phantom and tissue studies were performed in a controlled laboratory environment. While B-mode ultrasound does not clearly identify the development of either necrotic lesions or the deposited thermal dose, the proposed 3D echo-strain imaging can visualize these changes, demonstrating agreement with temperature sensor readings and gross-pathology. Current results also demonstrate feasibility for real-time computation through a parallelized implementation for the algorithm used. Typically, 125 frames per volume can be processed in less than a second. Motion compensation can account for a shift within frames due to either tissue movement or positional error in the US 3D imaging probe.