Visualization of HIFU-Induced Lesion Boundaries by Axial-Shear Strain Elastography: A Feasibility Study

Abstract

In this paper, we report on a study that investigated the feasibility of reliably visualizing high-intensity focused ultrasound (HIFU) lesion boundaries using axial-shear strain elastograms (ASSE). The HIFU-induced lesion cases used in the present work were selected from data acquired in a previous study. The samples consisted of excised canine livers with thermal lesions produced by a magnetic resonance–compatible HIFU system (GE Medical System, Milwaukee, WI, USA) and were cast in a gelatin block for the elastographic experiment. Both single and multiple HIFU-lesion samples were investigated. For each of the single-lesion samples, the lesion boundaries were determined independently from the axial strain elastogram (ASE) and ASSE at various iso-intensity contour thresholds (from –2 dB to –6 dB), and the area of the enclosed lesion was computed. For samples with multiple lesions, the corresponding ASSE was analyzed for identifying any unique axial-shear strain zones of interest. We further performed finite element modeling (FEM) of simple two-inclusion cases to verify whether the in vitro ASSE obtained were reasonable. The results show that the estimation of the lesion area using ASSE is less sensitive to iso-intensity threshold selection, making this method more robust compared with the ASE-based method. For multiple lesion cases, it was shown that ASSE enables high-contrast visualization of a “thin” untreated region in between multiple fully-treated HIFU-lesions. This contrast visualization was also noticed in the FEM predictions. In summary, the results demonstrate that it is feasible to reliably visualize HIFU lesion boundaries using ASSE. (E-mail: Arun.K.Thittai@uth.tmc.edu)