VISUALIZATION OF HIFU-INDUCED LESION BOUNDARIES BY AXIAL-SHEAR STRAIN ELASTOGRAPHY: A FEASIBILITY STUDY

摘要

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 an MR-compatible HIFU system (GE Medical System, Milwaukee, WI) and were cast in a gelatin block for elastographic experiment. Both single and multiple HIFU-lesion samples were investigated. For each of the single lesion sample, the lesion boundaries were determined independently from the axial strain elastogram (ASE) and ASSE at various iso-intensity contour thresholds (from −2dB to −6dB), 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 if 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 to ASE-based method. For multiple lesion case, 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.