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High-intensity focused ultrasound (HIFU) is a noninvasive therapeutic application that focuses ultrasound to the target tissue, such as a malignant tumor, and thermally coagulates it. Monitoring methods for evaluating the formation of thermal lesions induced by HIFU are required to perform safe and accurate HIFU treatment. However, the conventional ultrasonic B-mode image incurs difficulties in assessing the formation of HIFU-induced lesions. In this study, ultrasound RF signals were acquired during HIFU exposure. A correlation coefficient was used to evaluate the changes occurring in the RF signals backscattered from the thermal lesion. Also, a block matching algorithm has been implemented to compensate the tissue motion during HIFU exposure. The experimental results show that correlation coefficients in the focal spot decreased significantly with HIFU exposure, which indicates that the backscattered RF signals changed owing to tissue coagulation.

Ultrasonic imaging has advantages in its self-consistency in guiding and monitoring ultrasonic treatment such as high-intensity focused ultrasound (HIFU) treatment. Changes in ultrasonic backscatter of tissues due to HIFU treatment have been observed, but their mechanism is still under discussion. In this paper, ultrasonic backscatter of excised and degassed porcine liver tissue was observed before and after HIFU exposure using a diagnostic scanner, and its acoustic impedance was mapped using an ultrasonic microscope. The histology of its pathological specimen was also observed using an optical microscope. The observed decrease in backscatter intensity due to HIFU exposure was consistent with a spatial Fourier analysis of the histology, which also showed changes due to the exposure. The observed increase in acoustic impedance due to the exposure was also consistent with the histological change assuming that the increase was primarily caused by the increase in the concentration of hepatic cells.

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This paper presents a novel erosion approach to reproduce fracture of concrete subjected to impact loadings. An erosion method is a numerical technique to remove highly distorted Lagrangian meshes which, if not deleted, tend to decrease the accuracy of numerical results obtained and often cause to terminate the calculation prematurely. Existing erosion criteria generally use a single thermo-mechanical variable for the deformation measure such as strain, stress tensor or damage. In this study we propose to utilize two measures to activate the erosion function with a view to better reproducing fracture zones of concrete by distinguishing the element deformation in compression or tension state. Test calculations in two and three dimensions are carried out to investigate the applicability of the proposed erosion method, and the numerical results are discussed with reference to available experimental data.