High-intensity focused ultrasound (HIFU) has demonstrated the capacity to be used for local thermal ablation in clinical surgery; however, relying solely on conventional ultrasound B-mode imaging to monitor HIFU thermal ablation and determine ablation levels remains a challenge. Here, we experimentally demonstrate the ability to use Nakagami imaging to monitor HIFU-induced thermal lesions in porcine livers ex vivo. Ultrasonic Nakagami imaging has been proven to be able to characterize tissues with different scatterer concentrations and distributions. The pathological sections from HIFU thermally ablated porcine liver tissues reveal that normal and denatured tissues significantly differ in scatterer concentration and distribution. Therefore, we believe that Nakagami imaging can be used to monitor thermal ablation by tracing Nakagami parameter changes in liver tissues. The ex vivo porcine liver experiments were performed using a homemade HIFU device synchronized with a commercial diagnostic ultrasound scanner to obtain the ultrasound envelope data before and after thermal ablation. These data were used to evaluate the performance of thermal lesion characterization using Nakagami imaging and were compared with those derived from conventional B-mode imaging. Experimental results showed that Nakagami imaging can be used to identify thermal lesions, which are difficult to visualize using conventional B-mode imaging because there is no apparent bubble formation. In cases with apparent bubble formation, Nakagami imaging could provide a more accurate estimation of lesion size and position. In addition, the Nakagami imaging algorithm is characterized by low computational complexity, which means it can be easily integrated as postprocessing for existing array imaging systems.

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The traditional small-scale marine engineering experiments that are performed under normal gravity fields always encounter one stubborn difficulty related to full-scale prototype models. However, the difficulty can be resolved by centrifuge experiments that can generate hypergravity fields in which the centrifuge acceleration is many times greater than the gravity acceleration. In this study, the generation of solitary waves in hypergravity fields is proposed using solitary wavemaker theory and scaling laws. A series of case simulations are performed under four different gravity fields (1 g, 30 g, 50 g, and 100 g, where g is the gravity acceleration). These cases are presented and discussed in detail to understand and verify the scaling laws and the stability of the solitary wave during its generation and propagation within hypergravity fields. The numerical results show that the waveform and the static pressure field that are obtained during the simulations performed under different gravity fields agree well at the macroscale. Since the velocity field is sensitive to wave attenuation, time lag, fluid viscosity and surface tension, some discrepancies can be found in the velocity field. It should be noted that the fluid viscosity and surface tension have influence on the wave attenuation. However, wave attenuation and time lag can be offset by a well-designed incident wave condition.

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