High-Intensity Ultrasound in Adherent Cell Sorting and Tissue Ablation

High-power ultrasound has been applied in many biomedical applications. However, many new applications and the associated challenges need to be addressed to advance high power ultrasound technology in medicine and biology. In this dissertation, the research objectives are: (1) to explore new high- intensity focused ultrasound (HIFU) applications in biology; (2) to enhance tissue ablation efficiency for more power efficient HIFU therapies. In order to achieve these objectives, several tasks were executed, and the background, design method and materials, experimental results and conclusions for each task were presented.;To explore new HIFU application in biology, the use of ultrasonic waves to release pallets for isolation of adherent live cells was investigated with high cell survivability. This technique has the potential for use in high-throughput cell sorting. This highly selective pallet/cell release method yields significantly higher cell viability after single-pallet release, comparing with other existing methods, largely resulting from the relatively slow release speed and low radiation forces.;To investigate more efficient HIFU therapies, a combined modeling and experimentation approach was employed to understand the physics behind the differences in tissue ablation behavior between single- and multi-frequency ultrasound. It is found that tissue ablation using multi-frequency HIFU yielded a up to 37.9 % higher temperature rise rate compared to ablation using single-frequency HIFU under the same exposure power and time. This finding has been verified by both thermocouple and MRI measurements, but cannot be explained well by the Pennes bio-heating theory, which does not consider cavitation. This more effective tissue ablation using multi-frequency HIFU is likely attributed to the enhanced cavitation effect based on the obtained cavitation detection results.;To investigate the cavitation effect under multi-frequency sonications, the enhanced effect of dual-frequency ultrasonic irradiation on cavitation yield was reported, for the first time, via the cavitation bubble modeling, followed by the cavitation yield characterization using the PCD (passive cavitation detection) method. Two-frequency (1.5 MHz/3 MHz) orthogonal pulse ultrasound was used in the tests. It was found that the simultaneous irradiation of dual frequency ultrasound can produce a significant increase in cavitation yield compared with single frequency irradiation. The possible mechanisms of the enhanced effect were briefly discussed and explained by the single-bubble cavitation model, where the calculated radiated pressure generated by acoustic bubble cavitation was found to be greater in dual-frequency cases.;Both the ultrasonic cell sorting study and the multi-frequency HIFU study suggest that high power ultrasound is promising for a broader range of applications in medicine and biology.