High-intensity focused ultrasound (HIFU) has been studied for the purpose of developing a variety of medical therapies. Numerical and laboratory work has led to many clinical trials as well as first approved therapies, such as in the case of prostate cancer. However, little research has been performed to validate numerical simulations and in-vivo HIFU treatments in the presence of bones. To this end, recent advancements on visualization and optical measurements using schlieren techniques are presented in this work. In laboratory experiments, HIFU is induced in a tank filled with distilled water, and the incident waves are scattered at a bone phantom plate. Advanced filtering and computer vision techniques are adopted and their general feasibility is demonstrated for unobstructed and partially obstructed HIFU wave fields. In particular, it is shown that low-amplitude reflected wave peaks can be tracked despite their superposition with high-amplitude incident waves.
High-intensity focused ultrasound (HIFU) is currently being used for the ablation of tissue, such as in the case of prostate cancer. However, targeting tissue deeper inside the body remains challenging due to a variety of complications, including the increased scattering and attenuation of the ultrasonic waves. This work addresses the problem of exciting HIFU waves of a specific, desired wave form. That is, the utilized HIFU transducers are typically driven at their resonance frequency to maximize power output, which leads to significant distortions of the excited wave forms. In turn, these ringing effects can also have an impact on laboratory experiments as the resulting excess oscillations can obscure observations of visualization techniques, and in the clinic may cause unintended energy deposition at the target location. To mitigate this, an iterative learning control (ILC) approach is utilized with the intent of generating precise wave packets. Specifically, a PD-type and an H-infinity Synthesis approach are used to generate the ILC. It is shown that both ILCs lead to significant improvement of the excited pressure waves in simulation, i.e. the waveform more closely represents the desired tone burst. Furthermore, the model-based ILC design is shown to outperform the PD-type ILC, thus providing a systematic methodology. In addition to demonstrating its usefulness for developing new therapies through shadowgraph experiments, the methodology’s feasibility for future clinical use is discussed through an energy deposition analysis of more realistic wave forms for potential HIFU therapies.
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