Optimizing sonication protocols for transthoracic focused ultrasound surgery

During transthoracic focused ultrasound surgery (TFUS), the intervening ribs absorb and reflect the majority of the ultrasound energy excited by an acoustic source, resulting in pain, bone injuries and insufficient energy delivered to the target organs of liver, kidney, and pancreas. Localized hot spots may also exist at the interfaces between the ribs and soft tissue and in the highly absorptive regions such as the skin and connective tissue. The aims of this study were to clarify the effects of focal beam distortion and frequency-dependent rib heating in TFUS and to propose possible techniques to reduce the side-effects of rib heating and increase ultrasound efficacy. Frequency-dependent heating at the target and the ribs were estimated using finite element analysis (PZFlex, Weidlinger Associates Inc, USA) along with experimental verification on a range of different phantoms. The ratio of ultrasonic power density at the target and the ribs, the time-varying spatial distribution of temperature, and the a...