Monitoring boiling histotripsy with bubble-based ultrasound techniques

Abstract

Cavitation phenomena have been always considered as a predominant mechanism of concern in mechanical tissue damage induced by therapeutic ultrasound. Corresponding methods have been developed to monitor cavitation. Recently, a new high intensity focused ultrasound technology, called boiling histotripsy (BH), was introduced, in which the major physical phenomenon that initiates mechanical tissue damage is vapor bubble growth associated with rapid tissue heating to boiling temperatures. Caused by nonlinear propagation effects and the development of high-amplitude shocks, this tissue heating is localized in space and can lead to boiling within milliseconds. Once a boiling bubble is created, interaction of shock waves with the cavity results in tissue disintegration. While the incident shocks can lead to cavitation phenomena and accompanying broadband emissions, the presence of a millimeter-sized vapor cavity in tissue produces strong echogenicity in ultrasound (US) imaging that can be exploited with B-mode diagnostic ultrasound. Various other methods of imaging boiling histotripsy, including passive cavitation detection (PCD), Doppler or nonlinear pulse-inversion techniques, and high speed photography in transparent gel phantoms are also overviewed. The role of shock amplitude as a metric for mechanical tissue damage is discussed. [Work supported by NIH EB007643, T32DK007779, and NSBRI through NASA NCC 9-58.]