Cavitation, the linear or non-linear oscillation of bubbles under the effect of an ultrasound field, plays a key role in both non-invasive therapy and drug delivery by focused ultrasound. In 2007, we first developed a technique known as Passive Acoustic Mapping (PAM), which made it possible for the very first time to qualify and image cavitation activity in real-time at depth within the body. The technique relies on passive beamforming, whereby the location of cavitation sources are identified and imaged through weighed multi-correlations of acoustic emissions simultaneously received on the channels of a conventional high-frequency diagnostic ultrasound array.

[Image credit: Dr Calum Crake]

Since then, we have continuously developed this ubiquitous therapy monitoring method, with the aim of improving processing speed, enhancing spatial resolution and enabling its use as a quantitative metric of spatio-temporal cavitation activity that can serve as a surrogate and predictor of cavitation-mediated bioeffects. The application of PAM is today being explored as a means of real-time monitoring of cancer drug delivery, antimicrobial therapy by ultrasound, transdermal vaccine delivery and ultrasound-mediated immuno-modulation for oncological treatment. The technique has today translated into patients as part of the CEeDD (Cavitation-Enhanced Drug Delivery) clinical trial in partnership with OxSonics Therapeutics.