Passive acoustic mapping of cavitation during shock wave lithotripsy

Abstract

Passive acoustic mapping (PAM) has previously been used to localize inertial cavitation during high intensity focused ultrasound. Here, this technique has been applied to shock wave lithotripsy (SWL), a non-invasive procedure whereby kidney stones are fragmented. Conventional diagnostic ultrasound probes were used to detect acoustic emissions during SWL. Signals consisted of reverberation sound from the incident shock wave followed, several hundred microseconds later, by emissions from cavitation collapses. Time-gating was used to isolate the cavitation signals, which were then processed using PAM to create spatial maps of the cavitation activity. Experiments in water indicated the spatial resolution was an ellipsoidal volume 5mm long by 1mm wide. Experiments were carried out in ex vivo pig kidneys and it was observed that cavitation was initiated in the region of the focus but moved laterally by up to 10mm and during treatment exhibited a general migration towards the source. These results suggest that P...