Influence of the pulse repetition rate on the acoustic output of ballistic pressure wave devices

Ballistic devices that generate radial pressure waves are used for the treatment of different therapeutic indications. In order to assess the effectiveness of these devices and to interpret and transfer the results of clinical trials, it is important to know their acoustic output. In this paper, two ballistic devices and their reproducibility at different clinically relevant settings were investigated in the same in-vitro test setup. Pressure curves were measured in water at different intensity levels and pulse repetition rates. The sound field parameters (peak pressures, positive pulse intensity integral) were calculated from the pressure curves. Additionally, the surface velocity of the applicator was determined in air using a vibrometer. Both devices show a good pulse-to-pulse reproducibility. While the peak maximum pressure and the positive pulse intensity integral decrease only slightly (p(max) up to 12%, PII(+) up to 18.8%) comparing 1 Hz and 25 Hz for one device, they drop sharply (p(max) up to 68.4%, PII(+) up to 90.2%) for the other device comparing 1 Hz to 21 Hz. The same effect was observed in the vibrometer measurements. The results show that with increasing pulse repetition rate the stability of the parameters varies between different devices. Hence, all sound field parameters should be compared before transferring settings from one device to another.