Control of cavitation activity by different shockwave pulsing regimes

The aim of the study was to control the number of inertial cavitation bubbl es in the focal area of an electromagnetic lithotripter in water independen tly of peak intensity, averaged intensity or pressure waveform. To achieve this, the shockwave pulses were applied in double pulse sequences, which we re administered at a fixed pulse repetition frequency (PRF) of 0.33 Hz. The two pulses of a double pulse were separated by a variable short pulse sepa ration time (PST) ranging from 200 mu s to 1500 ms. The number and size of the cavitation bubbles were monitored by scattered laser light and strobosc opic photographs. We found that the number of inertial cavitation bubbles a s a measure of cavitation dose was substantially influenced by variation of the PST, while the pressure pulse waveform, averaged acoustic intensity an d bubble size were kept constant. The second pulse of each double pulse gen erated more cavitation bubbles than the first. At 14 kV capacitor voltage, the total number of cavitation bubbles generated by the double pulses incre ased with shorter PST down to approximately 400 mu s, the cavitation lifesp an. The results can be explained by cavitation nuclei generated by the viol ently imploding inertial cavitation bubbles. This method of pulse administr ation and cavitation monitoring could be useful to establish a cavitation d ose-effect relationship independently of other acoustic parameters.