Lithotripsy pulse measurement errors due to nonideal hydrophone and amplifier frequency responses.

When using miniature ultrasonic hydrophones to probe the focal region of extracorporeal shock wave lithotripsy devices, the frequency response of the measurement hydrophone and any associated amplifier must be broad enough to minimize pulse distortion. To study the potential effects of the bandwidth-limited behavior, a mathematical model was used. Several parameters of a simulated lithotripsy pulse were compared before and after being filtered by hydrophone and amplifier response functions. Errors were computed for the peak positive and negative pressures, risetime, pulse duration, and pulse intensity integral as functions of hydrophone and amplifier bandwidths. Although most of the energy in a shock wave pulse lies at frequencies below a few megahertz, it is found that significant errors can occur unless measurement bandwidths are much wider.