Investigation on the comparability of the light spot hydrophone and the fiber optic hydrophone in lithotripter field measurements

Abstract

Optical hydrophones are optimized pressure-pulse-sensors used for high-power shockwave sources, such as lithotripters. Recent investigation of Smith et al. ["A Comparison of light spot hydrophone and fiber optic probe hydrophone for lithotripter field characterization," Rev. Sci. Instrum. 83, 014301 (2012)] show discrepancies in the negative pressure peak and tensile pulse duration regarding measurements carried out with two optical hydrophones: the Light Spot Hydrophone (LSHD) and the fiber optic hydro-phone. It was assumed that the differences arise from cavitation effects at the end-face of the LSHD glass-block and filter characteristics of the trans-impedance amplifier of the LSHD. The present study investigates the transfer-function of the LSHD. It is shown that the filter characteristics of the amplifier cause discrepancies in the rarefaction pressure pulse fraction (depending on the energy settings of the source 15 ± 2%).

Review of field characterization techniques for high intensity therapeutic ultrasound

“…Depending on the configuration of the optical resonator, the ultrasound field can be characterized such that either the acoustic axis is parallel or perpendicular to the optical beam. The most frequently used are classic FP interferometers [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55] and fiber Bragg gratings (FBGs) [56][57][58].…”

“…These characteristics favor the use of a system as a reference hydrophone for secondary calibrations using pulse excitation [47,50]. Different versions of the sensor with larger substrates were also developed using the Fresnel reflection type for photoacoustic imaging [52] and for lithotripter shock-wave measurement [31,53], as well as using the parylene spacer, FP interferometers [54]. However, it is difficult to apply these sensors to HITU measurements, which comprise of relatively long waveforms or bursts, due to the limited measurement time window.…”