An ultrasound-based technique capable of detection and
spatio-temporal characterization of microbubbles induced in
water by femtosecond laser is reported. A highly focused
single-element ultrasound transducer was used both to detect
passive acoustic emission of the microbubbles and to probe the microbubbles at different stage of their evolution. The
location of origin and wall of the microbubble was assessed from temporal characteristics of the passive acoustic
emissions and of the pulse-echo signals. The radius of the microbubble was estimated as the distance between the origin
of the bubble and its wall. The ultrasound characterization of microbubbles induced by femtosecond pulses agreed well
with theoretical predictions based on the well-known Rayleigh-based model of bubble behavior in liquid. The results of
this study demonstrate that femtosecond laser-induced microbubbles with typical sizes of several tens of micrometers
can be characterized by the developed ultrasound technique.
An ultrasound technique to measure the spatial and temporal behavior of the laser-induced cavitation bubble is introduced. The cavitation bubbles were formed in water and in gels using a nanosecond pulsed Nd:YAG laser operating at 532 nm. A focused, single-element, 25-MHz ultrasound transducer was employed both to detect the acoustic emission generated by plasma expansion and to acoustically probe the bubble at different stages of its evolution. The arrival time of the passive acoustic emission was used to estimate the location of the cavitation bubble's origin and the time of flight of the ultrasound pulse-echo signal was used to define its spatial extent. The results of ultrasound estimations of the bubble size were compared and found to be in agreement with both the direct optical measurements of the stationary bubble and the theoretical estimates of bubble dynamics derived from the well-known Rayleigh model of a cavity collapse. The results of this study indicate that the proposed quantitative ultrasound technique, capable of detecting and accurately measuring laser-induced cavitation bubbles in water and in a tissue-like medium, could be used in various biomedical and clinical applications.
An ultrasound-based method to detect and characterize the laser-induced microbubbles was developed. This method is based on temporal measurement of passive acoustic emission from cavity during laser-tissue interaction and simultaneous active pulse-echo ultrasound probing of the cavitation bubble. These measurements were used to estimate the location of the nanosecond laser induced cavity and to monitor the spatial and temporal behavior of the microbubble. The measurements agreed with estimates derived from a well-known Rayleigh model of the cavity collapse. Overall, the studies indicate that the developed ultrasound technique can be used to detect and accurately measure laser-induced microbubbles in tissue.