Acoustic detection of controlled laser-induced microbubble creation in gelatin

Abstract

A high-frequency (85 MHz) acoustic technique is used to identify system parameters for controlled laser-induced microbubble creation inside tissue-mimicking, gelatin phantoms. Microbubbles are generated at the focus of an ultrafast 793-nm laser source and simultaneously monitored through ultrasonic pulse-echo recordings. Displayed in wavefield form, these recordings illustrate microbubble creation, and integrated backscatter plots provide specifics about microbubble characteristics and dissolution behavior. By varying laser parameters, including pulse fluence (or pulse energy flux, J/cm 2 ), total number of pulses delivered, and the period between pulses, the size, lifetime, and dissolution dynamics of laser-induced microbubbles may be independently controlled. Pulse fluence is the main sizecontrolling parameter, whereas both increases in pulse fluence and pulse number can lengthen microbubble lifetime from tens to hundreds of milliseconds. In short, a microbubble of particular lifetime does not necessarily have to be of a particular size. Microbubble behavior, furthermore, is independent of pulse periods below a fluence-dependent threshold value, but it exhibits stochastic behavior if pulse repetition is too slow. These results demonstrate that laser pulse fluence, number, and period may be varied to deposit energy in a specific temporal manner, creating and stabilizing microbubbles with particular characteristics and, therefore, potential uses in sensitive acoustic detection and manipulation schemes.

Mapping age-related elasticity changes in porcine lenses using bubble-based acoustic radiation force

“…Optical parameters such as laser pulse number and pulse fluence can be used to control bubble size and lifetime (Tse et al, 2005). Previous in vitro measurements using bright-field transmission microscopy show maximum bubble diameters in the range of 30 -100 μm in porcine lenses using similar optical parameters as the present study (Erpelding et al, 2005b).…”

Enhanced optical breakdown in KB cells labeled with folate-targeted silver-dendrimer composite nanodevices

“…Although absolute bubble size was not quantified from bubble backscatter data, we estimated a 3.2 to 6.2 μM diameter range (corresponding to a −65 to −60 dB backscatter range) from backscatter measurements from a range of polystyrene beads of known sizes [34]. …”

“…Breakdown threshold for CNDs was defined as the lowest fluence that generated laser-induced bubbles acoustically detectable via a previously reported high-frequency technique [25, 34]. Breakdown threshold is determined for each sample by monitoring bubble activity at variable average laser powers and evaluating maximum integrated backscatter (defined as the backscattered acoustic power from the bubble normalized to the power recorded for a perfect planar reflector using precisely the same transducer and electronics).…”

“…High frequency ultrasound monitors generation, fate, and collapse of microbubbles and could characterize LIOB by detecting its mechanical effects, including acoustic radiation and pulse-echo signals from resulting microbubbles. Successive recordings displayed in a wavefield form provided an “image” of breakdown dynamics [20, 25, 34]. …”

Subsurface photodisruption in pig skin as monitored by high-frequency ultrasound

“…As acoustic emissions produced by LIOB and resultant microbubbles are easily detectable ultrasonically, high-frequency ultrasound operating over a few mm propagation path through tissue is a sensitive, high resolution technique to monitor breakdown. 9 We varied optical parameters including laser fluence, optical propagation path length through the skin samples, and focusing lens numerical aperture.…”