Comparative study of the dynamics of laser and acoustically generated bubbles in viscoelastic media

Abstract

Experimental observations of the growth and collapse of acoustically and laser-nucleated single bubbles in water and agarose gels of varying stiffness are presented. The maximum radii of generated bubbles decreased as the stiffness of the media increased for both nucleation modalities, but the maximum radii of laser-nucleated bubbles decreased more rapidly than acoustically nucleated bubbles as the gel stiffness increased. For water and low stiffness gels, the collapse times were well predicted by a Rayleigh cavity, but bubbles collapsed faster than predicted in the higher stiffness gels. The growth and collapse phases occurred symmetrically (in time) about the maximum radius in water but not in gels, where the duration of the growth phase decreased more than the collapse phase as gel stiffness increased. Numerical simulations of the bubble dynamics in viscoelastic media showed varying degrees of success in accurately predicting the observations.

Modeling tissue-selective cavitation damage

“…Simulations model a single, spherical, homobaric bubble in a homogenous viscoelastic medium exposed to a histotripsy waveform. Previous computational studies of histotripsy cavitation have used a similar model to study bubble dynamics in water (Vlaisavljevich et al 2016c) and agarose tissue phantoms (Vlaisavljevich et al 2014, 2015a, Vlaisavljevich et al 2016a, Mancia et al 2017, Wilson et al 2019). Table 1 lists viscoelastic and acoustic properties of each model tissue, and table 2 gives the constant initial conditions and thermodynamic properties used in all simulations.…”

Cavitation induced by shock wave focusing in eye-like experimental configurations

“…After reaching its maximum size, the bubble collapses, emits another shock wave, similar to the initial one, and the bubble grows again, this time to a smaller diameter [3]. A few bubble oscillations can be achieved, but the first two are always detectable [15].…”

High-speed photography of shock waves with an adaptive illumination

“…Due to light accumulation, more pulses make the shock wave less pronounced. A large portion of the bubble radius-versus-time curve can be easily extracted from a single figure, which is important in the studies of laser-and acoustically nucleated cavitation bubbles [12]. Likewise, the shock wave velocity as a function of distance from the emission origin can also be determined based on a single image [17].…”

“…An alternative approach is to modify the illumination part of the illumination-detection visualization system, while, if needed, preserving the benefits of fast-camera acquisition. This is a more affordable approach, because it is often sufficient to capture the object of interest, e.g., a shock wave [11] or a cavitation-bubble boundary [12], multiple times during a single exposure, where it is sufficient to use a simple still camera.…”

“…A drawback of using a typical laser source like Q-switched [13] or mode-locked lasers [11,14] as the light source is the inflexibility of the pulse modulation and the speckled, nonhomogeneous spatial profile. The illumination can be switched on and off relatively rapidly with LEDs [3,12,15], but to achieve high-brightness pulses with durations shorter than 100 ns, laser diodes are preferred, especially when unwanted light sources at other wavelengths have to be filtered out.…”