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Super-heated sub-micrometre perfluorocarbon droplets have been shown to offer advantages over microbubbles for ultrasound localization microscopy (ULM). These include better penetration of the microcirculation and enabling higher frame rates using methods such as acoustic wave sparsely activated localization microscopy (AWSALM). The variability of droplet behaviour has however been found to be substantially higher than that of microbubbles and this poses challenges for ULM image construction. The aim of this study was to use simultaneous high speed optical and acoustic imaging to capture the droplet vaporisation process and subsequent bubble dynamics. Droplets composed of octofluoropropane and decafluorobutane were injected into a polyethylene tube submerged in a 37 °C water bath and located at the focus of an ultrasound probe and microscope objective. Optical images were captured at 10 Mfps of the droplet response to ultrasound pulses of varying lengths and amplitude. The results indicate that the number of activated droplets is impacted by increasing either the ultrasound pressure or number of half-cycles as well as by the preceding activation ultrasound pulses; and that different droplet sub-populations can be activated by varying pulse parameters. These data indicate the potential for optimising droplet activation of ULM applications.
Taylor et al. (Fri,) studied this question.