Abstract
Nanodroplets have emerged as promising contrast agents due to their ability to undergo acoustic droplet vaporization (ADV), enabling size expansion for diverse biological applications such as selective contrast enhancement and localized drug delivery. While ADV has been widely utilized, the influence of acoustic parameters on its dynamics remains poorly understood, despite their potential to modulate ADV efficiency and uniformity, particularly with focused ultrasound (FUS). In this study, we developed a well-defined synthetic and characterization protocol for anionic perfluoropentane (PFP) nanodroplets and systematically investigated the effects of the pulse repetition frequency (PRF) and cycle number on ADV using acoustic signal detection and B-mode ultrasound imaging. In addition, we developed a modified acoustic-thermal model and simulation framework to elucidate the underlying mechanisms governing ADV behavior. Our findings reveal that increasing PRF and cycle number independently lowers ADV thresholds until reaching a saturation point, indicating that excessive ultrasound intensity is unnecessary. The acoustic conditions (PRF = 1000 Hz; cycle number = 175) were successfully applied in vivo, yielding substantial brightness enhancement at both low (0.129) and high (1.4) imaging mechanical indices (MIs), with improved parenchyma (1.86-fold) and vascular (2.21-fold) visualization. This study underscores the critical role of acoustic parameters in achieving precise and controlled ADV, paving the way for nanodroplet-based theranostics in clinical applications.