Spatially Localized Sono-Photoacoustic Activation of Phase-Change Contrast Agents

Abstract

Sono-photoacoustic (SPA) activation lowers the threshold of phase-change contrast agents by timing a laser shot to coincide with the arrival of an acoustic wave at a region of interest. The combination of photothermal heating from optical absorption and negative pressure from the acoustic wave greatly reduces the droplet’s combined vaporization threshold compared to using laser energy or acoustic energy alone. In previous studies, SPA imaging used a broadly illuminated optical pulse combined with plane wave acoustic pulses transmitted from a linear ultrasound array. Acoustic plane waves cover a wide lateral field of view, enabling direct visualization of the contrast agent distribution. In contrast, we demonstrate here that localized SPA activation is possible using electronically steered/focused ultrasound pulses. The focused SPA activation region is defined axially by the number of cycles in the acoustic pulse and laterally by the acoustic beam width. By reducing the spot size and enabling rapid electronic steering, complex activation patterns are possible, which may be particularly useful in therapeutic applications.

Acoustic Modulation Enables Proton Detection With Nanodroplets at Body Temperature

“…Thus, for in vivo range verification, a different approach to achieve direct vaporization of PFB nanodroplets by protons is preferred. In the context of sono-photoacoustic imaging, the simultaneous use of ultrasound and pulsed laser radiation was shown to facilitate the vaporization of nanodroplets coated with optical absorbers [39]- [41]. The vaporization threshold was reduced by the rarefactional phase of the acoustic wave compared to scenarios where ultrasound or pulsed laser illumination was used alone.…”

Repeated Acoustic Vaporization of Perfluorohexane Nanodroplets for Contrast-Enhanced Ultrasound Imaging

“…The benefits of repeatable activation come with the drawback of a higher activation threshold. Some groups have shown this threshold can be decreased through innovative strategies such as incorporating nucleation sites and multi-modal activation [55]- [57].In this study, activation is achieved with highamplitude, short pulses of HIFU. This waveform has a similar pulse duration to mechanical tissue disruption techniques, such as lithotripsy and histotripsy [58].…”

“…Alternatively, acoustic activation has a better depth of penetration and pulse repetition frequency. While the type of activation energy would probably be chosen based on the application, it is possible to image the same particles using both methods [55].…”

Multifunctional theragnostic ultrasmall gold nanodot-encapsuled perfluorocarbon nanodroplets for laser-focused ultrasound sequence irradiation (LFSI)-based enhanced tumor ablation

“…Liquid-gas phase transition-induced cavitation is believed to be the primary mechanism of enhanced FUS therapy with PFCnDs. [39][40][41][42] The cavitation threshold of Au-loaded PFCnDs was significantly reduced when ultrasound and laser radiation are applied simultaneously. [43][44][45] Here, the Au nanodots absorbed optical energy to trigger vaporization and serve as therapeutic agents for photothermal therapy (PTT).…”