Abstract
Laser-activated perfluorocarbon nanodroplets (PFCnDs) are emerging phase-change contrast agents that showed promising potential in ultrasound and photoacoustic (US/PA) imaging. Unlike monophase gaseous microbubbles, PFCnDs shift their state from liquid to gas via optical activation and can provide high US/PA contrast on demand. Depending on the choice of perfluorocarbon core, the vaporization and condensation dynamics of the PFCnDs are controllable. Therefore, these configurable properties of activation and deactivation of PFCnDs are employed to enable various imaging approaches, including contrast-enhanced imaging and super-resolution imaging. In addition, synchronous application of both acoustic and optical pulses showed a promising outcome vaporizing PFCnDs with lower activation thresholds. Furthermore, due to their sub-micrometer size, PFCnDs can be used for molecular imaging of extravascular tissue. PFCnDs can also be an effective therapeutic tool. As PFCnDs can carry therapeutic drugs or other particles, they can be used for drug delivery, as well as photothermal and photodynamic therapies. Blood barrier opening for neurological applications was recently demonstrated with optically-triggered PFCnDs. This paper specifically focuses on the activation and deactivation properties of laser-activated PFCnDs and associated US/PA imaging approaches, and briefly discusses their theranostic potential and future directions.
Highlights
Over the past decade, phase-change contrast agents were rigorously studied and showed promising outcomes in diagnostic ultrasound imaging and therapeutic applications [1,2,3,4,5,6]
Phase-change contrast agents were rigorously studied and showed promising outcomes in diagnostic ultrasound imaging and therapeutic applications [1,2,3,4,5,6]. These contrast agents consisting of a liquid perfluorocarbon (PFC) core, referred to as perfluorocarbon nanodroplets (PFCnDs), undergo a phase transition from liquid to gaseous state in response to an external trigger [7,8]
Image-guided delivery of therapeutics using PFCnDs recently showed that PFCnDs have a capacity for simultaneous drug delivery and ultrasound monitoring, indicating that localized treatment and imaging of cancer with PFCnDs may be feasible in the future [50]
Summary
Phase-change contrast agents were rigorously studied and showed promising outcomes in diagnostic ultrasound imaging and therapeutic applications [1,2,3,4,5,6] These contrast agents consisting of a liquid perfluorocarbon (PFC) core, referred to as perfluorocarbon nanodroplets (PFCnDs), undergo a phase transition from liquid to gaseous state in response to an external trigger [7,8]. They can vaporize and recondense, which provides repeatable high US/PA contrast over a course of laser irradiation. Repeatable volumetric expansion makes this agent photoacoustically attractive, as high-contrast photoacoustic signals can be produced from the vaporization event This unique, repeated phase-changing property of high-boiling-point PFCnDs showed promising capabilities in US/PA imaging and therapeutic applications, including contrastenhanced imaging, super-resolution imaging, extravascular tumor imaging, blood-brain barrier opening, and more. Last section briefly summarizes diagnostic and therapeutic trends for applications
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