Acoustic and photoacoustic characterization of micron-sized perfluorocarbon emulsions

Abstract

Abstract. Perfluorocarbon droplets containing nanoparticles (NPs) have recently been investigated as theranostic and dual-mode contrast agents. These droplets can be vaporized via laser irradiation or used as photoacoustic contrast agents below the vaporization threshold. This study investigates the photoacoustic mechanism of NPloaded droplets using photoacoustic frequencies between 100 and 1000 MHz, where distinct spectral features are observed that are related to the droplet composition. The measured photoacoustic spectrum from NP-loaded perfluorocarbon droplets was compared to a theoretical model that assumes a homogenous liquid. Good agreement in the location of the spectral features was observed, which suggests the NPs act primarily as optical absorbers to induce thermal expansion of the droplet as a single homogenous object. The NP size and composition do not affect the photoacoustic spectrum; therefore, the photoacoustic signal can be maximized by optimizing the NP optical absorbing properties. To confirm the theoretical parameters in the model, photoacoustic, ultrasonic, and optical methods were used to estimate the droplet diameter. Photoacoustic and ultrasonic methods agreed to within 1.4%, while the optical measurement was 8.5% higher; this difference decreased with increasing droplet size. The small discrepancy may be attributed to the difficulty in observing the small droplets through the partially translucent phantom.

Photoacoustic measurements of single red blood cells

“…Previously our research group has shown that photoacoustic frequencies above 100 MHz can be used to identify and size spherically symmetric nanoparticle-loaded micron-sized perfluorocarbon droplets [15]. Periodically varying minima and maxima were observed throughout the power spectrum that are unique to the size, shape and composition of the object.…”

Photoacoustic Imaging in Oncology: Translational Preclinical and Early Clinical Experience

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