Liquid to gas phase transition of dye-loaded PFC nanodroplets (nanobombs, NBs) can be facilitated by the optical absorption of energy of laser pulse. Activation of NBs with laser pulse can produce highly localized longitudinal shear waves (LSW). The advent of LSW elastography has enhanced the ability to measure depth-dependent tissue elasticity. Highly localized NB-induced LSWs propagate through the tissue depth and can discriminate the tissue elasticity gradients along the depth. In this study, we explore the capability of the NB-induced LSWs in discriminating the elasticity properties of multilayered tissue-mimicking phantoms. The NB present in the middle layer of the test phantoms produced LSWs upon the pulse laser excitation, which can provide elasticity information in the sample depth where the NBs are located and the elasticity of layers of the sample on top and bottom of the NB layer.
Perfluorocarbon nanodroplets (PFCs) are a new class of liquid contrast agents that have been explored for ultrasound and photoacoustic imaging applications by the biomedical imaging community. These contrast agents can undergo a reversible or irreversible liquid-to-gas phase transitions upon an external excitation by a light or an ultrasound stimulus. Here, we evaluate the influence of apparently minute changes to the coating of PFCs and of dye-embedding strategies (i.e., for light activation) on the activation efficiency of the phase transition and the corresponding signal generation by PFCs. We discuss implications of these findings for further development of PFC contrast agents.
Current molecular imaging modalities face barriers to clinical implementation, providing a need for an improved clinical molecular imaging approach. We hypothesize that EGFR-targeted perfluorocarbon nanodroplets can label metastatic cells; they can then be activated (i.e., converted to a microbubble) and imaged using ultrasound in order to provide a molecular contrast agent that can inform treatment. Pulse sequences were developed for the Verasonics Vantage 128 system to activate and image dodecafluoropentane and dodecafluorohexane nanodroplets. Dodecafluoropentane nanodroplets provided 28-dB enhancement when imaged with pulse-inversion US in a tissue-mimicking environment, while dodecafluorohexane nanodroplets showed activation and subsequent recondensation, allowing for super-resolution imaging.
Wave-based optical coherence elastography (OCE) is a rapidly emerging technique for localized elasticity assessment of tissues due to its high displacement sensitivity and simple implementation. This method does not require prior knowledge of mechanical load characteristics, such as the applied preload and applied stress on the sample. Currently, noncontact wave excitation has been accomplished with various methods, such as focused micro air-pulse and acoustic techniques. However, they are limited by the inability to target specific tissues and usually only image the transversely propagating elastic wave, which generally requires scanning the probe beam across the sample. In addition, the upper frequency components of the elastic waves are limited to a few kilohertz, which are sensitive to boundary conditions due to their long wavelengths. In this study, we demonstrated that rapid vaporization of perfluorocarbon inside dye nanoparticles that was excited by a pulsed laser excitation, termed “nanobombs”, can produce high frequency longitudinal elastic waves in tissue mimicking phantoms. The nanoparticles were excited by a 1064 nm pulsed laser, which was co-focused with the OCT probe beam. The longitudinal elastic waves, which propagated axially (i.e., following the optical path), were directly imaged by a phase-sensitive Fourier domain mode-locked based OCT system. The detected elasticity was validated with well-established air-pulse OCE and the “gold standard” uniaxial mechanical testing. The results demonstrate the feasibility of performing nanobomb elastography in tissue with the potential for targeting specific tissues and producing longitudinal elastic waves with high frequency content.
Wave-based optical elastography is a rapidly emerging technique for viscoelastic assessment of tissues due to its high displacement sensitivity and simple implementation. This method does not require prior knowledge of mechanical load characteristics, such as the applied preload and applied stress on the sample. However, current truly noncontact excitation methods are limited by their inability to produce broadband waves with high frequency content. Lower frequency wave content is constrained by boundary conditions, and thus, requires specifically tailored mechanical models that consider the sample geometry. In this work, we demonstrate that rapid vaporization of perfluorocarbon inside dye nanoparticles (NP) with a pulsed laser can produce high frequency and broadband elastic waves in tissue mimicking agar phantoms. As a comparison, a focused air-pulse was used as an alternative excitation method. The elastic waves were imaged by an ultra-fast low-coherence line-field holography system. Our results show that the NPs produced elastic waves with frequencies up to ~9 kHz, while the air-pulse was only able to produce waves with frequency content up to ~2 kHz. The elastic wave dispersion curves were fitted to the analytical solution of a Rayleigh wave model to quantify viscoelasticity. Analysis of the broadband high-frequency waves produced by the NPs yielded more accurate quantification of the sample viscoelasticity, demonstrating the benefits of optically excited elastic waves.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.