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.
Chih-Hao Liu, Alexander Schill, Susobhan Das, Dmitry Nevozhay, Manmohan Singh, Achuth Nair, Konstantin V. Sokolov, and Kirill Larin, "Optical elastography using dye nanoparticles (Conference Presentation)," Proc. SPIE 10496, Optical Elastography and Tissue Biomechanics V, 1049605 (Presented at SPIE BiOS: January 27, 2018; Published: 15 March 2018); https://doi.org/10.1117/12.2290886.5752215489001.
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