Laser-driven resonance of dye-doped oil-coated microbubbles: A theoretical and numerical study

Abstract

Microbubbles are used to enhance the contrast in ultrasound imaging. When coated with an optically absorbing material, these bubbles can also provide contrast in photoacoustic imaging. This multimodal aspect is of pronounced interest to the field of medical imaging. The aim of this paper is to provide a theoretical framework to describe the physical phenomena underlying the photoacoustic response. This article presents a model for a spherical gas microbubble suspended in an aqueous environment and coated with an oil layer containing an optically absorbing dye. The model includes heat transfer between the gas core and the surrounding liquids. This framework is suitable for the investigation of both continuous wave and pulsed laser excitation. This work utilizes a combination of finite difference simulations and numerical integration to determine the dependancy on the physical properties, including composition and thickness of the oil layer on the microbubble response. A normalization scheme for a linearized version of the model was derived to facilitate comparison with experimental measurements. The results show that viscosity and thickness of the oil layer determine whether or not microbubble resonance can be excited. This work also examines the use of non-sinusoidal excitation to promote harmonic imaging techniques to further improve the imaging sensitivity.

Brandaris Ultra High-Speed Imaging Facility

“…The middle section shows the R − t curve of the two sets of bubbles and clearly displays the expansion and contraction at the eigenfrequency of the system, which can be used to fully characterize the system. More details of these experiments can be found in [28,29] and details are also found in Chap. 9 (Stride et al).…”

Laser-activated microparticles for multimodal imaging: ultrasound and photoacoustics

“…Such improvement, however, is made at the cost of a much reduced penetration depth, typically limited to 1 cm (Mallidi et al 2011). Here as well, contrast agents have been developed to address the penetration issue, and these include dyes (Kim et al 2007, Bhattacharyya et al 2008, Stantz et al 2010, nanoparticles (Li et al 2006, Mallidi et al 2009, Bayer et al 2011, microbubbles with dyed coatings (Jeon et al 2014, Lajoinie et al 2017a, 2017b, polymeric microcapsules (Lajoinie et al 2014, Yue et al 2017 and microdroplets (Wilson et al 2010). These agents improve contrast by either absorbing light at a more favorable wavelength, within the tissue optical window, or by presenting an order of magnitude stronger absorption than native chromophores (Luke et al 2012).…”