Photoacoustic imaging: contributions to optical-resolution photoacoustic endoscopy and experimental investigation of thermal nonlinearity

Abstract : Photoacoustic imaging is a new hybrid imaging technique that provides images of optical absorption at centimeters depth in biological tissues with the resolution of ultrasound. Exogenous contrast agents such as gold nanoparticles can also be used to enhance image contrast and image disease-specific receptors. However, there is a trade-off between resolution and imaging depth. Moreover, specific detection of exogenous contrast agents often requires the use of multispectral imaging which can be challenging because of the complex propagation of light in biological tissues. This thesis presents a new approach to micron-scale optical-resolution photoacoustic microscopy (OR-PAM) at centimeters depth based on a minimally-invasive endoscope, and experimentally investigates the possibility of improving gold nanospheres detection based on thermal nonlinear photoacoustic generation. It is first shown that OR-PAM images can be generated at the distal tip of a multimode fiber by use of digital phase conjugation. It is then shown that OR-PAM images can be transmitted through tissue in a silica-capillary acoustic waveguide for remote detection at the tissue surface. Preliminary experiments suggest that the two previous approaches could be combined in a setup based on a unique silica capillary acting both as an optical and an acoustic waveguide to acquire OR-PAM images at centimeters depth in tissues. Finally, it is shown that organic-dye and gold-nanospheres aqueous solutions can be discriminated thanks to thermal nonlinearity, based on the dependence of the photoacoustic amplitude with fluence or temperature.
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Submitted on : Friday, February 27, 2015 - 2:44:48 PM
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  • HAL Id : tel-01121119, version 1

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Olivier Simandoux. Photoacoustic imaging: contributions to optical-resolution photoacoustic endoscopy and experimental investigation of thermal nonlinearity. Physics [physics]. Université Paris Diderot Paris 7, 2015. English. ⟨tel-01121119⟩

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