Optical-resolution photoacoustic imaging through thick tissue with a thin capillary as a dual optical-in acoustic-out waveguide

We demonstrate the ability to guide high-frequency photoacoustic waves through thick tissue with a water-filled silica-capillary (150 \mu m inner diameter and 30 mm long). An optical-resolution photoacoustic image of a 30 \mu m diameter absorbing nylon thread was obtained by guiding the acoustic waves in the capillary through a 3 cm thick fat layer. The transmission loss through the capillary was about -20 dB, much lower than the -120 dB acoustic attenuation through the fat layer. The overwhelming acoustic attenuation of high-frequency acoustic waves by biological tissue can therefore be avoided by the use of a small footprint capillary acoustic waveguide for remote detection. We finally demonstrate that the capillary can be used as a dual optical-in acoustic-out waveguide, paving the way for the development of minimally invasive optical-resolution photoacoustic endoscopes free of any acoustic or optical elements at their imaging tip

Optical-resolution photoacoustic microscopy by use of a multimode fiber

We demonstrate Optical-Resolution Photoacoustic Microscopy (OR-PAM), where the optical field is focused and scanned using Digital Phase Conjugation (DPC) through a multimode fiber. The focus is scanned across the field of view using digital means, and the acoustic signal induced is collected by a transducer. Optical-resolution photoacoustic images of a knot made by two absorptive wires are obtained and we report on resolution smaller than 1.5{\mu}m across a 201{\mu}m by 201{\mu}m field of view. The use of a multimode optical fiber for the optical excitation part can pave the way for miniature endoscopes that can provide optical-resolution photoacoustic images at large optical depth.Comment: 10 pages, 3 figure

Imagerie photoacoustique : contributions à l'endoscopie photoacoustique à résolution optique et étude expérimentale de la non-linéarité d'origine thermique

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.L’imagerie photoacoustique est une technique hybride qui permet d’obtenir à plusieurs centimètres de profondeur dans les tissus biologiques des images de l’absorption optique avec la résolution des ultrasons. Des agents de contraste peuvent être utilisés pour améliorer le contraste ou imager des récepteurs spécifiques de maladies, mais il existe un compromis entre résolution et profondeur d’imagerie. Cependant, la détection spécifique d’agents de contraste peut nécessiter l’utilisation de l’imagerie multispectrale qui reste un défi à cause de la propagation complexe de la lumière dans les tissus biologiques. Cette thèse propose une nouvelle approche pour la microscopie photoacoustique à résolution optique (OR-PAM) de l’ordre du micron à plusieurs centimètres de profondeur dans les tissus, et étudie expérimentalement la possibilité d’améliorer la détection de nanosphères d’or grâce à la non-linéarité photoacoustique d’origine thermique. Il est d’abord montré que des images OR-PAM peuvent être générées à l’extrémité distale d’une fibre optique multimode grâce à la conjugaison de phase numérique. Il est ensuite montré que des images OR-PAM peuvent être transmises à travers les tissus en les guidant acoustiquement dans un capillaire de silice. Des expériences préliminaires suggèrent que les deux approches précédentes pourraient être combinées pour acquérir des images OR-PAM à travers plusieurs centimètres de tissus via un unique capillaire de silice. Enfin, il est montré que des solutions aqueuses de colorant et de nanosphères d’or peuvent être discriminées grâce à la non-linéarité thermique et la dépendance de l’amplitude photoacoustique avec la fluence ou la température

Development of an acoustic-resolution photoacoustic microscope

International audiencePhotoacoustic imaging is a recent, rapidly growing imaging technique. It has the unique ability to provide images in soft tissues in the optically diffusive regime with both optical absorption contrast and ultrasound resolution. One of the photoacoustic imaging modalities is called acoustic-resolution photoacoustic microscopy. It is aiming at resolution from a few microns to 100 microns over depths up to a centimeter. In this work, a photoacoustic microscope using a mechanically scanned single element focused transducer is described. The following characteristics of our microscope are studied: image contrast, signal-to-noise ratio, resolution and acquisition time, and imaging depth. Images are made at different optical wavelength ranging from 532nm to the near-infrared of the therapeutic window. This set-up is intended to image tumor model on small animals

Minimally Invasive Optical Photoacoustic Endoscopy with a Single Waveguide for Light and Sound

An endoscopic device for photoacoustic imaging, including a multimode optical fiber having a distal end and a proximal end, a light source to provide a light beam to the proximal end of the multimode optical fiber, a transducer to capture acoustic waves that are emitted from the proximal end of the multimode optical fiber, and a processing device to generate a photoacoustic image based on data from the captured acoustic waves captured by the transducer, wherein the distal end of the multimode optical fiber is configured to be inserted into a sample, the sample generating the acoustic waves by a photoacoustic effect

Imaging the dynamics and microstructure of fibrin clot polymerization in cardiac surgical patients using spectrally encoded confocal microscopy

During cardiac surgery with cardiopulmonary bypass (CPB), altered hemostatic balance may disrupt fibrin assembly, predisposing patients to perioperative hemorrhage. We investigated the utility of a novel device termed spectrally-encoded confocal microscopy (SECM) for assessing fibrin clot polymerization following heparin and protamine administration in CPB patients. SECM is a novel, high-speed optical approach to visualize and quantify fibrin clot formation in three dimensions with high spatial resolution (1.0 μm) over a volumetric field-of-view (165 × 4000 × 36 μm). The measurement sensitivity of SECM was first determined using plasma samples from normal subjects spiked with heparin and protamine. Next, SECM was performed in plasma samples from patients on CPB to quantify the extent to which fibrin clot dynamics and microstructure were altered by CPB exposure. In spiked samples, prolonged fibrin time (4.4 ± 1.8 to 49.3 ± 16.8 min, p < 0.001) and diminished fibrin network density (0.079 ± 0.010 to 0.001 ± 0.002 A.U, p < 0.001) with increasing heparin concentration were reported by SECM. Furthermore, fibrin network density was not restored to baseline levels in protamine-treated samples. In CPB patients, SECM reported lower fibrin network density in protaminized samples (0.055 ± 0.01 A.U. [Arbitrary units]) vs baseline values (0.066 ± 0.009 A.U.) (p = 0.03) despite comparable fibrin time (baseline = 6.0 ± 1.3, protamine = 6.4 ± 1.6 min, p = 0.5). In these patients, additional metrics including fibrin heterogeneity, length and straightness were quantified. Note, SECM revealed that following protamine administration with CPB exposure, fibrin clots were more heterogeneous (baseline = 0.11 ± 0.02 A.U, protamine = 0.08 ± 0.01 A.U, p = 0.008) with straighter fibers (baseline = 0.918 ± 0.003A.U, protamine = 0.928 ± 0.0006A.U. p < 0.001). By providing the capability to rapidly visualize and quantify fibrin clot microstructure, SECM could furnish a new approach for assessing clot stability and hemostasis in cardiac surgical patients. © 2021 Wiley Periodicals LLC.12 month embargo; first published: 10 May 2021This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Imaging the dynamics and microstructure of fibrin clot polymerization in cardiac surgical patients using spectrally encoded confocal microscopy

During cardiac surgery with cardiopulmonary bypass (CPB), altered hemostatic balance may disrupt fibrin assembly, predisposing patients to perioperative hemorrhage. We investigated the utility of a novel device termed spectrally-encoded confocal microscopy (SECM) for assessing fibrin clot polymerization following heparin and protamine administration in CPB patients. SECM is a novel, high-speed optical approach to visualize and quantify fibrin clot formation in three dimensions with high spatial resolution (1.0 μm) over a volumetric field-of-view (165 × 4000 × 36 μm). The measurement sensitivity of SECM was first determined using plasma samples from normal subjects spiked with heparin and protamine. Next, SECM was performed in plasma samples from patients on CPB to quantify the extent to which fibrin clot dynamics and microstructure were altered by CPB exposure. In spiked samples, prolonged fibrin time (4.4 ± 1.8 to 49.3 ± 16.8 min, p < 0.001) and diminished fibrin network density (0.079 ± 0.010 to 0.001 ± 0.002 A.U, p < 0.001) with increasing heparin concentration were reported by SECM. Furthermore, fibrin network density was not restored to baseline levels in protamine-treated samples. In CPB patients, SECM reported lower fibrin network density in protaminized samples (0.055 ± 0.01 A.U. [Arbitrary units]) vs baseline values (0.066 ± 0.009 A.U.) (p = 0.03) despite comparable fibrin time (baseline = 6.0 ± 1.3, protamine = 6.4 ± 1.6 min, p = 0.5). In these patients, additional metrics including fibrin heterogeneity, length and straightness were quantified. Note, SECM revealed that following protamine administration with CPB exposure, fibrin clots were more heterogeneous (baseline = 0.11 ± 0.02 A.U, protamine = 0.08 ± 0.01 A.U, p = 0.008) with straighter fibers (baseline = 0.918 ± 0.003A.U, protamine = 0.928 ± 0.0006A.U. p < 0.001). By providing the capability to rapidly visualize and quantify fibrin clot microstructure, SECM could furnish a new approach for assessing clot stability and hemostasis in cardiac surgical patients. © 2021 Wiley Periodicals LLC.12 month embargo; first published: 10 May 2021This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Towards new applications using capillary waveguides

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