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Proceedings Paper

Passive optical coherence elastography using a time-reversal approach (Conference Presentation)

Paper Abstract

Background and motivation - Conventional Optical Coherence Elastography (OCE) methods consist in launching controlled shear waves in tissues, and measuring their propagation speed using an ultrafast imaging system. However, the use of external shear sources limits transfer to clinical practice, especially for ophthalmic applications. Here, we propose a totally passive OCE method for ocular tissues based on time-reversal of the natural vibrations. Methods - Experiments were first conducted on a tissue-mimicking phantom containing a stiff inclusion. Pulsatile motions were reproduced by stimulating the phantom surface with two piezoelectric actuators excited asynchronously at low frequencies (50-500 Hz). The resulting random displacements were tracked at 190 frames/sec using spectral-domain optical coherence tomography (SD-OCT), with a 10x5µm² resolution over a 3x2mm² field-of-view (lateral x depth). The shear wavefield was numerically refocused (i.e. time-reversed) at each pixel using noise-correlation algorithms. The focal spot size yields the shear wavelength. Results were validated by comparison with shear wave speed measurements obtained from conventional active OCE. In vivo tests were then conducted on anesthetized rats. Results - The stiff inclusion of the phantom was delineated on the wavelength map with a wavelength ratio between the inclusion and the background (1.6) consistent with the speed ratio (1.7). This validates the wavelength measurements. In vivo, natural shear waves were detected in the eye and wavelength maps of the anterior segment showed a clear elastic contrast between the cornea, the sclera and the iris. Conclusion - We validated the time-reversal approach for passive elastography using SD-OCT imaging at low frame-rate. This method could accelerate the clinical transfer of ocular elastography.

Paper Details

Date Published: 24 April 2017
PDF: 1 pages
Proc. SPIE 10067, Optical Elastography and Tissue Biomechanics IV, 1006707 (24 April 2017); doi: 10.1117/12.2251839
Show Author Affiliations
Thu-Mai Nguyen, Institut Langevin (France)
Ali Zorgani, Lab d'Applications thérapeutiques des ultrasons (France)
Mathias Fink, Institut Langevin (France)
Stefan Catheline, Lab d'Applications thérapeutiques des ultrasons (France)
A. Claude Boccara, Institut Langevin (France)

Published in SPIE Proceedings Vol. 10067:
Optical Elastography and Tissue Biomechanics IV
Kirill V. Larin; David D. Sampson, Editor(s)

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