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Proceedings Paper

Motion corrected photoacoustic difference imaging of fluorescent contrast agents
Author(s): Julia Märk; Asja Wagener; Sarah Pönick; Carsten Grötzinger; Edward Zhang; Jan Laufer
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Paper Abstract

In fluorophores, such as exogenous dyes and genetically expressed proteins, the excited state lifetime can be modulated using pump-probe excitation at wavelengths corresponding to the absorption and fluorescence spectra. Simultaneous pump-probe pulses induce stimulated emission (SE) which, in turn, modulates the thermalized energy, and hence the photoacoustic (PA) signal amplitude. For time-delayed pulses, by contrast, SE is suppressed. Since this is not observed in endogenous chromophores, the location of the fluorophore can be determined by subtracting images acquired using simultaneous and time-delayed pump-probe excitation. This simple experimental approach exploits a fluorophorespecific contrast mechanism, and has the potential to enable deep-tissue molecular imaging at fluences below the MPE. In this study, some of the challenges to its in vivo implementation are addressed. First, the PA signal amplitude generated in fluorophores in vivo is often much smaller than that in blood. Second, tissue motion can give rise to artifacts that correspond to endogenous chromophores in the difference image. This would not allow the unambiguous detection of fluorophores. A method to suppress motion artifacts based on fast switching between simultaneous and time-delayed pump-probe excitation was developed. This enables the acquisition of PA signals using the two excitation modes with minimal time delay (20 ms), thus minimizing the effects of tissue motion. The feasibility of this method is demonstrated by visualizing a fluorophore (Atto680) in tissue phantoms, which were moved during the image acquisition to mimic tissue motion.

Paper Details

Date Published: 15 March 2016
PDF: 6 pages
Proc. SPIE 9708, Photons Plus Ultrasound: Imaging and Sensing 2016, 970821 (15 March 2016); doi: 10.1117/12.2207302
Show Author Affiliations
Julia Märk, Technische Univ. Berlin (Germany)
Asja Wagener, Charité Univ. Hospital (Germany)
Sarah Pönick, Charité Univ. Hospital (Germany)
Carsten Grötzinger, Charité Univ. Hospital (Germany)
Edward Zhang, Univ. College London (United Kingdom)
Jan Laufer, Technische Univ. Berlin (Germany)
Charité Univ. Hospital (Germany)

Published in SPIE Proceedings Vol. 9708:
Photons Plus Ultrasound: Imaging and Sensing 2016
Alexander A. Oraevsky; Lihong V. Wang, Editor(s)

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