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Published June 26, 2012 | Supplemental Material + Published
Journal Article Open

Deep-tissue focal fluorescence imaging with digitally time-reversed ultrasound-encoded light

Abstract

Fluorescence imaging is one of the most important research tools in biomedical sciences. However, scattering of light severely impedes imaging of thick biological samples beyond the ballistic regime. Here we directly show focusing and high-resolution fluorescence imaging deep inside biological tissues by digitally time-reversing ultrasound-tagged light with high optical gain (~5×10^5). We confirm the presence of a time-reversed optical focus along with a diffuse background—a corollary of partial phase conjugation—and develop an approach for dynamic background cancellation. To illustrate the potential of our method, we image complex fluorescent objects and tumour microtissues at an unprecedented depth of 2.5 mm in biological tissues at a lateral resolution of 36 μm×52 μm and an axial resolution of 657 μm. Our results set the stage for a range of deep-tissue imaging applications in biomedical research and medical diagnostics.

Additional Information

© 2012 The Authors. This work is licensed under a Creative Commons Attribution-NonCommercial-Share Alike 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/3.0/ Received: 21 March 2012, Accepted: 25 May 2012, Published: 26 June 2012. We thank Dr. Ivo M. Vellekoop, Professor Scott E. Fraser, Seung Ah Lee, Mooseok Jang for helpful discussions, and Guoan Zheng as well as Roarke Horstmeyer for comments on the manuscript. This work is supported by NIH 1DP2OD007307-01 and R21 EB012255 as well as DARPA W31P4Q-11-1-0008. B.J. is a recipient of a Sir Henry Wellcome Postdoctoral Fellowship by the Wellcome Trust. Y.M.W. acknowledges support from the National Science Scholarship, awarded by the Agency for Science, Technology and Research, Singapore. Contributions: The idea was conceived by C.A.D. and C.Y. The imaging scheme was developed by Y.M.W., B.J. and C.Y. The experiments were designed and performed by Y.M.W. and B.J. The data analyses were performed by Y.M.W. and B.J. All authors contributed to the preparation of this manuscript. Supplementary Movie 1 (855 kB): Demonstration of optical focus scanning between thick layers of biological tissue. Performing time-reversal and dynamic background cancellation for each location of the focus, we scanned the position of the ultrasound transducer and confirmed that the time-reversed optical focus followed the locations of the ultrasound focus.

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