Research Papers: Imaging

Time-reversed ultrasonically encoded optical focusing into tissue-mimicking media with thickness up to 70 mean free paths

[+] Author Affiliations
Honglin Liu, Xiao Xu, Puxiang Lai, Lihong V. Wang

Washington University in St. Louis, Department of Biomedical Engineering, Optical Imaging Laboratory, St. Louis, Missouri 63130

J. Biomed. Opt. 16(8), 086009 (August 01, 2011). doi:10.1117/1.3609004
History: Received March 09, 2011; Revised June 15, 2011; Accepted June 17, 2011; Published August 01, 2011; Online August 01, 2011
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In turbid media such as biological tissue, multiple scattering hinders direct light focusing at depths beyond one transport mean free path. As a solution to this problem, time-reversed ultrasonically encoded (TRUE) optical focusing is proposed based on ultrasonic encoding of diffused laser light and optical time reversal. In TRUE focusing, a laser beam of long coherence length illuminates a turbid medium, where the incident light undergoes multiple scattering and part of it gets ultrasonically encoded within the ultrasonic focal zone. A conjugated wavefront of the ultrasonically encoded light is then generated by a phase conjugate mirror outside the medium, which traces back the trajectories of the ultrasonically encoded diffused light and converges light to the ultrasonic focal zone. Here, we report the latest experimental improvement in TRUE optical focusing that increases its penetration in tissue-mimicking media from a thickness of 3.75 to 7.00 mm. We also demonstrate that the TRUE focus depends on the focal diameter of the ultrasonic transducer.

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© 2011 Society of Photo-Optical Instrumentation Engineers (SPIE)

Citation

Honglin Liu ; Xiao Xu ; Puxiang Lai and Lihong V. Wang
"Time-reversed ultrasonically encoded optical focusing into tissue-mimicking media with thickness up to 70 mean free paths", J. Biomed. Opt. 16(8), 086009 (August 01, 2011). ; http://dx.doi.org/10.1117/1.3609004


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