Improving the axial resolution in time-reversed ultrasonically encoded (TRUE) optical focusing with dual ultrasonic waves

Qiang Yang; Xiao Xu; Puxiang Lai; Xinzhu Sang; Lihong V. Wang

doi:10.1117/12.2038797

3 March 2014 Improving the axial resolution in time-reversed ultrasonically encoded (TRUE) optical focusing with dual ultrasonic waves

Qiang Yang, Xiao Xu, Puxiang Lai, Xinzhu Sang, Lihong V. Wang

Author Affiliations +

Proceedings Volume 8943, Photons Plus Ultrasound: Imaging and Sensing 2014; 894338 (2014) https://doi.org/10.1117/12.2038797
Event: SPIE BiOS, 2014, San Francisco, California, United States

Abstract

Focusing light inside highly scattering media beyond the ballistic regime is a challenging task in biomedical optical imaging, manipulation, and therapy. This challenge can be overcome by time reversing ultrasonically encoded (TRUE) diffuse light to the ultrasonic focus inside a turbid medium. In TRUE optical focusing, a photorefractive crystal or polymer is used as the phase conjugate mirror for optical time reversal. Accordingly, a relatively long ultrasound burst, whose duration matches the response time of the photorefractive material, is used to encode the diffuse light. With this long ultrasound burst, the resolution of the TRUE focus along the acoustic axis is poor. In this work, we used two transducers, emitting two intersecting ultrasound beams at 3.4 MHz and 3.6 MHz respectively, to modulate the diffuse light within their intersection volume at the beat frequency. We show that light encoded at the beat frequency can be time-reversed and converge to the intersection volume. Experimentally, TRUE focusing with an acoustic axial resolution of ~1.1 mm was demonstrated inside turbid media, agreeing with the theoretical estimation.

Citation Download Citation

Qiang Yang, Xiao Xu, Puxiang Lai, Xinzhu Sang, and Lihong V. Wang "Improving the axial resolution in time-reversed ultrasonically encoded (TRUE) optical focusing with dual ultrasonic waves", Proc. SPIE 8943, Photons Plus Ultrasound: Imaging and Sensing 2014, 894338 (3 March 2014); https://doi.org/10.1117/12.2038797

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KEYWORDS

Ultrasonography

Modulation

Transducers

Ultrasonics

Point spread functions

Acoustics

Light scattering

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