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Proceedings Paper

Dual-wavelength high-speed functional photoacoustic microscopy of mouse brain with a Raman laser at 1-MHz A-line rate (Conference Presentation)

Paper Abstract

Label-free functional photoacoustic microscopy (fPAM) has become a popular technology in small-animal hemodynamic studies. Here we report a stimulated-Raman-scattering-based (SRS) dual-wavelength high-speed fPAM that has achieved volumetric imaging at a 1 MHz A-line rate with capillary-level resolution. Potassium gadolinium tungstate (KGd(WO4)2) crystal is used as a Raman shifter to convert the pump 532 nm picosecond-pulsed laser to the first order Stokes line at 558 nm through the SRS effect with ~40% efficiency and a much narrower line width compared with previous fiber-based SRS PAMs. We also developed a water-immersible micro-electro-mechanical system scanner for scanning a ~4-mm range at a 500 Hz B-scan rate, while maintaining the optic-acoustic confocal alignment. This scanner is assembled entirely from commercially available components, facilitating replication. The detection sensitivity of our fPAM is also improved by employing a high numerical aperture polyvinylidene fluoride ultrasonic transducer, whose acoustic impedance matches better with tissue coupling medium than traditional ceramic transducers. The high sensitivity combined with ~2.4 µm resolution enabled our fPAM to image single red blood cells with a signal-to-noise ratio of ~27 dB. Compared with our previous laser-pulse-width based fPAM, we achieved simultaneous imaging of hemoglobin concentration and oxygenation with a 5-fold increase in imaging speed. Moreover, our system works in a convenient free-space manner compared to previous SRS-based PAMs. We applied it to imaging vasculature and blood oxygen saturation on mouse brains in both resting and stimulated states.

Paper Details

Date Published: 4 March 2019
Proc. SPIE 10878, Photons Plus Ultrasound: Imaging and Sensing 2019, 1087824 (4 March 2019); doi: 10.1117/12.2510658
Show Author Affiliations
Yun He, Washington Univ. in St. Louis (United States)
Caltech (United States)
Junhui Shi, Caltech (United States)
Konstantin I. Maslov, Caltech (United States)
Lihong V. Wang, Caltech (United States)

Published in SPIE Proceedings Vol. 10878:
Photons Plus Ultrasound: Imaging and Sensing 2019
Alexander A. Oraevsky; Lihong V. Wang, Editor(s)

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