Cross-correlation-based transverse flow measurements using optical resolution photoacoustic microscopy with a digital micromirror device
A cross-correlation-based method is proposed to quantitatively measure transverse flow velocity using optical resolution photoacoustic (PA) microscopy enhanced with a digital micromirror device (DMD). The DMD is used to alternately deliver two spatially separated laser beams to the target. Through cross-correlation between the slow-time PA profiles measured from the two beams, the speed and direction of transverse flow are simultaneously derived from the magnitude and sign of the time shift, respectively. Transverse flows in the range of 0.50 to 6.84 mm/s 6.84 mm/s are accurately measured using an aqueous suspension of 10-μm-diameter microspheres, and the root-mean-squared measurement accuracy is quantified to be 0.22 mm/s 0.22 mm/s. The flow measurements are independent of the particle size for flows in the velocity range of 0.55 to 6.49 mm/s 6.49 mm/s, which was demonstrated experimentally using three different sizes of microspheres (diameters: 3, 6, and 10 μm). The measured flow velocity follows an expected parabolic distribution along the depth direction perpendicular to the flow. Both maximum and minimum measurable velocities are investigated for varied distances between the two beams and varied total time for one measurement. This technique shows an accuracy of 0.35 mm/s 0.35 mm/s at 0.3-mm depth in scattering chicken breast, making it promising for measuring flow in biological tissue.
Additional Information© 2013 Society of Photo-Optical Instrumentation Engineers. Paper 130377RRR received May 29, 2013; revised manuscript received Aug. 7, 2013; accepted for publication Aug. 9, 2013; published online Sep. 3, 2013. The authors thank Junjie Yao, Amy M. Winkler, Lidai Wang, Chi Zhang, Zhiyuan Shen, and Yonghong He for experimental assistance and helpful discussion, and Professor James Ballard for his close reading of the manuscript. This work was sponsored in part by National Institutes of Health grants DP1 EB016986 (NIH Director's Pioneer Award), R01 EB008085, R01 CA134539, U54 CA136398, R01 EB010049, R01 CA157277, and R01 CA159959. L. V. W. has a financial interest in Microphotoacoustics, Inc. and Endra, Inc., which, however, did not support this work. K. I.M. has a financial interest in Microphotoacoustics, Inc., which, however, did not support this work.
Published - JBO_18_9_096004.pdf