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Fluorescence and ultrasound-modulated light correlation (FLUX)

One of the fundamental challenges in wavefront shaping is decorrelation due to the dynamics of the thick tissue. Owing to decorrelation, wavefront solution that focuses through the tissue changes over several milliseconds or even sub-milliseconds. Fast wavefront shaping methods try to speed up the record-playback cycle to catch up with the change. FLUX, on the other hand, use such time-varying signal as the mechanism to image the fluorophores.1

FLUX acquires two kinds of signals, one is the fluorescence light, the other is the ultrasound modulated light. Once the ultrasound focus and the fluorophore coincide with each other, the ultrasound and fluorophore capture the same speckle change. Thus, the two signals present strong correlations. When the ultrasound focus and the fluorophore are at different positions, the fluctuation in the speckle intensity is uncorrelated. Using the correlation as the contrast mechanism, we can image through a living tissue which exhibit short decorrelation time.

flux_concept
Fig. 1, Simplified set-up of FLUX and the results. Ultrasound modulated light is also presented here. Without the correlation, the two fluorophore is not resolved in c.

Reference:

  1. Ruan, H., Liu, Y., Xu, J. et al. Fluorescence imaging through dynamic scattering media with speckle-encoded ultrasound-modulated light correlation. Nature Photonics 14, 511–516 (2020).