Abstract
We developed ultra-high-speed, phase-sensitive, full-field reflection interferometric confocal microscopy (FFICM) for the quantitative characterization of in vivo microscale biological motions and flows. We demonstrated 2D frame rates in excess of 1 kHz and pixel throughput rates up to 125 MHz. These fast FFICM frame rates were enabled by the use of a low spatial coherence, high-power laser source. Specifically, we used a dense vertical cavity surface emitting laser (VCSEL) array that synthesized low spatial coherence light through a large number of narrowband, mutually-incoherent emitters. Off-axis interferometry enabled single-shot acquisition of the complex-valued interferometric signal. We characterized the system performance (~2 μm lateral resolution, ~8 μm axial gating depth) with a well-known target. We also demonstrated the use of this highly parallelized confocal microscopy platform for visualization and quantification of cilia-driven surface flows and cilia beat frequency in an important animal model (Xenopus embryos) with >1 kHz frame rate. Such frame rates are needed to see large changes in local flow velocity over small distance (high shear flow), in this case, local flow around a single ciliated cell. More generally, our results are an important demonstration of low-spatial coherence, high-power lasers in high-performance, quantitative biomedical imaging.
Highlights
Quantifying fluid flow is a major driver of technology development in biomedical imaging
We developed ultra-high-speed, phase-sensitive, full-field reflection interferometric confocal microscopy (FFICM) for the quantitative characterization of in vivo microscale biological motions and flows
We demonstrated 2D frame rates in excess of 1 kHz and pixel throughput rates up to 125 MHz. These fast FFICM frame rates were enabled by the use of a low spatial coherence, high-power laser source
Summary
Quantifying fluid flow is a major driver of technology development in biomedical imaging. In the context of coherent, phase-sensitive imaging, relatively mature Doppler technologies are not able to quantify these transverse flows but rather are limited to flow that is parallel to the optical axis. While numerous coherent imaging-based approaches have been developed recently to quantify microscale transverse flows (see, for example, Refs [8,9,10,11,12].), one limitation of these methods is that the scan priority is parallel to the optical axis. The general concept of spatial coherence gating has been described for some time in both narrowband and broadband interferometric imaging, recent advances in low spatial coherence sources make the concept attractive for high-speed (kHz regime) imaging. Our work is an important demonstration of the potential of low spatial coherence laser sources in massively parallelized cross-sectional optical imaging
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