Abstract
We previously reported a Doppler optical coherence tomography (DOCT) system design [1] for high-speed imaging with wide velocity dynamic range (up to 28.5 dB when acquiring 8 frames per second), operating at 1.3 m with a coherence length of 13.5 m. Using a developmental biology model (Xenopus laevis), here we test the DOCT system's ability to image cardiac dynamics in an embryo in vivo, with a simple hand-held scanner at 4 ~ 16 frames per second. In particular, we show that high fidelity DOCT movies can be obtained by increasing the reference arm scanning rate (~8 kHz). Utilizing a combination of four display modes (B-mode, color-Doppler, velocity variance, and Doppler spectrum), we show that DOCT can detect changes in velocity distribution during heart cycles, measure the velocity gradient in the embryo, and distinguish blood flow Doppler signal from heart wall motions.
Highlights
Optical coherence tomography (OCT) [2] has been used to study the embryo of Xenopus laevis, in particular its cardiovascular system [3]
With the development of rapid scanning optical delay (RSOD) [5], video rate structural OCT imaging has been applied to Xenopus embryos, at frame rates up to 32 fps with 250 × 125 pixels [6]
We have demonstrated a Doppler optical coherence tomography (DOCT) system capable of imaging the cardiac dynamics of Xenopus laevis with high frame rate and wide velocity dynamic range
Summary
Optical coherence tomography (OCT) [2] has been used to study the embryo (tadpole) of Xenopus laevis (the South African clawed frog), in particular its cardiovascular system [3]. Velocity resolution of ~ 500 μm/s had been achieved under in vivo conditions when imaging the Xenopus embryonic heart; the slow reference arm scanning rate of the early Doppler OCT systems prevented acquisition of color-Doppler movies at real-time frame rates. Using a post-processing technique, blood flow in the heart was visualized at ~ 5 fps, demonstrating the feasibility of color-Doppler OCT imaging of cardiac dynamics. With the development of rapid scanning optical delay (RSOD) [5], video rate structural OCT imaging has been applied to Xenopus embryos, at frame rates up to 32 fps with 250 × 125 pixels [6]. RSOD equipped Doppler OCT demonstrated real-time (8 fps) imaging of the Xenopus embryo heart, with a velocity resolution (expressed in minimum resolvable Doppler shift frequency) of 300 Hz, equivalent to 0.4 mm/s blood flow at 70° Doppler angle [7]. Due to the ease of handling, Xenopus laevis has become a benchmark specimen for demonstrating OCT system performance under in vivo conditions [6,7]
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