Doppler Optical Coherence Tomography: Real-Time Optical Sectioning for Microfluidics

Abstract

Doppler optical coherence tomography (DOCT) is an emerging imaging modality demonstrated in 1991 for the first time and is a functional extension of optical coherence tomography (OCT) to including flow measurement. DOCT allows not only high-resolution, non-invasive, cross-sectional imaging but also simultaneous real-time visualization of sample structure and flow. DOCT is often compared to clinical Doppler ultrasound. However, the spatial resolution of clinical Doppler ultrasound is limited to approximately 100 μm due to the relatively long wavelength of acoustic waves. DOCT takes advantage of the short coherence length of broadband light sources in order to achieve cross-sectional images with micrometer (2–10 μm) scale resolution. DOCT is also superior to ultrasound in that DOCT is operated in non-contact-mode. The last four years have witnessed an era of technology revolution in DOCT, introduced by the Fourier-domain technology that shows tremendous advantage over time-domain DOCT. Fourier-domain Doppler optical coherence tomography (FDDOCT) instruments have higher imaging speed and higher system sensitivity which are able to overcome motion artifacts and enhance minimum measurable velocity, respectively. Because of the aforementioned merits, FDDOCT has a broad range of clinical applications including ophthalmology, cardiology, urology, etc with information of tissue microstructure and blood flow. However, FDDOCT has seldom been applied to diagnose microfluidic devices. In this keynote paper, system configuration, principle behind, and applications of FDDOCT for microfluidics will be covered.