Absolute Flow Velocity Measurement By Phase-Resolved Doppler Optical Coherence Tomography

Phase-resolved Doppler optical coherence tomography(PR-DOCT)is a functional OCT imaging technique that can provide fast and high-resolution depth-resolved measurement on flow motion in biological tissues.However,a common problem with conventional PR-DOCT is that this technique often measures the flow motion projected onto the OCT beam path.Without knowing the projection angle(Doppler angle)between vessel orientation and the OCT beam path,it is hard to obtain the absolute flow velocity.Moreover,the projection angle is usually missing for in vivo measurement on human blood vessel,which obscures quantitative study on human blood flow.Meanwhile,good phase stability is essential for PR-DOCT to achieve accurate flow velocity measurement.But in swept source OCT that uses k-clocking for the data acquisition,phase-error often occurs due to jitter in the data acquisition electronics.This paper mainly studies the accurate measurement of absolute flow velocity,the main work and contributions are as follows:First,we proposed a home-built swept source OCT.The system mainly include four parts of the system,which is the overall structure design,system control and data acquisition,signal processing and performance evaluation.The software for data acquisition,processing and real-time display was developed on Lab VIEW platform.Next,we proposed a real-time phase-error correction algorithm to guarantee a good accuracy of the absolute velocity measurement.it is often seen that in k-clocked SS-OCT systems phase instability caused by point shifts in the spectrum occurs between consecutive A-lines.This induces phase-errors and consequently deteriorates the accuracy of phase-based flow velocity measurement.To evaluate the performance of this algorithm,a stationary gold mirror was employed as sample for phase analysis.Furthermore,we implemented this algorithm for imaging of human skin.Good-quality skin structure and Doppler image can be observed in real-time after phase-error correction.The results show that the algorithm can effectively correct the jitter-induced phase error in SS-OCT system.Finally,we proposed a novel dual-beam PR-DOCT method to obtain accurate absolute flow velocity,which does not require knowing the projection angle.Two parallel beams are created before entering the imaging lens and subsequently focused into the samples at different angles.The images produced by these two beams are encoded into different depths in single B-scan.This allows for calculating the absolute velocity with the Doppler signals by the two beams.We validated our approach in vitro on an artificial flow phantom on our home-built swept source OCT(SS-OCT).The flow phantom is a capillary with 300?m inner-diameter perfused with milk at constant speed by a syringe pump.Experimental results demonstrated that our method can provide an accurate measurement of absolute flow velocity with independency on the projection angle.