In this paper we demonstrate a new algorithm for use in Doppler Optical Coherence Tomography (DOCT) to allow the detection of flow with a peak velocity of over 1.5 m/s. Previous Doppler estimation methods have utilized a transverse Kasai (TK) autocorrelation technique which computes the phase difference between points adjacent in time at the same spatial location, hereon referred to as transversely adjacent points. The maximum detectable TK velocity is low due to the small axial scanning frequency, fa which creates aliasing. To overcome the low sampling rate, we propose using data acquired in the axial direction which has a sampling rate orders of magnitude larger. Taking an autocorrelation in the depth, or axial direction, yields a quantity that can be related to the mean backscattered frequency. We demonstrate that through subtraction of the axial autocorrelation of a moving scatterer from that of a stationary scatterer at the same spatial location, one is able to obtain the Doppler shift with a much higher non-aliased limit. We have defined this method the axial Kasai (AK) technique. Through use of the AK, we demonstrate maximum non-aliased Dopler frequency estimate on a time domain DOCT system to be increased from the TK limit of ±4 kHz to the AK limit of ±1.6 MHz. In contrast to the high detection range of the AK, the TK maintains superior velocity resolution for low flow rates. Through a combined approach with the AK we have demonstrated a dynamic frequency range of over 100 dB with a velocity detection range from 10 μm/s to over 1.5 m/s. The velocity range has been extended to span both microcirculation and cardiac blood velocities.
Morofke, Darren; Kolios, Michael C.; and Yang, Victor XD, "Two-Dimensional Velocity Estimation for Doppler Optical Coherence Tomography" (2007). Physics Publications and Research. Paper 7.