2-D Kasai Velocity Estimation for Doppler Optical Coherence Tomography

Optical Coherence Tomography (OCT) is a high-resolution, non-invasive technique to image subsurface tissue and tissue functions. A broadband light source illuminates an object and the reflected photons are processed using an interferometer, demodulated into inphase and quadrature components and then digitized. The captured data contains information about the velocity of the moving scatterers but current Doppler estimation algorithms have a limited velocity detection range. Here we demonstrate Doppler OCT (DOCT) detection of in vivo of blood flow in a rat aorta with over 1 m/s peak velocity through an esophageal DOCT probe using a new processing technique. Previous methods have used a transverse Kasai (TK) autocorrelation estimation to estimate the velocity. By calculating the Kasai autocorrelation with a lag in the depth or axial direction, backscattered frequency information is obtained. Through subtraction with stationary backscattered information, the Doppler shift is obtained by the axial Kasai (AK) technique. Maximum non-aliased Doppler frequency estimation using a time domain DOCT system increased from +/-4 kHz to =+/-1.6 MHz. The TK has better velocity resolution in the low flow rate range and when combined with the AK we demonstrate a dynamic frequency range over 100 dB with a velocity detection range from 10 [micro]m/s to over 1 m/s. This velocity range spans from microcirculation to cardiac blood flow velocities.