Flow measurement without phase information in optical coherence tomography images

Doppler optical coherence tomography (DOCT) is a valuable tool for depth-resolved flow measurements in tissue. However, DOCT is insensitive to flow in the direction normal to the imaging beam and requires knowledge of the phase of the demodulated signal. We present an alternative method of extracting flow information, using speckle of conventional amplitude optical coherence tomography images. Due to the pixel-by-pixel acquisition scheme of conventional OCT, time-varying speckle is manifested as a change in OCT image spatial speckle frequencies. We tested the ability of speckle to provide quantitative flow information using an Intralipid flow phantom. Over a range of velocities, the ratio of high to low OCT image spatial frequencies was shown to bear a linear relation to flow velocity. With two dimensional imaging, flow in a tube and in vivo hamster skin was visualized. This study shows the feasibility of extracting flow from OCT images in all directions without phase information.