A method of measuring blood velocity includes obtaining a first velocity image by illuminating a tissue surface with a light source for a first exposure time, obtaining a second velocity image by illuminating the tissue surface with the light source for a second exposure time, computing a first average intensity of a first pixel block at a first predetermined location of the first velocity image and a second average intensity of a second pixel block at a second predetermined location of the second velocity image, identifying mid-range velocities of the first and second pixel blocks, computing an optimal optical coherence parameter based on the mid-range velocity of the first pixel block and the mid-range velocity of the second pixel block, and iteratively re-computing the first velocity image and the second velocity image using the optimal optical coherence parameter.
