1. A method for measuring the interframe movement of pixels in a second ultrasound image frame with respect to the pixels in a first ultrasound image frame, said method comprising the steps of: (a) identifying pixels in said first frame that changed in intensity between said first and second frames; (b) dividing said first image into blocks; (c) computing an estimate of the velocity of at least one of said block having pixels that changed therein; (d) for each said block for which said estimate of the velocity was computed, determining if said estimate is valid; (e) computing a velocity value for each block not having a valid estimate by interpolating the valid velocity estimates from at least two other blocks that had valid velocity estimates.