Abstract: A pulsed ultrasonic beam is swept over an image field and the backscattered signal is sampled for a multiplicity of timelags to obtain signals from a multiplicity of depths along the beam, the signals forming a two-dimensional set of range cells. A combination of the bandwidth and power of the signal from each range cell is utilized to identify those regions of the image field at which the blood velocity is sufficiently high that Doppler frequency aliasing occurs. These regions are then designated with a single color with strong contrast to the colors employed in the regions wherein the blood velocity is below this limit, so that the regions of high velocity flow are clearly delineated in the image. Where the velocity is sufficiently low that no frequency aliasing occurs, the mean Doppler shift is coded into a continuous distribution of colors for indicating the magnitude of the imaged velocities.