Color Doppler sonography allows the visualization of flow direction and velocity within a user defined area. Apart from assessment of blood vessel patency and direction of flow, it allows quantitation of arterial stenoses and evaluation of both physiologic and pathologic changes in impedance. In certain situations, Doppler US can aid in tissue characterization and estimation of absolute flow volume. In addition, color Doppler imaging can demonstrate flow orientation and improve the identification of turbulence and soft plaque.