Power Doppler imaging is an ultrasonic technique representing circulating red cells as a colour signal independent of their direction and angle of analysis. This noninvasive technique provides a morphological representation of blood flow within a blood vessel. This in vitro study in pulsed flow enabled three-dimensional reconstruction of blood flow in the bifurcation of the pulmonary artery with automatic shifting of the ultrasound probe and an integral digital transfer of the echographic data. The software for treating the images and for volumic reconstruction of the flow is explained. This technique provides a quantitative method of assessing residual intrastenotic flow with a simple computer system.