Conventional ultrasound methods for acquiring color flow images of the blood motion are restricted by a relatively low frame rate and angle dependent velocity estimates. The Plane Wave Excitation (PWE) method has been proposed to solve these limitations. The frame rate can be increased, and the 2-D vector velocity of the blood motion can be estimated. The transmitted pulse is not focused, and a full speckle image of the blood can be acquired for each emission. A 13 bit Barker code is transmitted simultaneously from each transducer element. The 2-D vector velocity of the blood is found using 2-D speckle tracking between segments in consecutive speckle images. The flow patterns of six bifurcations and two veins were investigated in-vivo. It was shown: 1) that a stable vortex in the carotid bulb was present opposed to other examined bifurcations, 2) that retrograde flow was present in the superficial branch of the femoral artery during diastole, 3) that retrograde flow was present in the subclavian artery and antegrade in the common carotid artery during diastole, 4) that vortices were formed in the buckets behind the venous valves in both antegrade and retrograde flow, and 5) that secondary flow was present in various vessels. The in-vivo results have revealed complex flow patterns not previously visualized with ultrasound imaging and indicate a flow complexity in both simple and complex vessel geometries.
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