In-vivo examples of synthetic aperture vector flow imaging

The majority of the commercial ultrasound scanners feature blood flow velocity estimation based on the autocorrelation method, yielding estimates of the axial velocity component only. For studying complex flow patterns like arterial bifurcations or venous confluences, 2-D vector velocity estimates would be needed. Synthetic aperture vector flow imaging could potentially provide this. The purpose of this paper is to test the synthetic aperture vector flow imaging method on challenging in-vivo data. Two synthetic aperture in-vivo data sets are acquired using a commercial linear array transducer and our RASMUS experimental ultrasound scanner. The first data set covers the femoral artery and the confluence of the femoral and saphenous vein of a healthy 26-year-old male volunteer. The second shows the carotid bifurcation of a healthy 32-year-old male volunteer. Both 2 second long data sets are processed, and movies of full vector flow images are generated. This paper presents still frames from different time instances of these movies. The movie from the femoral data tracks the accelerating velocity in the femoral artery during systole and a backwards flow at the end of the systole. A complex flow pattern is seen at the junction of the femoral and saphenous vein. The movie of the carotid bifurcation shows high velocities close to the separating wall between the internal and external carotid, and a vortex tendency at the outermost wall. The volume flow through the femoral artery is extracted from the velocity estimates of the femoral data set by assuming the artery is rotational symmetric. An average volume flow just above 500 ml/min was found for the 26-year-old volunteer. This is in agreement with values found in literature.