| 2-D angle independent blood velocity estimates are typically achieved by combining the Doppler frequency measurements obtained from two US beams with known inter-beam angle. A recently introduced dual-beam vector Doppler method employs one (reference) beam to identify the flow direction, and the other to measure the velocity magnitude. The flow direction is found when the reference beam is set at 90° to the flow, i.e. the corresponding Doppler spectrum is symmetrical around zero frequency. In this paper, we present an approach to automatically track the desired transverse angle. The new method has been implemented in the ULtrasound Advanced Open Platform (ULA-OP), which is connected to a linear array transducer. It is shown that, whichever is the initial beam-flow angle, the extraction of suitable parameters from the Doppler spectrum allows automatically pushing the steering towards the desired transverse orientation. The operator thus takes care only of locating the Doppler sample volume in a suitable position, as in standard duplex measurements, and the local velocity magnitude is automatically estimated. In vitro experiments conducted in both steady and pulsatile flow conditions are reported, showing that the velocity magnitude is accurately measured whichever the initial Doppler angle is over a large range. Successful preliminary application of the angle tracking procedure on the common carotid arteries of 11 volunteers is also discussed. |