A novel dual beam approach for removing Doppler angle ambiguity

Traditional Doppler methods only measure the axial component of the velocity vector. The lack of information on the beam-to-flow angle creates an ambiguity which can lead to large errors in velocity magnitude estimates. Different triangulation techniques have been so far proposed, which basically perform multiple measurements of the Doppler frequency shift originating from the same region. In this work, an original approach is proposed, in which two ultrasound beams with known relative orientation are directed towards the same vessel, but only one of them is committed to perform a Doppler measurement, while the second ('reference') beam has the specific task of detecting the beam-to-flow angle. The latter goal is achieved by accurately identifying a 90° reference beam-toflow angle through the inspection of the backscattered Doppler signal spectrum. In 'transverse' flow conditions, in fact, such spectrum is expected to be centered on the zero frequency, and even a small deviation from the desired 90° orientation causes a noticeable loss of spectral symmetry. Finally, once the flow direction is known thanks to the reference beam, the velocity magnitude can be directly measured by the other ultrasound beam. Validation of the new method has been performed through experimental tests, of which preliminary results are reported here.