In-vivo evaluation of three ultrasound vector velocity techniques with MR angiography

In conventional Doppler ultrasound (US) the blood velocity is only estimated along the US beam direction. The estimate is angle corrected assuming laminar flow parallel to the vessel boundaries. As the flow in the vascular system never is purely laminar, the velocities estimated with conventional Doppler US are always incorrect. Three angle independent vector velocity methods are evaluated in this paper: directional beamforming (DB), synthetic aperture flow imaging (STA) and transverse oscillation (TO). The performances of the three methods were investigated by measuring the stroke volume in the right common carotid artery of eleven healthy volunteers, with magnetic resonance phase contrast angiography (MRA) as reference. The correlation between the three vector velocity methods and MRA were: DB/MRA R=0.84 (pLt0.01); STA/MRA R=0.95 (pLt0.01); TO/MRA R=0.91 (pLt0.01). Bland-Altman plots were additionally constructed and mean differences for the three comparisons were: DB/MRA = 0.17 ml; STA/MRA = 0.07 ml; TO/MRA = 0.24 ml. The three US vector velocity techniques yield quantitative insight in to flow dynamics and can potentially give the clinician a powerful tool in cardiovascular disease assessment.