Blood flow velocity and wall shear stress (WSS) influence and are influenced
by vascular disease. Their measurement is consequently useful in the laboratory and clinic. Contrast enhanced ultrasound image velocimetry (UIV) can
estimate them accurately but the need to inject contrast agents limits utility. Singular value decomposition and high frame rate imaging may render
contrast agents dispensable. Here we determined whether contrast agent free
UIV can measure flow and WSS. In simulation, accurate measurements were
achieved with a signal-to-noise ratio of 13.5 dB or higher. Signal intensity in
the rabbit aorta increased monotonically with mechanical index and was lowest during stagnant flow and uneven across the vessel. In vivo measurements
with contrast free and contrast enhanced UIV differed by 4.4 % and 1.9 % for
velocity magnitude and angle and by 9.47 % for WSS. Bland–Altman analysis of waveforms showed good agreement between contrast free and contrast enhanced UIV. In five rabbits the root-mean-square error was as low as 0.022
m/s (0.81 %) and 0.11 Pa (1.7 %). This study demonstrates that with an
optimised protocol, UIV can assess flow and WSS without contrast agents.
Unlike contrast enhanced UIV, it could be routinely employed.