Performance of Ultrasound Vector Velocity Measurement at Great Depths

Ultrasound assessment of blood velocity vectors is usually performed on vessels, like the carotid artery, placed at shallow depths, while only few studies have been presented so far on the investigation of deep vessels. Some vector methods present clear disadvantages at great depth: for example, in multi-beam vector Doppler the inter-beam angle dramatically reduces due to the limited aperture. This problem, in principle, does not affect speckle tracking methods, which could potentially operate even with small transmission apertures. The aim of this work is to investigate the behavior, at different depths, of high frame rate Vector Flow Imaging methods based on the transmission of plane waves. Simulations show that accuracies better than 10% can be obtained for depths shallower than 6 cm but, at higher depths, the performance is significantly affected by the azimuthal broadening of the pressure field.