Two dimensional blood velocity estimation using high frame rate echocardiography with transverse oscillation approach

Blood velocity estimation in the cardiac cavity has been useful to diagnose the heart function. In recent years, the two-dimensional (2D) blood velocity has been estimated by detecting echoes from blood cells obtained by high-frame-rate echocardiography with diverging ultrasound emission and parallel receive beamforming. However, the stability of estimated velocities in the transverse direction (perpendicular to the axial direction) was not enough due to a low transverse frequency of an echo. The transverse frequency can be increased by the receive apodization used in the transverse oscillation (TO) approach. In the present study, the effect of the TO apodization on the accuracy of the blood velocity estimation was examined and the receive apodization was optimized. The errors in 2D velocity vectors estimated by speckle tracking were evaluated by an in-house simulation software which simulates echoes from a scatter-filled tube. The movements of the scatterers were governed by the Hagen-Poiseuille flow with a velocity of 0.4 m/s. In the obtained result, the standard deviations of estimated transverse velocities were 9.5% with the rectangular apodization, 17.0% with the Hanning apodization, and 17.5% with the TO apodization with a distance between peaks in the apodization of 48 elements, respectively, at a flow angle of 45 degree.