Investigation on synthetic aperture imaging using focused transmit beams for cardiac ultrasonography

In the present study, we examined synthetic aperture imaging using a focused transmit beam. In this investigation, we evaluated the effects of the calculation of the transmit propagation delay time and transmit apodization. The transmit propagation delay time was calculated with the theoretical assumption of the transmitted wave and the propagation delay database created in advance by simulation of the transmitted beam. The results of simulation and phantom experiments showed that the bias error in the estimated motion velocity could be improved from −0.16 to −0.01 mm s⁻¹ and the rms error from ±11.75 to ±8.97 mm s⁻¹ without significant degradation of the spatial resolution at a frame rate about three times higher than that of the conventional method. Furthermore, in the in vivo data analysis, the proposed method depicted temporal changes in myocardial motion velocities within a cardiac cycle without aliasing.