Fast three-dimensional ultrasound cardiac imaging using multi-transmit beam forming: A simulation study

Current volumetric cardiac ultrasound systems suffer from relatively low spatiotemporal resolution limiting their applicability in clinical practice. We have previously demonstrated in 2D that a proper implementation of a 4 multi-line transmit (4MLT, i.e., 4 simultaneous transmits) system can increase frame rate without compromising spatial resolution or signal-to-noise ratio (SNR) significantly. The aim of the current study was to verify whether our 2D findings could be extrapolated to 3D in order to set up a system that would allow for fast volumetric imaging based on MLT beam forming. In this study, a 64×48-element 2D phased array (2.5 MHz; 50% bandwidth) transmitting 16MLT beams was simulated using a GPU-based implementation of the impulse response method. Based on this transducer, the C-plane two-way beam profiles of a 16MLT system with different MLT transmit patterns were simulated and qualitatively compared to investigate their cross-talk level. In addition, based on our 2D findings, the effect of a (2D) Tukey (α=0.5) apodization was tested on transmit and receive to suppress the cross-talk. The results showed that properly aligning the 16MLT beams along directions close to the diagonal of the 2D transducer aperture resulted in a reduction of cross-talk under about - 50dB level. Similar to our findings in 2D, additional Tukey (α=0.5) apodization could also suppress cross-talk down to - 50dB. These findings show that the proposed 16MLT system may have the potential to generate good volumetric images at 16-fold volume rates without significantly compromising spatial resolution or SNR. In addition, given sufficient parallel beam forming capacity of the system, the proposed 16MLT could be combined with 4 parallel receive lines (4MLA) to increase frame rate by a factor of 64 allowing for dense high quality 90×90 degree volumetric imaging at 30Hz.