A comparison between unfocused and focused transmit strategies in cardiac strain imaging

Unfocused ultrasound imaging, particularly coherent compounding with diverging waves, is a commonly employed high-frame rate transmit strategy in cardiac strain imaging. However, the accuracy and precision of diverging wave imaging compared to focused-beam transmit approaches in human subjects is unknown. Three transmit strategies—coherent compounding imaging, composite focused imaging with ECG gating and narrow-beams, and focused imaging with wide-beams—were compared in simulation and in transthoracic imaging of healthy human subjects (n=7). The focused narrow-beam sequence estimated radial end-systolic cumulative strains of a simulated left ventricular deformation with 26% ± 1.5% and 34% ± 1.5% greater accuracy compared with compounding and wide-beam imaging, respectively. Strain estimation precision in transthoracic imaging was then assessed with the Strain Filter on cumulative end-systolic radial strains. Within the strain values where statistically significant differences in precision (E(SNRe|e)) were found between transmit strategies, the narrow-beam sequence estimated radial strain 13% ± 0.71% and 34% ± 8.9% more precisely on average compared to compounding or wide-beam imaging, respectively.