Study of phase aberration on coherent plane wave compounding

High frame rate ultrasound imaging systems can implement innovative applications of real-time 3D ultrasound, elastography, and so on. The approach for reaching high frame rate consists of transmitting single plane wave because emission of a single plane wave is enough to form an image. However, due to the lack of transmit focus, the SNR, and contrast are lower than those with line-by-line scanning. Thus, coherent plane wave compounding (CPWC), which can upgrade the imaging quality, has drawn more and more attention recently. Here, we are interested in the effect of phase aberration, caused by inhomogeneity of sound speed, on CPWC imaging. Degradation between image quality with and without phase aberration is estimated and compared with that using line-by-line scanning and single plane wave imaging (PWI), respectively. Near-field phase screen model was used. The correlation length of the simulated phase-aberration profile was 5 mm, and the maximum phase error varied depending on specific simulation conditions. Images of a 3-mm anechoic cyst at 30-mm depth were simulated using Field II. Four beamforming schemes were considered - line-by-line scanning with transmit focusing at the 30-mm depth and dynamic receive focusing (i.e., ideal focusing), PWI, CPWC using 15 angles with 1-degree separation, and CPWC using 31 angles with 1-degree separation. It is found that the effect of phase aberration on PWI is minimum among the four beamforming schemes. The overall wavefront of the transmit plane wave mitigates the phase aberration on transmit. With phase aberration, as the angles of CPWC increase, the degradation in image quality becomes greater, which is similar to the case with ideal focusing, though the image quality can be upgraded by CPWC with more steered angles.