Comparison of parallel beam forming with plane wave imaging for cardiac applications: A simulation study

Parallel beam forming is a commonly used technique to achieve high frame rate for fast cardiac imaging. With 4 multiple line acquisition (4MLA), the frame rate increases by a factor of 4 but a broadened transmit beam is needed to reduce block-like artifacts. As an alternative, plane wave (PW) imaging could be used allowing - for a typical phased array transducer - for 16MLA. However, different transmits then need to be compounded in order to keep the spatial resolution acceptable. As such, an effective gain in frame rate similar to the one of 4MLA can typically be obtained. In this study, the two-way beam profiles of the conventional 4MLA system and the plane wave imaging system were simulated and quantified by averaging the following characteristics over depth (near field: 10 mm - 50 mm, far field: 50 mm - 90 mm) and steering angle (“best cases”: 4 steering angles closest to 0° and “worst cases”: 4 steering angles closest to 45°): - 6dB beam width, side lobes to main lobe ratio (SMER), main lobe centralization (warping), and side lobe asymmetry (skewing). Different windowing functions (i.e. Rectangular, Hanning, Tukey and Hamming) were tested on both of the two imaging methods. Conventional single line acquisition (SLA) with Hanning -Tukey (α=0.3) windowing on transmit and receive respectively were included as a reference. The results showed that 4MLA and PW imaging system seemed competitive while operating at a similar frame rate (i.e. approximately 4-fold of the frame rate of SLA). The 4MLA outperformed PW in the near field, while PW beam profiles showed better characteristics in the far field. In particular, Rectangular apodization on both transmit and receive provided the best beam characteristics for both the 4MLA and PW systems.