On the Impact of Microbeamformers in 3-D High Frame Rate Ultrasound Imaging: a Simulation Study

Background and objective: three-dimensional ultrasound imaging is based on two-dimensional (2-D) arrays controlled by application-specific integrated circuits, which implement the so-called microbeamformer (μB) to reduce the channel count. μBs are designed for line-by-line scan sequences based on focused beams (FBs), providing low frame rates. On the other hand, high frame rate (HFR) imaging techniques using defocused beams are increasingly attractive for reconstructing detailed tissue and blood motion information. Although an increasing number of researchers works with μBs integrated into 2-D probes, there is limited literature on the influence of the μB on image quality in HFR imaging applications. Methods: This simulation work evaluates the μB impact on multi-plane HFR transthoracic echocardiography by considering a μB connected to sub-arrays of different sizes (from 2×2 to 8×8 elements). Scan sequences based on the transmission of FBs, focused wide beams (FWB), and planar diverging waves (PDW) were tested. B-mode images were reconstructed and compared to the ideal case (no μB) to assess the image resolution and contrast loss due to the μB. Results: Compared to the ideal case, the μB presence can yield resolution and contrast deterioration up to 17.5% and -26 dB, respectively. Such a deterioration corresponds to the transmission of widest PDW, and can be partially recovered through the synthetic transmit beams technique. Conclusion and significance: A μB designed for FB applications can be used for HFR imaging, although with impaired imaging quality. Guidelines are provided to achieve a suitable trade-off among image quality, μB size, channel number and frame rate.