High-volume-rate ultrasound 3-D flow imaging with a 2-D spiral array: A simulation study

High-volume-rate ultrasound imaging enables the rendering of complex flow dynamics in 3-D; however, high data rates pose significant hurdles towards real-time implementation. A sparsely populated 256-element 2-D spiral array coupled with unfocused transmissions is a potential solution to these challenges. This work analyzes the impact of sparse element distribution on flow velocity estimation with spherical waves (virtual point source 20mm behind the probe) to extend the field of view beyond the array footprint. Field II was used to simulate straight tube flow (6mm-diameter; 45° tilt; 30cm/s plug-flow; Transmission: 7.5 MHz, 3-cycle) to analyze the velocity estimation bias without the influence of surrounding tissue. It was found that the bias at the inlet, mid-section, and outlet were 20.3%, 8.7%, and 4%, respectively; this variation in bias is due to the change in beam-flow angle from 57.8 deg to 34.9 deg. To evaluate the wide-angle and grating-lobe performance of this configuration, the median Doppler power was compared between the center flow region, flow at the extended regions, and the grating lobe region; the relative power to the center flow region was found to be -12.3dB and -19.5dB for extended and grating-lobe regions respectively. These results suggest that the flow estimation region can be extended beyond the array footprint area but extra considerations on the beam-flow angle must be taken, especially in the case of vector flow.