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3D Diverging Waves with 2D Sparse Arrays: A Feasibility Study
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International audience. Background, Motivation and ObjectiveVery high frame rates can be reached both in 2D and 3D ultrasound imaging thanks to diverging waves (DWs) transmission. Up to now 3D ultrafast imaging has been performed controlling full 2D arrays with thousands of active elements which cannot be directly controlled by scanners with limited number of channels. The motivation here is to perform 3D ultrafast imaging with 128, 192 or 256 active elements. We recently addressed a similar issue in focused mode [Roux et al. IEEE UFFC17]: three optimal arrays (opti128, opti192 and opti256) were obtained by reducing the amount of energy out of the main lobe at multiple depths. In this work we experimentally investigate the feasibility of acquiring 3D volumes at high frame rate by transmitting DWs with the opti128, opti192 and opti256 sparse arrays under the hypothesis that these optimal arrays for focused imaging are also the most adequate sparse configurations to produce well resolved and artifactless virtual sources based on time reversal principle.Statement of Contribution/MethodsThe 1024 (32x32) elements of a 3 MHz array made by Vermon were individually driven by four synchronized Verasonics Vantage 256 systems. The systems were programmed to transmit 2.5-cycle sine bursts at 3 MHz. The evaluated image was made by compounding 25 images produced by 5x5 virtual sources located at 25 mm behind the array with span ±15° in both azimuth and elevation. Six arrays were compared: opti128, opti192, opti256, an array whose active elements where randomly selected (rand256) and two references (REF716 and REF1024). The circular dense array REF716 corresponds to the full 32x32 REF1024 array without the corner elements. The comparison criteria were the full width athalf maximum (FWHM) and the contrast to noise ratio (CNR).Results/DiscussionThe results are reported in Table 1. The performance of rand256 in resolution is very close to REF1024 and even better than REF716 whereas the optimized arrays (opti128, opti192 and opti256) yield a resolution about 30 % coarser. However opti256 yields +1dB CNR improvement compared to rand256. The REF716 array is very competitive with REF1024 (+0.3 mm, -0.9 dB) using only 70% of the active elements. As a conclusion, is has been shown that 3D ultrafast imaging can be performed using 2D sparse arrays but potential improvements may be achieved with dedicated optimization e.g. cost function to homogenize DW wavefront.
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