Improved plane-wave high frame rate imaging using retrospective transmitfocusing and filter-derived coherence-index weighting

Recently, a wide spectrum of new applications in biomedical ultrasound suchas real time 3D ultrasound and transient elastography has triggered the need ofhigh frame-rate imaging. One of the methods to achieve high frame-rate imagingis to use plane wave excitation (PWE) with which a single insonification issufficient to form an image. However, due to the lack of transmit focusing, thesignal-to-noise-ratio (SNR), contrast, and spatial resolution of the resultantimages are lower compared with a conventional focused transmission. To solvethis problem, we propose a filter-based retrospective focusing techniquecombined with filter-derived coherence-index weighting (FRFFCI weighting) forhigh frame-rate imaging with PWE. A 2-D filter is designed and applied tobeamformed baseband data to retrieve transmit focusing. Then a filter-derivedcoherence index (FCI) at each imaging point is used as a weighting factor tofurther improve the filter-retrieved focusing quality. Here FCI is a coherencemeasure of the filtered signal samples in the sliding filter kernel, Due to thesidelobe-suppression nature of the designed 2-D filter, FCIs are low atsidelobes; thus FCI weighting can further suppress the sidelobes in the filteredsignal samples. Simulation results demonstrated that our proposed FRFFCIweighting technique can enhance the image quality of high frame-rate imagingwith single PWE reducing the sidelobes, and improving the SNR and spatialresolution while being capable of retaining the high frame rate. Since it isapplied over high frame-rate imaging with single PWE, FRFFCI weighting performedafter beamforming is inherently insusceptible to motion artifacts. In addition,coded excitation techniques can be integrated into our technique to furtherimprove SNR.