Ultrafast Ultrasound Imaging Using a Resolution and Bandwidth Enhancement Technique

International audienceBackground, Motivation and ObjectiveThe Resolution Enhancement Compression (REC) technique is a coded excitation method developed for improving the axial resolution of ultrasound images. It consists on emitting an amplitude modulated chirp signal that transmits more energy at the frequencies where the ultrasound transducer is less efficient. The focus of this study is to elaborate a new beamforming strategy, which consists of implementing the REC technique in combination with coherent plane wave compounding. The first objective is to get a better performance in term of axial resolution than Conventional Pulse Ultrafast Imaging (CP-UI). The second objective is to demonstrate that in ultrafast imaging, REC offers a larger bandwidth than the one provided by CP-UI.Statement of Contribution/MethodsBoth simulations and experimental setups were performed. Simulations using Field II were conducted with a 128 element array of 8.5 MHz (49% bandwidth at -3 dB). The effective impulse response to be provided by the REC technique was constructed to double the fractional bandwidth (98 % at -3 dB). The linear FM chirp was tapered with a Tukey cosinewindow with a 20% taper and had 3 μs duration. To evaluate the performance of the Wiener filter compression, a phantom containing 2 point targets spaced 7 mm was imaged using the REC technique with coherent plane wave compounding (13 angles, 2° separation). This configuration was compared with a standard image using a single focal depth at 23 mm.To estimate the broadband performance of the REC technique, the axial resolution obtained was compared to the one given by a conventional pulse steered plane wave emission. A similar setup was experimentally used on the research open platform Ula-Op.Results/DiscussionSimulations showed an improvement of 26% of the axial resolution with REC-UI compared to CP-UI. A broader power spectrum was also observed for REC-UI (+69%). The experimental results show that REC is capable of properly compressing the data without amplifying the noise (a). The power spectra of the reflection from the wire at a depth of 23mm is boosted by 21% (at -6dB and -10dB) compared to the conventional approach (c). The axial resolution is also improved for this wire by 16% (i.e., 204 μm for REC-UI and 238 μm for CP-UI) (b). These results suggest that REC and plane waves can be integrated and provide enhanced resolution, boosted bandwidth and faster frame rate than focusedechography