Experimental verification of a split-aperture transmit beamforming technique for suppressing grating lobes in large pitch phased arrays

Phased array ultrasound transducers are desirable in some applications where large field-of-view is required from a small aperture. Fabrication of high-frequency phased array transducers is challenging due to the inter-element pitch constraint (∼0.5 λ) to avoid large grating lobe artifacts. Phase coherence imaging (PCI) has been introduced as a method for suppressing grating lobes in large-pitch arrays, however, it is not as effective when the grating lobe echoes have large overlap in the time-domain. In previous work we suggested a technique called split-aperture transmit beamforming to increase the effectiveness of PCI in grating lobe suppression of these arrays and used computer simulation to evaluate its effectiveness. In the present work we report on the experimental verification of the technique using a commercially available high-frequency ultrasound linear array system (Vevo 2100, Visualsonics). We demonstrate that by using only two split-aperture transmit beamforming events along with PCI we can effectively suppress the grating lobes resulting from a 50 MHz, 64-element, 1.26 λ pitch phased array to less than 60 db for a wire-phantom placed at 25 degrees from the center of transducer. We further show that this grating lobe suppression greatly improves the contrast in tissue phantom. Finally, we show that the measured beamformed radiation patterns are consistent with simulations.