Simultaneous Azimuth and Fresnel Elevation Compounding: A Fast 3-D Imaging Technique for Crossed-Electrode Arrays

Abstract

We have developed a new, fast, and simple 3-D imaging approach referred to as Simultaneous Azimuth and Fresnel Elevation (SAFE) compounding using a bias-sensitive crossed-electrode array. The principle behind this technique is to perform conventional plane-wave compounding with a back set of electrodes, while implementing a reconfigurable Fresnel elevation lens with an orthogonal set of front electrodes. While a Fresnel lens would usually result in unacceptable secondary lobe levels, these lobes can be suppressed by compounding different Fresnel patterns. The azimuthal and elevational planes can be simultaneously compounded to increase the beam quality with no loss in frame rate. A 10-MHz, $64 \times 64$ element crossed-electrode relaxor array was fabricated on an electrostrictive one-to-three composite substrate to demonstrate the SAFE compounding approach. The electrostrictive composite array has a measured electromechanical coupling coefficient ( $k_{t}$ ) of 0.62 with a bias voltage of 90 V and a measured two-way pulse bandwidth of 60%. The electrical impedance magnitude of array elements on resonance was measured to be $90~\Omega$ with a phase angle of -35°. Radiation patterns were simulated showing a -6-dB beamwidth of $330~\mu \text{m}$ with secondary lobe levels suppressed more than -60 dB in the azimuth dimension, and a -6-dB beamwidth of $450~\mu \text{m}$ with secondary lobe levels suppressed to -50 dB in the elevation dimension after 64 compounds. Experimental radiation patterns were collected and found to be in good agreement with simulations. Experimental 3-D images of wire phantoms were collected using a Verasonics experimental ultrasound system.

Ultrafast Orthogonal Row–Column Electronic Scanning (uFORCES) With Bias-Switchable Top-Orthogonal-to-Bottom Electrode 2-D Arrays

“…This is the largest such TOBE array fabricated to date. The fabrication was conducted with steps similar to those previously described [18] for 64×64 arrays. As shown in Fig.…”

“…Thus, unlike piezoelectric implementations, CMUT-and electrostrictive implementations of TOBE arrays offer bias-sensitivity, which can be used advantageously for novel imaging schemes. These have included Simultaneous Azimuthal and Fresnel Elevational (SAFE) compounding, which exploits Fresnellens-based elevational focusing, introduced by K. Latham et al in [18], [19]. Importantly, each element of such a bias-sensitive TOBE array can be addressed by biasing a row and transmitting or receiving from a column.…”

Anatomic and Functional Imaging Using Row–Column Arrays

“…Chee and Zemp described an advanced modulation scheme in [32], where a combination of individual elements could be acquired simultaneously for the CMUT TOBE array. Other combinations of this scheme were presented in [33] and [34], and results with side lobes below 45 dB were attained. Recent results for a 10 MHz 64 x 64 elements electrostrictive array using Hadamard encoding in transmit for an increased signal-to-noise ratio and synthetic aperture focusing were presented in [35] and for a 30 MHz in [36], demonstrating the good image quality of these arrays and imaging schemes.…”