A New 3D Imaging Technique Integrating Ultrafast Compounding, Hadamard Encoding, and Reconfigurable Fresnel Lensing, demonstrated on a 128-Element, Crossed Electrode Endoscope

Crossed electrode arrays address some the challenges associated with 3D ultrasound imaging because of the significant reduction in the number of elements (2N vs. N²). However, creating a two-way focused 3D image in real-time is difficult with these arrays because azimuth and elevation dimensions cannot be beamformed at the same time. We have developed a new 3D imaging approach that uses the flexibility of bias sensitive substrates to create a high-quality elevation focus on a crossed electrode array. The principle behind this technique is to perform conventional compound imaging with an azimuth set of electrodes, while implementing a bias controllable elevation lens with an elevation set of electrodes. On transmit, the biases are chosen to mimic a Fresnel lens. Then, on receive, Hadamard coding is implemented along the elevation dimension. After decoding, we gain the RF data for each element across the elevation aperture even though there is effectively only one channel in that dimension. A 30MHz, 64x64 element crossed electrode relaxor array was fabricated on a semi-kerfed, electrostrictive substrate and was used to demonstrate the performance of the imaging technique. The -6dB beamwidths were simulated to be 155μm and 170μm in the azimuth and elevation direction respectively and the secondary lobe levels were suppressed below -50dB. Images were generated of a wire phantom to confirm the performance of the elevational focus with good agreement between simulation and experiment.