Imaging with large-aperture arrays with heterogeneous directive elements

We have developed a new imaging algorithm for optimization of the contrast resolution of large-aperture arrays utilizing directive elements with heterogeneous responses. The algorithm employs depth-dependant pre- and post-beamforming filtering to optimize the SNR of the echo data throughout the imaging field. Sub-aperture processing is also employed to maximize the coherence of the echo data, both with respect to tissue aberrations and element heterogeneity. Pre-beamforming and sub-aperture processing leads to significant reduction in imaging artifacts due to reverberations, a significant degradation factor due to the need for water standoff. Images of quality assurance phantoms as well as ex-vivo liver tissue were obtained using our concave (100 mm radius of curvature) 64-element 1 MHz dual-mode array (DMA) and a commercial scanner. The results show that the DMA has a 50 dB field-of-view (FOV) centered at its geometric focus. This FOV extends by 6 cm and 4 cm in the axial and lateral directions, respectively. In addition, the spatial and contrast resolutions of this DMA have been tested using wire targets and speckle cell size calculations and found to be consistent with the transducer bandwidth and aperture size.