Design of a multiplexing array for 3D cardiac imaging

Volumetric cardiac ultrasound imaging requires 2D matrix array transducers with thousands of elements to allow beam steering and focusing. Controlling all array elements independently is favorable but is expensive and impractical, especially for research purposes. One solution to this is the use of sparse transducers arrays in which not all transducer elements are effectively used. Alternatively, multiplexing (MUX'ing) could offer a solution by grouping various elements in a single electronic channel, reducing the channel count but keeping the array density. However, MUX'ed elements intrinsically share phase and amplitude when transmitting thereby impacting beam forming. Which transducer elements to be grouped into a single electronic channel is thus not obvious. In this paper, a framework to find an optimal MUX configuration for a 3D ultrasound system is presented using two different approaches: The matching algorithm and The virtual array. The two-way beam profiles were simulated as well as for a fully-wired array as a bench mark. To quantify these beam profiles, the side-lobe-to-main-lobe energy ratio (SMER) was computed for a beam focused along the diagonal in the 3D image sequence (focus 60 mm, opening angle of 37.5
^o
). The frameworks have been applied to optimize a 32×32 element phased array transducer combined with a 256-channel front-end using a 1:4 MUX for cardiac imaging. The mean SMER was -33 ± 2 dB for the fully wired array, -28 ± 5 dB for virtual array and -23 ± 3 dB for the matching algorithm array. The proposed MUX'ed probes are all suitable solutions for experimental 3D cardiac ultrasound transducers. Although the virtual array shows the best SMER of the MUX'ed solution, receiving with % of the array could carry image quality problems, while the matched array uses most of the elements on transmit and on receive using all the energy in acquisition, giving more flexibility to the system.