Validation of optimal 2D sparse arrays in focused mode: Phantom experiments

There is an increasing interest for sparse 2D arrays as an alternative to full gridded arrays used in commercial systems. This work presents an effective and straightforward solution to perform 3D ultrasound imaging by driving a reduced number of elements of a commercial 2D array. The selection of 128, 192 or 256 elements out of a 32x32 array was based on simulated annealing to produce radiated beam patterns with optimal tradeoff in terms of main lobe width (resolution) and side lobe level (contrast) over a (± 32°) volume. The aim of the present work is to experimentally validate these optimal configurations by performing 3D focused imaging on a phantom. The performance metrics included the lateral resolution and the contrast to noise ratio (CNR), measured on the images obtained by scanning a grayscale phantom. The results show that the optimized 256 elements array performs, as expected, the best among all the compared sparse arrays, presents the same resolution performance as the full array and a -6 dB loss of CNR while using 25% of the active elements.