Spectral Doppler measurements with 2-D sparse arrays

Sparse arrays allow resolving some of the difficulties associated with the use of 2-D probes, such as connectivity problems, cable size, power consumption, cost and computation load for the ultrasound scanner. While sparse arrays have already been used in several imaging tests, their application to Doppler investigations has not been widely reported in the literature. The aim of this work was to experimentally assess at which extent the use of sparse rather than full gridded array impacts on spectral Doppler measurements. Three different sets of element distributions were selected out of a 32x32-element probe: all available elements are active (called REF1024); 256 elements are randomly selected (rand256); 256 elements are “optimally” selected (opti256). Doppler spectra extracted from acquisitions on an agar rotating disk have been evaluated in terms of mean frequency (Fm), -6dB bandwidth (BW), signal to noise ratio (SNR) and signal power (Ps). The results highlight that sparse element distributions do not affect the estimation of Fm while slightly affect the BW. Instead, the SNR is significantly affected, but experimental tests have confirmed that the SNR may be partially recovered by exciting the sparse array probe elements with a higher transmission voltage, to produce the same focal pressure as the full array.