Optimization of synthetic aperture delay-multiply-and-sum reconstruction

Synthetic aperture (SA) acquisition allows for focusing at all points in ultrasound images during reconstruction. Both delay-and-sum (DAS) and delay-multiply-and-sum (DMAS) have been used to reconstruct SA images. An integral part of both algorithms is the aperture size used to define the beam shape with the f-number. Although f-number variation has been studied in DAS reconstruction, there has not been a systematic study on this topic for DMAS reconstruction in SA imaging. In this work, we evaluated the effects of f-number in DMAS reconstruction using an imaging phantom (CIRS 040GSE). We reconstructed DAS and DMAS images of hyperechoic, hypoechoic, and anechoic contrast targets, as well as point targets, while varying the transmit and receive f-numbers between 0 and 7 in 0.2 increments. Generalized contrast-to-noise ratio (gCNR) was measured for contrast targets. The full width at half maximum (FWHM) was evaluated using point targets. When imaging contrast targets, the DAS and DMAS algorithms responded very differently when varying the f-numbers. DMAS produced higher gCNR values with low transmit f-numbers and high receive f-numbers, while DAS produced higher gCNR values with high transmit and receive f-numbers. When evaluating FWHM, the optimal receive f-number was close to 1 for both algorithms.