Fast Focusing of Ultrasound Synthetic Aperture Imaging by Using Virtual Array and Nonuniform Fast Fourier Transform

A fast synthetic aperture (SA) focusing algorithm is proposed in this article to overcome the problem of huge computational complexity in developing high-performance SA ultrasound imaging systems. The proposed method realizes the fast focusing of SA imaging by utilizing a virtual array (VA) technique in combination with nonuniform fast Fourier transform (VA-NUFFT) method. The computational performance of the VA-NUFFT algorithm is evaluated with the computational complexity under acceptable beam errors, compared with the conventional delay-and-sum (DAS) method and the frequency-domain direct method (DM), as well as a multiple NUFFT (M-NUFFT) method. Simulation results reveal that under a beam error level less than -57.4 dB, 25 and 10 reduction ratios of entire real operations can be achieved by the VA-NUFFT at larger SA scan lines of 2048, when compared with the DAS and DM, respectively. In the key SA focusing step, i.e., the "spatial process" step, the computational load of VA-NUFFT is lower than two orders of magnitude of that of the DM. SA imaging of a phantom with four cysts is also simulated and a contrast-to-noise ratio (CNR) criterion is adopted for evaluation of imaging quality. CNR results reflect that SA images of using VA-NUFFT make almost no difference to that of DAS focusing under different signal-to-noise ratios (SNRs).