Frequency-Domain Synthetic Aperture Focusing Techniques for Imaging with Single-Element Focused Transducers

Abstract

Synthetic aperture focusing techniques (SAFT) mathematically synthesize an effective large aperture by scanning a single-element transducer to improve the lateral spatial resolution and extend the depth of field. In this work, two frequency-domain SAFT algorithms are proposed, which are based on the synthetic aperture radar’s wavenumber algorithm. Both algorithms use 2D matched filtering for the image reconstruction. The first algorithm (FD-SAFT-VS) treats the focus of the transducer as a virtual source of finite-sized, where the diffraction effects in the far-field is taken into account in the image reconstruction. The second algorithm (FD-SAFT-DE) uses the simulated point spread function of the imaging system as a filter kernel in the image reconstruction. The performances of the proposed SAFT algorithms were evaluated using a series of simulations for a 25 MHz single-element focused transducer. The image quality was measured in terms of spatial resolution, electronic signal-to-noise ratio (SNR_e), and contrast-to-speckle ratio (CSR) and it was compared with conventional B-mode and time-domain SAFT (TD-SAFT-VPS) imaging methods. The results showed that the FD-SAFT-VS had the smallest spatial resolution and FD-SAFT-DE had the second smallest spatial resolution. In addition, FD-SAFT-DE generally had the higher SNR_e and CSR values compared to other methods. Furthermore, the computation run times of FD-SAFT-VS and FD-SAFT-DE methods were similar and they were 4 to 190 times smaller compared to TD-SAFT-VPS.