Efficient implementation of a real-time dynamic synthetic aperture beamformer

Synthetic aperture (SA) imaging techniques can provide high resolution over imaging depths, unlike a conventional receive focusing methods (CRDF) that suffered from a considerable degradation in resolution far from a transmit focal depth. However, it is difficult to incorporate SA on modern medical ultrasound imaging systems due to its high computational complexity. In this paper, the efficient implementation of a real-time dynamic SA beamformer where the number of synthetic scanlines is dynamically adjusted based on transmit beam pattern is presented. In the developed dynamic SA imaging system, 128-channel radio-frequency (RF) data are fed into four field programmable gate array (FPGAs, Virtex-5 LX330, Xilinx, USA) chips and 16 synthetic scanlines can be combined. Each FPGA operates at 160 MHz to produce 16 synthetic scanlines in parallel by a time sharing method. The partial synthetic scanline data from each module are sent to an accumulator to combine and stored in an internal buffer. This SA beamforming operation is repeated with RF data acquired from each excitation, and the final 16 synthetic scanline data are transferred to a personal computer (PC) for backend processing and image display. The developed SA beamformer with 16 synthetic beams is implemented by 51% of slice registers, 43% look-up-tables (LUTs), 71% of random access memories (RAMs) and 50% of digital signal processing (DSP) blocks in each FPGA.