Ultrafast ultrasound imaging is essential for advanced ultrasound imaging
techniques such as ultrasound localization microscopy (ULM) and functional
ultrasound (fUS). Current ultrafast ultrasound imaging is challenged by the
ultrahigh data bandwidth associated with the radio frequency (RF) signal, and
by the latency of the computationally expensive beamforming process. As such,
continuous ultrafast data acquisition and beamforming remain elusive with
existing software beamformers based on CPUs or GPUs. To address these
challenges, the proposed work introduces a novel method of implementing an
ultrafast ultrasound beamformer specifically for ultrafast plane wave imaging
(PWI) on a field programmable gate array (FPGA) by using high-level synthesis.
A parallelized implementation of the beamformer on a single FPGA was proposed
by 1) utilizing a delay compression technique to reduce the delay profile size,
which enables both run-time pre-calculated delay profile loading from external
memory and delay reuse 2) vectorizing channel data fetching which is enabled by
delay reuse, and 3) using fixed summing networks to reduce consumption of logic
resources. Our proposed method presents two unique advantages over current FPGA
beamformers: 1) high scalability that allows fast adaptation to different FPGA
resources and beamforming speed demands by using Xilinx High-Level Synthesis as
the development tool, and 2) allow a compact form factor design by using a
single FPGA to complete the beamforming instead of multiple FPGAs. With the
proposed method, a sustainable average beamforming rate of 4.83 G
samples/second in terms of input raw RF sample was achieved. The resulting
image quality of the proposed beamformer was compared with the software
beamformer on the Verasonics Vantage system for both phantom imaging and in
vivo imaging of a mouse brain