Next-generation ultrasound research scanners design

In a few years, ultrasound research platforms, also known as open scanners, have become a unique tool for the experimental activities of ultrasound labs. A number of advanced research platforms, designed according either to the software-or to the hardware-based approach, is now available. In this paper, the criteria followed in the recent development of ULA-OP 256, a 256-channel research scanner, are reported, and some illustrative scanner applications are presented. Differently from open systems that adopt a software approach based on the acquisition of raw data through high-speed serial links followed by elaboration performed by GPUs, ULA-OP 256 was designed to permit continuous real-time processing of data before their transmission to a host CPU. The new open scanner was programmed to satisfy the requirements of different real-time applications. The implementation of an efficient FPGA-based parallel beamformer allows, in association with the transmission of plane waves, to continuously produce (compounded) B-Mode images at high frame rates (more than 5 kHz). The capability of transmitting arbitrary sequences and waveforms was exploited to implement, in real-time, the multi-line transmit modes so far used off-line in cardiac imaging. The processing power of onboard DSPs is exploited in vector Doppler applications in which the velocity profiles along eight parallel lines are detected at PRF higher than 10 kHz. Novel beamforming methods like the Filtered-Delay Multiply and Sum (FDMAS) were first tested through the acquisition of raw radiofrequency data, and then implemented in real-time. Future directions for possible further improvement of research scanners performance are also discussed.