# Real-Time Volumetric Ultrasound Research Platform with 1024 Parallel Transmit and Receive Channels
## 4 Discussion  
We developed a 1024-channel ultrasound electronic system for research based on four individual 256-channel systems and demonstrated that parallel and synchronous operation of the four 256-channel sub-systems can be achieved using our newly developed synchronization scheme. Having a fully addressable matrix array transducer is optimal for beamforming research in comparison to systems equipped with multiplexers to address all elements with multiple transmit-receive events. While the overall amount of digitized measurement data is not different, such a large channel count system has two advantages. One the one hand, the transmit beam steering benefits from the use of all transducer elements in terms of better waveform generation capabilities and increased acoustic amplitude generated by the full acoustic aperture. On the other hand, the measurement time is reduced by the multiplexing factor used by a system with fewer channels, since the entire 1024-element matrix array data are digitized in a single transmit-receive event, while a 256-channel ultrasound system with a 1:4 multiplexer requires four transmit-receive events, resulting in longer acquisition times. Regarding our target application of clinical volumetric ultrasound research, the shorter recording time is crucial to reduce motion artefacts resulting in blurred volumes; for example, in cardiac imaging and beamforming research caused by incoherent summation of the received echoes. Accordingly, high channel count systems are the better choice for research in volumetric ultrasound. Although other 1024-channel research systems have been published in the past, there are some significant differences. For instance, the 1024-channel system [9] presented by Verasonics needs individual PCs to control each of the four 256-channel sub-system, while our approach is based on a single PC on whose GPUs most of the signal processing and the entire beamforming take place. The ULA-OP synchronized ultrasound system follows a similar principle by using only one PC but uses a different data interface (USB 3.0). In contrast, we chose a PC interface via the PCIe x8 Gen. 2 interfaces, with a data rate of 100 Gbit/s. This enables real-time streaming operation with unlimited measurement, processing and display in the interleaved mode (parallel acquisition and reconstruction). While relying on the established DiPhAS system architecture, we managed to improve the performance of the integrated 1024-channel system, in particular the bandwidth, in comparison to previous DiPhAS generations. On the receive side, the \(-\)3 dB limit is below 300 kHz, compared to 1 MHz for previous generations. On the transmit side, the frequency range could be extended to over 25 MHz, thereby extending the range of possible applications. Thanks to a newly implemented transmit algorithm in the FPGA firmware, it is now possible to generate tri-state transmit signals with a total length of up to 32 us in a 2 ns delay and frequency resolution. Previous generations of DiPhAS could only resolve at 8 ns or were limited to signal lengths of only 4 us, leading to a smaller degree of freedom in the definition of arbitrary signal patterns; for instance, using pulse-width modulation (PWM) schemes. In the first experiments with matrix array transducers, we demonstrated the system's ability to acquire pre-beamformed channel data and successfully implemented a first GPU-based, real-time volumetric imaging modality based on plane wave compounding. The imaging performance was characterized on wire targets with different transducers, highlighting the impact of the number of compounding angles and of the probe geometry. Lateral resolutions (FWHM of the PSF) between 900 and 1800 um were demonstrated and a contrast of 40 to 50 dB was shown on first in-vivo bladder data.