# Real-Time Volumetric Ultrasound Research Platform with 1024 Parallel Transmit and Receive Channels
## 3 Results
### Signal Processing and Imaging Pipeline  
The implemented signal processing and image generation pipeline is working in real-time (Figure 13) and the resulting frame rate of volume updates depends on the amount of measurements performed to combine each volume. Using a Biquad-based IIR filter with a lower frequency cutoff of 1 MHz and a Q value of 0.7 already filters out the DC offset of each digitized channel separately, with approx. \(-\)60 dB. In the same way, a high-pass filter is used to remove high-frequency RF noise at frequencies higher than 13 MHz. These  
Figure 12: Array statistics and integration. Array performance with color-coded element-wise signal amplitude (**a**) and the corresponding histogram (**b**). Center frequency and bandwidth statistics are given in (**c**,**d**). Single element response measured against the steel reflector (**e**) and average element transfer function (**f**). Acoustic block prior (**g**) and after housing integration (**h**). filters are applied on the single element channel data before beamforming and again on radio-frequent data after beamforming to eliminate the accumulated offsets. While this IIR filter-based signal conditioning and visualization can be computed without high computational load, the data transfer and beamforming reconstruction are the major bottlenecks regarding the resulting imaging rate. Using a volumetric plane wave compounding technique with 225 tilted plane wave events by using all possible permutations of 15 different transmit angles, in both lateral and elevational dimension (15 \(\times\) 15 angles), the resulting amount of digitized data to be transferred can easily sum up to nearly 3 GByte per single volumetric scan (i.e., 225 events \(\times\) 1024 channels \(\times\) 6000 samples per channel \(\approx\) 2.75 GByte). Due to the data transfer and software timing overhead, we are currently able to use 50 Gbit/s of the maximum PCI express bandwidth of 100 Gbit/s, which results in a pure data transfer repetition rate of approx. 2 volumes per second for this shown setup. In order to increase this volume rate, other beamforming schemes need to be tested in the future (multiple parallel transmit beams, other diverging wave setups with the need for less transmit-receive events) and the actual data transfer rate needs to be optimized to reach the hardware link possibilities. While the data transfer rate is one factor limiting the imaging rate, the beamforming reconstruction does also affect it when a sophisticated receive beam reconstruction technique is used. For a fast preview only the orthogonal slices can be reconstructed in high resolution as those two (bi-plane: XZ, YZ) or three (tri-plane: XZ, YZ, XY) images represent considerably less reconstruction points compared to the full volume reconstruction used for direct volume rendering or volumetric analysis of the data. The GPU-based volumetric receive beamforming reconstruction pipeline computes about 500,000 single samples for any volume/slices dimension with 169 (13 \(\times\) 13) input plane wave angle datasets per second using a NVidia GTX 1080 Ti GPU. This way the preview orthogonal slices can be reconstructed and rendered in real time and high resolution (i.e., 128 beams with 1536 samples each) without any additional overhead in parallel to the next data acquisition. The system imaging performance was characterized using the point-spread function (PSF) analysis with different plane wave compounding experiments for both the Vermon 32 \(\times\) 32 and our custom AMPHORA 26 \(\times\) 39 element matrix array transducer described above. As both transducers do not have a square aperture (Vermon has three inactive rows in-between, resulting in a larger footprint in elevational direction), the PSFs were measured with a wire phantom in two orientations, 0\({}^{\circ}\) and 90\({}^{\circ}\), with the wire being at a depth of 35 mm and orthogonal to the XZ in one and orthogonal to the YZ imaging plane in the other setup.