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Abstract-Conventional ultrasound systems acquire ultrasound data sequentially one image line at a time. The architecture of these systems is therefore also sequential in nature and processes most of the data in a sequential pipeline. This often makes it difficult to implement radically different imaging strategies on the platforms and makes the scanners less accessible for research purposes. A system designed for imaging research flexibility is the prime concern. The possibility of sending out arbitrary signals and the storage of data from all transducer elements for 5 to 10 seconds allows clinical evaluation of synthetic aperture and 3D imaging. This paper describes a real-time system specifically designed for research purposes.The system can acquire multichannel data in real-time from multi-element ultrasound transducers, and can perform some real-time processing on the acquired data. The system is capable of performing real-time beamforming for conventional imaging methods using linear, phased, and convex arrays. Image acquisition modes can be intermixed, and this makes it possible to perform initial trials in a clinical environment with new imaging modalities for synthetic aperture imaging, 2D and 3D B-mode, and velocity imaging using advanced coded emissions.The system can be used with 128-element transducers and can excite 128 transducer elements and receive and sample data from 64 channels simultaneously at 40 MHz with 12-bit precision. Two-to-one multiplexing in receive can be used to cover 128 receive channels. Data can be beamformed in real time using the system's 80 signal processing units, or it can be stored directly in RAM. The system has 16 Gbytes RAM and can, thus, store more than 3.4 seconds of multichannel data. It is fully software programmable and its signal processing units can also be reconfigured under software control. The control of the system is done over a 100-Mbits/s Ethernet using C and Matlab. Programs for doing, e.g., B-mode imaging can be written directly in Matlab and executed on the system over the net from any workstation running Matlab. The overall system concept is presented along with its implementation and examples of B-mode and in vivo synthetic aperture flow imaging.

A 3-D super resolution (SR) pipeline based on data from a Row-Column (RC) array is presented. The 3 MHz RC array contains 62 rows and 62 columns with a half wavelength pitch. A Synthetic Aperture (SA) pulse inversion sequence with 32 positive and 32 negative row emissions are used for acquiring volumetric data using the SARUS research ultrasound scanner. Data received on the 62 columns are beamformed on a GPU for a maximum volume rate of 156 Hz, when the pulse repetition frequency is 10 kHz. Simulated and 3-D printed point and flow micro-phantoms are used for investigating the approach. The flow micro-phantom contains a 100 µm radius tube injected with the contrast agent SonoVue. The 3-D processing pipeline uses the volumetric envelope data to find the bubble's positions from their interpolated maximum signal and yields a high resolution in all three coordinates. For the point micro-phantom the standard deviation on the position is (20.7, 19.8 , 9.1) µm (x, y, z). The precision estimated for the flow phantom is below 23 µm in all three coordinates, making it possible to locate structures on the order of a capillary in all three dimensions. The RC imaging sequence's point spread function has a size of 0.58 × 1.05 × 0.31 mm 3 (1.17λ ×2.12λ ×0.63λ), so the possible volume resolution is 28,900 times smaller than for SA RC B-mode imaging.

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Super resolution (SR) imaging is currently conducted using fragile ultrasound contrast agents. This precludes using the full acoustic pressure range, and the distribution of bubbles has to be sparse for them to be isolated for SR imaging. Images have to be acquired over minutes to accumulate enough positions for visualizing the vasculature. A new method for SUper Resolution imaging using the Erythrocytes (SURE) as targets is introduced, which makes it possible to maximize the emitted pressure for good signal-to-noise ratios. The abundant number of erythrocyte targets make acquisition fast, and the SURE images can be acquired in seconds. A Verasonics Vantage 256 scanner was used in combination with a GE L8-18iD linear array probe operated at 10 MHz for a wavelength of 150 µm. A 12 emissions synthetic aperture ultrasound sequence was employed to scan the kidney of a Sprague-Dawley rat for 24 seconds to visualize its vasculature. An ex vivo micro-CT image using the contrast agent Microfil was also acquired at a voxel size of 22.6 µm for validating the SURE images. The SURE image revealed vessels with a size down to 29 µm, five times smaller than the ultrasound wavelength, and the dense grid of vessels in the full kidney was reliably shown for scan times between 1 to 24 seconds. Visually the SURE images revealed the same vasculature as the micro-CT images. SURE images are acquired in seconds rather than minutes without contrast injection for easy clinical use, and they can be measured at full regulatory levels for pressure, intensity, and probe temperature.

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Abstract-The SARUS scanner (Synthetic Aperture Real-time Ultrasound System) for research purposes is described. It can acquire individual channel data for multi-element transducers for a couple of heart beats, and is capable of transmitting any kind of excitation. It houses generous and flexible processing resources that can be reprogrammed and tailored to many kinds of algorithms. The 64 boards in the system house 16 transmit and 16 receive channels each, where data can be stored in 2 GB of RAM and processed using four Virtex 4FX100 and one FX60 FPGAs. The VHDL code can acquire data for 16 channels and perform real-time processing for four channels per board. The receive processing chain consists of three FPGAs. The beamformer FPGA houses 24 focusing units (6 x 4-way) each working in parallel at 220 MHz for parallel four-channel beamforming. The fully parametric focusing unit calculates delays and apodization values in real time in 3D space and can produce 630 million complex samples per second. The processing can, thus, beamform 192 image lines consisting of 1024 complex samples for each emission at a rate of 3200 frames a second yielding full nonrecursive synthetic aperture B-mode imaging at more than 30 high resolution images a second.

Abstract-A compact medical ultrasound beamformer architecture that uses oversampled 1-bit analog-to-digital (A/D) converters is presented. Sparse sample processing is used, as the echo signal for the image lines is reconstructed in 512 equidistant focal points along the line through its in-phase and quadrature components. That information is sufficient for presenting a B-mode image and creating a color flow map. The high sampling rate provides the necessary delay resolution for the focusing. The low channel data width (1-bit) makes it possible to construct a compact beamformer logic. The signal reconstruction is done using finite impulse reponse (FIR) filters, applied on selected bit sequences of the delta-sigma modulator output stream. The approach allows for a multichannel beamformer to fit in a single field programmable gate array (FPGA) device. A 32-channel beamformer is estimated to occupy 50% of the available logic resources in a commercially available midrange FPGA, and to be able to operate at 129 MHz. Simulation of the architecture at 140 MHz provides images with a dynamic range approaching 60 dB for an excitation frequency of 3 MHz.