Performance Evaluation of a Synthetic Aperture Real-Time Ultrasound System

This paper evaluates the signal-to-noise ratio, the time stability, and the phase difference of the sampling in the experimental ultrasound scanner SARUS: A synthetic aperture, real-time ultrasound system. SARUS has 1024 independent transmit and receive channels and is capable of handling 2D probes for 3D ultrasound imaging. It samples at 12 bits per sample and has a sampling rate of 70 MHz with the possibility of decimating the sampling frequency at the input. SARUS is capable of advanced real-time computations such as synthetic aperture imaging. The system is built using fieldprogrammable gate arrays (FPGAs) making it very flexible and allowing implementation of other real-time ultrasound processing methods in the future. For conventional B-mode imaging, a penetration depth around 7 cm for a 7 MHz transducer is obtained (signal-tonoise ratio of 0 dB), which is comparable to commercial ultrasound scanners. Furthermore, the jitter between successive acquisitions for flow estimation is around 1.41 ps with a standard deviation of 48.3 ps. This has a negligible impact (0.03%) on the flow measurement. Additionally, for the phase of the sampling, it is shown that the small differences between different channels (on average 111 ps for a 70 MHz sampling clock) are deterministic and can therefore be compensated for.