Ultrasound phase rotation beamforming on multi-core DSP

Abstract

Phase rotation beamforming (PRBF) is a commonly-used digital receive beamforming technique. However, due to its high computational requirement, it has traditionally been supported by hardwired architectures, e.g., application-specific integrated circuits (ASICs) or more recently field-programmable gate arrays (FPGAs). In this study, we investigated the feasibility of supporting software-based PRBF on a multi-core DSP. To alleviate the high computing requirement, the analog front-end (AFE) chips integrating quadrature demodulation in addition to analog-to-digital conversion were defined and used. With these new AFE chips, only delay alignment and phase rotation need to be performed by DSP, substantially reducing the computational load. We implemented the delay alignment and phase rotation modules on a Texas Instruments C6678 DSP with 8cores. We found it takes 200μs to beamform 2048 samples from 64 channels using 2cores. With 4cores, 20million samples can be beamformed in one second. Therefore, ADC frequencies up to 40MHz with 2:1 decimation in AFE chips or up to 20MHz with no decimation can be supported as long as the ADC-to-DSP I/O requirement can be met. The remaining 4cores can work on back-end processing tasks and applications, e.g., color Doppler or ultrasound elastography. One DSP being able to handle both beamforming and back-end processing could lead to low-power and low-cost ultrasound machines, benefiting ultrasound imaging in general, particularly portable ultrasound machines.