Ultrasound Array Signal Compression by Digital Micro-beamforming
Date Issued
2015
Date
2015
Author(s)
Shih, Huei-Hsu
Abstract
Due to the high computational requirements, conventionally real-time ultrasound imaging systems utilize highly parallel hardware architectures, thus resulting in high hardware cost, lack of flexibility on image optimization and algorithm implementation and relatively long system development cycle. On the other hand, a software-based system utilizing highly parallel graphic processing units (GPUs) can alleviate such limitations. However, massive raw data transmission from hardware end to software end, which is up to gigabytes per second, becomes one of the bottlenecks for performing real-time software-based imaging. For example, the popular USB 3.0 can only support data rate up to 0.5GB/s, which cannot support real-time raw data transfer. A feasible solution is to compress raw channel data with low hardware resource requirement on the front end. As previous studies demonstrated, we can get overall compression ratio of 4~5.6 by demodulating the radio frequency data to baseband and applying Walsh transform-based compression methods. However, more data compression is still desired. In this study, we propose the use of micro-beamforming to further compress the amplitude data with following steps: take the first N channels as a group, and delay the channel data based on pre-steering, then sum up the N channels into one single output. The rest of the channels follow the same procedures and the number of output channels can be suppressed by N times. In addition to data compression, we also propose a compensation method to decrease the errors resulting from the micro-beamformed amplitude data. Results show that when a group of 4 channels are used, B-mode images formed by the compressed data have almost the same spatial and contrast resolution as the original ones. Furthermore, the peak signal-to-noise ratio is higher than 50 dB with the application of the compensation method. Moreover, several aperture domain processing algorithms, including phase aberration correction, coherence-based adaptive weighting and color Doppler velocity estimation, were tested with micro-beamforming and reasonable performance is achieved. The proposed method integrates micro-beamforming and the compensation method into the Walsh transform-based architecture, and overall compression ratio was improved by about 27~59%, reaching an overall compression ratio up to 6.3~7.1, which enables real-time data transfer via an USB 3.0 interface. The increased resource utilization is no more than 5% on a Virtex-6 FPGA.
Subjects
array ultrasound imaging
micro-beamforming
pre-steering
compression
Type
thesis
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