KEYWORDS: Digital signal processing, Phased arrays, Data processing, Image processing, Ultrasonography, Parallel processing, Ultrasonics, Field programmable gate arrays, Filtering (signal processing), Signal processing
We present a software-based ultrasound beamformer to build a fully software-based ultrasound scanner which performs
real-time delay-sum beamforming using fractional delay filters using ADSP-TS201 DPSs (Analog Device Inc.). Receive
dynamic focusing generally requires fast transfer of a large amount of data for inter-channel summation and for delay
control. The DSPs are connected in pipelined network architecture without a glue logic using the DPS's parallel ports,
which allows the connection of unlimited DSPs. Each DSP has a small input FIFO which takes as input the data samples
from each ADC and can take delay values either from a memory (to use pre-calculated delay values) or an external
FPGA (for real-time delay calculation) via its LVDS channel. Two fractional delay beamformer (FDBF) schemes are
implemented on the DSP system. Each scheme is programmed in assembly code optimized for speed; instruction level
parallelism is secured to maximally utilize the four execution units of each DSP, pipeline scheduling is employed to
avoid pipeline stall, and instruction reordering techniques are used to prevent memory contention while preserving the
program semantics. It is found that dynamic focusing is carried out faster when delay filtering is performed prior to interchannel
summation, whereas hardware implementation of the FDBF favors performing delay filtering after interchannel
summation. The frame rate achievable with 16 DSPs is up to 28Hz when the sampling rate is 40MHz, the view depth is
20cm, the number of scanline is 128, and the number of channel is 64.
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