Dynamic Ultrasound Beamforming Using Left-to-Right Arithmetic Adders on FPGA

2026-06-30

AI Summary

This work addresses the challenges of implementing conventional parallel adder trees for delay-and-sum (DAS) beamforming on FPGAs—namely, long critical paths, high LUT utilization, and timing closure difficulties, particularly on resource-constrained devices. For the first time, most-significant-digit-first (MSDF) arithmetic is introduced into beamforming adder trees, yielding a novel left-to-right bit-serial architecture that enables runtime dynamic precision adjustment. This approach facilitates a flexible trade-off between image quality and energy consumption with negligible control overhead. Implemented on a Xilinx Zynq XC7Z010 FPGA, the proposed design reduces LUT usage by 2.5× and dynamic power by 23% compared to the best existing implementation, successfully meets timing constraints, and achieves a throughput of 67 frames per second—an 80% improvement.

Abstract

Adder trees are the computational backbone of delay-and-sum (DAS) ultrasound beamforming, where their implementation directly determines the energy, throughput, and area of a real-time imaging pipeline. Conventional parallel adder trees perform full-precision combinational reduction on every sample, leading to wide critical paths, high LUT consumption, and timing failures on small FPGA devices. This paper presents an alternative adder tree architecture based on \emph{left-to-right (LR)} or \emph{most significant digit first (MSDF) arithmetic}. We implement the proposed and conventional adder trees on a Xilinx Zynq XC7Z010 FPGA and evaluate them for DAS beamforming of a 64-channel ultrasound dataset. The proposed design uses 2.5$\times$ fewer LUTs than the smallest conventional tree, successfully meets the timing constraint, and consumes 23\% less dynamic power than the most efficient conventional baseline. A key advantage of the proposed MSDF adder tree is that it can generate high-quality beamformed images without waiting for full-precision completion. This naturally enables dynamic precision at runtime with negligible control overhead, since precision selection is achieved simply by stopping the computation clock after the desired number of cycles. Such quality--energy scalability is fundamentally unavailable in conventional fixed-cycle adder trees. Iso-area replication enables up to 15 parallel instances on the XC7Z010, achieving 67 FPS, which is 80\% higher throughput than the best conventional design.

Problem

• ultrasound beamforming
• adder trees
• FPGA
• delay-and-sum
• real-time imaging

Innovation

• left-to-right adder
• MSDF arithmetic
• dynamic precision
• ultrasound beamforming
• FPGA