A new nonlinear zone-based beamforming method for point-of-care ultrasound: Algorithms and implementation

It is important to reduce the hardware complexity of a dynamic receive beamformer for point-of-care ultrasound imaging systems. In this paper, a new nonlinear zone-based beamforming (ZBF-NLI) method, which can regulate delay errors throughout the imaging depth while reducing the hardware complexity, is proposed. For quantitative evaluation, normalized pixel intensity error (NPE) and mean square error (MSE) were measured from the Field-II simulation and phantom experiments with the allowance error of 0.25 for 16-f0 delay focusing resolution in ZBF-NLI method. Also, the identical number of zones was utilized for both ZBF-LI and ZBF-NLI methods. As a results, the dynamic delays calculated by the ZBF-NLI method shows 0 of MSE, while the ZBF-LI method indicated 0.52. Also, from the 8-bit US images of Field-II simulation and phantom experiment, the 6.16 and 8.39 of normalized pixel intensity error of the ZBF-LI method could be eliminated, respectively, while utilizing the identical number of zones. The ZBF-NLI method was implemented on the low-cost FPGA chip (Spartan 6, Xilinx Inc., CA, USA) of the custom-built portable US imaging system, which indicated that the proposed ZBF-NLI method only requires 9.14% of memory compared to that of the ZBF-LI method (i.e., 16.84 KB vs. 184.32 KB).