Coded Excitation for Crosstalk Suppression in Multi-line Transmit Beamforming: Simulation Study and Experimental Validation

Ling Tong,Alejandra Ortega,Jan D’Hooge,Qiong He,Alessandro Ramalli,Piero Tortoli,Jianwen Luo

doi:10.3390/app9030486

Ling Tong, Alejandra Ortega + Show 5 more

Open Access

https://doi.org/10.3390/app9030486

Copy DOI

Abstract

(1) Background: Multi-line transmit (MLT) beamforming has been proposed for fast cardiac ultrasound imaging. While crosstalk between MLT beams could induce artifacts, a Tukey (α = 0.5)-Tukey (α = 0.5) transmit-receive (TT-) apodization can largely—but not completely—suppress this crosstalk. Coded excitation has been proposed for crosstalk suppression, but only for synthetic aperture imaging and multi-focal imaging on linear/convex arrays. The aim of this study was to investigate its (added) value to suppress crosstalk among simultaneously transmitted multi-directional focused beams on a phased array; (2) Methods: One set of two orthogonal Golay codes, as well as one set of two orthogonal chirps, were applied on a two, four, and 6MTL imaging schemes individually. These coded schemes were investigated without and with TT-apodization by both simulation and experiments; and (3) Results: For a 2MLT scheme, without apodization the crosstalk was removed completely using Golay codes, whereas it was only slightly suppressed by chirps. For coded 4MLT and 6MLT schemes, without apodization crosstalk appeared as that of non-apodized 2MLT and 3MLT schemes. TT-apodization was required to suppress the remaining crosstalk. Furthermore, the coded MLT schemes showed better SNR and penetration compared to that of the non-coded ones. (4) Conclusions: The added value of orthogonal coded excitation on MLT crosstalk suppression remains limited, although it could maintain a better SNR.

Highlights

High frame rate imaging has recently gained increased attention in the field of echocardiography given its potential to reveal new areas of myocardial mechanics and blood flow analysis [1]
Without apodization on transmit and receive, no crosstalk was seen in the image of the Golay-coded 2-multi-line transmit beamforming (MLT) scheme (Figure 6c) within a 55 dB-dynamic range, whereas a slight crosstalk suppression was observed in the image of the chirp-coded 2-MLT scheme (Figure 6d, highest crosstalk at about −46 dB) compared to that of the non-coded 2-MLT scheme (Figure 6b, highest crosstalk at about −40 dB)
For the non-apodized coded 4-MLT and 6-MLT schemes, obvious crosstalk artifacts was observed (Figure 7c–f), though less artifacts were found on the Golay-coded images than on the chirp-coded images in particular in the near field

Summary

Introduction

High frame rate imaging has recently gained increased attention in the field of echocardiography given its potential to reveal new areas of myocardial mechanics and blood flow analysis [1]. The signal-to-noise ratio (SNR), spatial and contrast resolution of the resulting images are degraded due to the lack of focusing. To compensate this limitation, spatial coherent compounding is generally required in which the same region is interrogated several times from different directions and the final image is an average of all acquisitions [5]. The effective gain in frame rate drops by a factor equal to the number of the compounded images.

Objectives

Methods

Results

Conclusion