Spatial Coherence of Backscattered Signals in Multi-Line Transmit Ultrasound Imaging and Its Effect on Short-Lag Filtered-Delay Multiply and Sum Beamforming

Giulia Matrone,Alessandro Ramalli

doi:10.3390/app8040486

Giulia Matrone, Alessandro Ramalli

Open Access

https://doi.org/10.3390/app8040486

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Abstract

In Multi-Line Transmission (MLT), high frame-rate ultrasound imaging is achieved by the simultaneous transmission of multiple focused beams along different directions, which unfortunately generates unwanted artifacts in the image due to inter-beam crosstalk. The Filtered-Delay Multiply and Sum (F-DMAS) beamformer, a non-linear spatial-coherence (SC)-based algorithm, was demonstrated to successfully reduce such artifacts, improving the spatial resolution at the same time. In this paper, we aim to provide further insights on the working principle and performance of F-DMAS beamforming in MLT imaging. First, we carry out an analytical study to analyze the behavior and trend of backscattered signals SC in MLT images, when the number of simultaneously transmitted beams and/or their angular spacing change. We then reconsider the F-DMAS algorithm proposing the “short-lag F-DMAS” formulation, in order to limit the maximum lag of signals used for the SC computation on which the beamformer is based. Therefore, we investigate in simulations how the performance of short-lag F-DMAS varies along with the maximum lag in the different MLT configurations considered. Finally, we establish a relation between the obtained results and the signals SC trend.

Highlights

Spatial coherence (SC) of ultrasound backscattered echoes has been the object of numerous works in the ultrasound imaging field
Our group has recently worked towards the joint use of Multi-Line Transmission (MLT) with a new non-linear beamforming algorithm [19], i.e., Filtered-Delay Multiply and Sum (F-DMAS) [8,20,21], and showed how F-DMAS overcomes the main problems that have so far limited the use of MLT in clinical practice. This algorithm basically consists of computing the aperture spatial autocorrelation in reception; the pulse-echo response is heavily jeopardized by MLT imaging [22], the question we address in this work is: does this affect spatial coherence? If so, how?
SC and F-DMAS in MLT imaging, in this work we present the short-lag F-DMAS formulation, which limits the maximum lag M considered in the F-DMAS cross-multiplication stage

Summary

Introduction

Spatial coherence (SC) of ultrasound backscattered echoes has been the object of numerous works in the ultrasound imaging field. The first works date back to the 90s [1,2,3,4,5], when it was proposed to extend to pulse-echo ultrasound the Van Cittert Zernike (VCZ) theorem of statistical optics, which describes the spatial covariance of the wave field generated by an incoherent source [1]. The attention has been focused towards exploiting the concept of spatial coherence for the development of new image reconstruction and beamforming techniques. Coherence (SLSC) imaging [9] The latter is a technique which directly generates an image of the spatial coherence of backscattered echoes evaluated at short lags, while all other methods aim at generating B-mode images, either via a coherence-based weighting or through non-linear.

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