On the Use of the Geometric Median in Delay-and-Sum Ultrasonic Array Imaging.

Nicolas Budyn

doi:10.1109/tuffc.2020.2993328

Abstract

Delay-and-sum algorithms are imaging techniques in nondestructive testing, which form images by summing backpropagated signals. Under this approach, a small number of high-intensity signals, such as those from boundary reflections, may create artifacts that degrade the image and hinder defect detection. This article introduces a probabilistic model of the summation, which explains the origin of this effect and proposes to replace the summation in the imaging algorithm by the more statistically robust geometric median. As demonstrated on an experimental inspection using multiview total focusing method and plane wave imaging, this novel technique effectively suppresses some artifacts, at the expense of an increase in the structural noise amplitude and additional diffraction artifacts at the ends of some structural features. As such, the geometric median provides an alternative imaging approach that may improve the performance in some circumstances.

Highlights

I N ULTRASONIC nondestructive testing, delay-and-sum imaging algorithms are a class of established techniques that form an image by synthetically backpropagating the ultrasonic wave field as a postprocessing step, which leads to a constructive interference of the target signal and a destructive interference of the noise [1]
For plane wave imaging (PWI), the ultrasonic data are derived from the full matrix capture (FMC)
If the defect signal is polluted purely by grain noise that is accurately modeled as normally distributed additive noise, the mean is optimal for its suppression

Summary

Introduction

I N ULTRASONIC nondestructive testing, delay-and-sum imaging algorithms are a class of established techniques that form an image by synthetically backpropagating the ultrasonic wave field as a postprocessing step, which leads to a constructive interference of the target signal and a destructive interference of the noise [1]. This is known in medical ultrasound as synthetic aperture imaging [2]. The virtual source aperture technique uses spherical waves diverging from a point behind or in front of the array [7], [8]

Objectives

Results

Conclusion