Multiple scattering of ultrasound in weakly inhomogeneous media: application to human soft tissues

TL;DR

This paper introduces a novel method using random matrix theory to distinguish between single and multiple ultrasound scattering in weakly inhomogeneous media, with applications to imaging human tissues.

Contribution

A new technique based on array response matrix properties to separate and analyze single and multiple scattering contributions in ultrasound imaging.

Findings

Single scattering exhibits deterministic coherence along array matrix antidiagonals.

Multiple scattering contribution is significant in breast tissue at 4.3 MHz.

Method allows separate estimation of absorption and scattering losses.

Abstract

Waves scattered by a weakly inhomogeneous random medium contain a predominant single scattering contribution as well as a multiple scattering contribution which is usually neglected, especially for imaging purposes. A method based on random matrix theory is proposed to separate the single and multiple scattering contributions. The experimental set up uses an array of sources/receivers placed in front of the medium. The impulse responses between every couple of transducers are measured and form a matrix. Single-scattering contributions are shown to exhibit a deterministic coherence along the antidiagonals of the array response matrix, whatever the distribution of inhomogeneities. This property is taken advantage of to discriminate single from multiple-scattered waves. This allows one to evaluate the absorption losses and the scattering losses separately, by comparing the multiple scattering intensity with a radiative transfer model. Moreover, the relative contribution of multiple scattering in the backscattered wave can be estimated, which serves as a validity test for the Born approximation. Experimental results are presented with ultrasonic waves in the MHz range, on a synthetic sample (agar-gelatine gel) as well as on breast tissues. Interestingly, the multiple scattering contribution is found to be far from negligible in the breast around 4.3 MHz.