Ultrasound Matrix Imaging-Part I: The focused reflection matrix, the F-factor and the role of multiple scattering

TL;DR

This paper introduces a matrix imaging approach for ultrasound that decouples transmitted and received focal spots, enabling detailed aberration quantification and correction through analysis of the focused reflection matrix.

Contribution

It presents a novel time-frequency analysis method for the focused reflection matrix, allowing robust aberration quantification and improved focusing quality assessment in ultrasound imaging.

Findings

Effective separation of single and multiple scattering contributions.

Robust aberration quantification method outperforming coherence factor.

Successful in-vivo validation on human calf ultrasound data.

Abstract

This is the first article in a series of two dealing with a matrix approach for aberration quantification and correction in ultrasound imaging. Advanced synthetic beamforming relies on a double focusing operation at transmission and reception on each point of the medium. Ultrasound matrix imaging (UMI) consists in decoupling the location of these transmitted and received focal spots. The response between those virtual transducers form the so-called focused reflection matrix that actually contains much more information than a confocal ultrasound image. In this paper, a time-frequency analysis of this matrix is performed, which highlights the single and multiple scattering contributions as well as the impact of aberrations in the monochromatic and broadband regimes. Interestingly, this analysis enables the measurement of the incoherent input-output point spread function at any pixel of this image. A fitting process enables the quantification of the single scattering, multiple scattering and noise components in the image. From the single scattering contribution, a focusing criterion is defined, and its evolution used to quantify the amount of aberration throughout the ultrasound image. In contrast to the state-of-the-art coherence factor, this new indicator is robust to multiple scattering and electronic noise, thereby providing a contrasted map of the focusing quality at a much better transverse resolution. After a validation of the proof-of-concept based on time-domain simulations, UMI is applied to the in-vivo study of a human calf. Beyond this specific example, UMI opens a new route for speed-of-sound and scattering quantification in ultrasound imaging.