Self-Portrait of the Focusing Process in Speckle: III. Tailoring Complex Spatio-Temporal Focusing Laws To Overcome Reverberations in Reflection Imaging

TL;DR

This paper introduces a method to tailor spatio-temporal focusing laws using matrix imaging and distortion matrix extension to the frequency domain, effectively compensating reverberations in reflection imaging of complex media.

Contribution

It extends the distortion matrix concept to the frequency domain and demonstrates an iterative phase reversal process to improve imaging resolution amidst reverberations.

Findings

Successful imaging of a tissue-mimicking phantom through reverberating media

Enhanced axial and transverse resolution in reflection imaging

Potential applications in transcranial ultrasound imaging

Abstract

This is the third article in a series of three dealing with the exploitation of speckle for imaging purposes. In complex media, a fundamental limit is the multiple scattering phenomenon that completely blurs the imaging process in depth. Matrix imaging can provide a relevant framework for solving this problem. As it proved to be an adequate tool for probing reverberations in speckle [E. Giraudat et al., Part I], we will show how it can be used to tailor complex spatio-temporal focusing laws to monitor the interference between the multiply-reflected paths and the ballistic component of the wave-field. To do so, we extend the distortion matrix concept to the frequency domain. An iterative phase reversal process operated from the space-time Fourier space is then used to compensate for reverberations and optimize both the axial and transverse resolution of the confocal image. Here, we first present an experimental proof-of-concept consisting in imaging a tissue-mimicking phantom through a reverberating plate before outlining the potential and the limits of this strategy for transcranial ultrasound and beyond.