Local time in diffusive media and applications to imaging

TL;DR

This paper explores the concept of local time in diffusive media, providing mathematical expressions and fluctuation analysis to improve imaging techniques that detect local property variations through wave field measurements.

Contribution

It introduces explicit formulas for local time in 1D, 2D, and 3D, and analyzes its fluctuations to enhance inversion algorithms for imaging in diffusive media.

Findings

Expressions for local time in various dimensions.

Analysis of local time fluctuations.

Implications for imaging accuracy and sensitivity.

Abstract

Local time is the measure of how much time a random walk has visited a given position. In multiple scattering media, where waves are diffuse, local time measures the sensitivity of the waves to the local medium's properties. Local variations of absorption, velocity and scattering between two measurements yield variations in the wave field. These variations are proportionnal to the local time of the volume where the change happened and the amplitude of variation. The wave field variations are measured using correlations and can be used as input in a inversion algorithm to produce variation maps. The present article gives the expression of the local time in dimensions one, two and three and an expression of its fluctuations, in order to perform such inversions and estimate their accuracy.