Smart optical coherence tomography for ultra-deep imaging through highly scattering media

TL;DR

This paper introduces a matrix-based optical imaging method that significantly extends the depth limit of tissue imaging beyond traditional optical coherence tomography by discriminating ballistic waves and employing iterative time-reversal.

Contribution

It presents a novel matrix approach combined with iterative time-reversal to double the imaging depth in highly scattering media, surpassing current OCT capabilities.

Findings

Extended imaging depth by at least a factor of two

Successful imaging through a strongly scattering layer

Demonstrated detection of a single ballistic photon among 1000 billion

Abstract

Multiple scattering of waves in disordered media is a nightmare whether it be for detection or imaging purposes. The best approach so far to get rid of multiple scattering is optical coherence tomography. It basically combines confocal microscopy and coherence time-gating to discriminate ballistic photons from a predominant multiple scattering background. Nevertheless, the imaging depth range remains limited to 1 mm at best in human soft tissues. Here we propose a matrix approach of optical imaging to push back this fundamental limit. By combining a matrix discrimination of ballistic waves and iterative time-reversal, we show both theoretically and experimentally an extension of the imaging-depth limit by at least a factor two compared to optical coherence tomography. In particular, the reported experiment demonstrates imaging through a strongly scattering layer from which only one reflected photon over 1000 billion is ballistic. This approach opens a new route towards ultra-deep tissue imaging.