Overcoming the acoustic diffraction limit in photoacoustic imaging by localization of flowing absorbers

TL;DR

This paper demonstrates that localizing individual flowing absorbers enables super-resolution photoacoustic imaging beyond the acoustic diffraction limit, improving resolution accuracy in scattering media.

Contribution

The study introduces a localization technique inspired by super-resolution imaging to surpass the acoustic diffraction limit in photoacoustic imaging.

Findings

Achieved super-resolved images of microfluidic channels

Localization accuracy better than λ/10

Potential for improved resolution with endogenous and exogenous absorbers

Abstract

The resolution of photoacoustic imaging deep inside scattering media is limited by the acoustic diffraction limit. In this work, taking inspiration from super-resolution imaging techniques developed to beat the optical diffraction limit, we demonstrate that the localization of individual optical absorbers can provide super-resolution photoacoustic imaging well beyond the acoustic diffraction limit. As a proof-of-principle experiment, photoacoustic cross-sectional images of microfluidic channels were obtained with a 15 MHz linear CMUT array while absorbing beads were flown through the channels. The localization of individual absorbers allowed to obtain super-resolved cross-sectional image of the channels, by reconstructing both the channel width and position with an accuracy better than $\lambda/10$. Given the discrete nature of endogenous absorbers such as red blood cells, or that of exogenous particular contrast agents, localization is a promising approach to push the current resolution limits of photoacoustic imaging.