Acousto-optic tomography beyond the acoustic diffraction-limit using speckle decorrelation

Acousto-optic tomography (AOT) enables optical-contrast imaging deep inside scattering samples via localized ultrasound modulation of scattered light. However, the resolution of AOT is inherently limited by the ultrasound focus size, prohibiting microscopic investigations. In the last few years, advances in the field of digital wavefront-shaping have allowed the development of novel approaches for overcoming the acoustic resolution limit of AOT. However, these novel approaches require the execution of thousands of wavefront measurements within the sample speckle decorrelation time, limiting their application to static samples. Here, we show that it is possible to surpass the acoustic resolution limit with a conventional AOT system by exploiting the natural dynamics of speckle decorrelations rather than trying to overcome them. We achieve this by adapting the principles of super-resolution optical fluctuations imaging (SOFI), originally developed for imaging blinking fluorophores, to AOT. We show that naturally fluctuating optical speckle grains can serve as the analogues of blinking fluorophores, enabling super-resolution by statistical analysis of fluctuating acousto-optic signals.