  Acoustic-resolution optoacoustic microscopy (AR-OAM) retrieves anatomical and
functional contrast from living tissues at depths not reachable with optical
microscopy. The imaging performance of AR-OAM has been advanced with image
reconstruction algorithms providing high lateral resolution ultimately limited
by acoustic diffraction. In this work, we suggest a new model-based framework
efficiently exploiting scanning symmetries for high-resolution reconstruction
of AR-OAM images. The model accurately accounts for the spatial impulse
response and large detection bandwidth of a spherical polyvinylidene difluoride
sensor, which facilitates significantly outperforming synthetic aperture
focusing technique commonly employed in AR-OAM image reconstruction in terms of
image contrast and resolution. Furthermore, reconstructions based on L1-norm
regularization enabled resolving structures indistinguishable with other
methods, which was confirmed by numerical simulations as well as phantom and in
vivo experiments. The achieved performance demonstrates the applicability of
AR-OAM as a super-resolution imaging method capable of breaking through the
limits imposed by acoustic diffraction, thus opening unprecedented capabilities
for the microscopic interrogation of optically opaque tissues in preclinical
and clinical studies.
