  Spherical matrix arrays arguably represent an advantageous tomographic
detection geometry for non-invasive deep tissue mapping of vascular networks
and oxygenation with volumetric optoacoustic tomography (VOT). Hybridization of
VOT with ultrasound (US) imaging remains difficult with this configuration due
to the relatively large inter-element pitch of spherical arrays. We suggest a
new approach for combining VOT and US contrast-enhanced imaging employing
injection of clinically-approved microbubbles. Power Doppler (PD) and US
localization imaging were enabled with a sparse US acquisition sequence and
model-based inversion based on infimal convolution of total variation (ICTV)
regularization. Experiments in tissue-mimicking phantoms and in vivo in mice
demonstrate the powerful capabilities of the new dual-mode imaging system for
blood velocity mapping and anatomical imaging with enhanced resolution and
contrast.
