  Photoacoustic imaging can achieve high-resolution three-dimensional
visualization of optical absorbers at penetration depths ~ 1 cm in biological
tissues by detecting optically-induced high ultrasound frequencies. Tomographic
acquisition with ultrasound linear arrays offers an easy implementation of
single-side access, parallelized and high-frequency detection, but usually
comes with an image quality impaired by the directionality of the detectors.
Indeed, a simple translation of the array perpendicularly to its median imaging
plane is often used, but results both in a poor resolution in the translation
direction and in strong limited view artifacts. To improve the spatial
resolution and the visibility of complex structures while keeping a planar
detection geometry, we introduce, in this paper, a novel rotate-translate
scanning scheme, and investigate the performance of a scanner implemented at 15
MHz center frequency. The developed system achieved a quasi-isotropic uniform
3D resolution of ~170 um over a cubic volume of side length 8.5 mm, i.e. an
improvement in the resolution in the translation direction by almost one order
of magnitude. Dual wavelength imaging was also demonstrated with ultrafast
wavelength shifting. The validity of our approach was shown in vitro. We
discuss the ability to enable in vivo imaging for preclinical and clinical
studies.
