  Histological images are critical in the diagnosis and treatment of cancers.
Unfortunately, the current method for capturing these microscopy images require
resource intensive tissue preparation that delays diagnosis for many days to a
few weeks. To streamline this process, clinicians are limited to assessing
small macroscopically representative subsets of tissues. Here, we present a
combined photoacoustic remote sensing (PARS) microscope and swept source
optical coherence tomography (SS-OCT) system designed to circumvent these
diagnostic limitations. The proposed multimodal microscope provides label-free
three-dimensional depth resolved virtual histology visualizations, capturing
nuclear and extranuclear tissue morphology directly on thick unprocessed
specimens. The capabilities of the proposed method are demonstrated directly in
unprocessed formalin fixed resected tissues. Here, we present the first images
of nuclear contrast in resected human tissues, and the first 3-dimensional
visualization of subsurface nuclear morphology in resected Rattus tissues,
captured with a non-contact photoacoustic system. Moreover, we present the
first co-registered OCT and PARS images enabling direct histological assessment
of unprocessed tissues. This work represents a vital step towards the
development of a real-time histological imaging modality to circumvent the
limitations of current histopathology techniques.
