  Malignant brain tumors are among the deadliest neoplasms with the lowest
survival rates of any cancer type. In considering surgical tumor resection,
suboptimal extent of resection is linked to poor clinical outcomes and lower
overall survival rates. Currently available tools for intraoperative
histopathological assessment require an average of 20 minutes processing and
are of limited diagnostic quality for guiding surgeries. Consequently, there is
an unaddressed need for a rapid imaging technique to guide maximal resection of
brain tumors. Working towards this goal, presented here is an all optical
non-contact label-free reflection mode photoacoustic remote sensing (PARS)
microscope. By using a tunable excitation laser, PARS takes advantage of the
endogenous optical absorption peaks of DNA and cytoplasm to achieve virtual
contrast analogous to standard hematoxylin and eosin (H and E) staining. In
conjunction, a fast 266 nm excitation is used to generate large grossing scans
and rapidly assess small fields in real-time with hematoxylin-like contrast.
Images obtained using this technique show comparable quality and contrast to
the current standard for histopathological assessment of brain tissues. Using
the proposed method, rapid, high-throughput, histological-like imaging was
achieved in unstained brain tissues, indicating PARS utility for intraoperative
guidance to improve extent of surgical resection.
