Fast label-free photoacoustic-histology (Conference Presentation)

A Frozen section examination is the conventional intraoperative histology method widely used in cancer surgery for tumor margin assessment. However, this method is necessary to perform complicated process including sectioning and staining, which require approximately 15 minutes. Particularly with the ultraviolet (UV) laser (266 nm), photoacoustic microscopy (PAM) showed the capability to visualize cell nuclei without the time consuming procedures by utilizing superior optical contrast of DNA/RNA at this wavelength, which can be a potential alternative of the frozen section. However, previously developed UV-PAM is limited to be applied in intraoperative scenarios because it has suffered from slow imaging speed because of 2D mechanical scanning with linear stepper motors. To overcome this limitation, we developed a fast UV-PAM system based on a 2-axis waterproof microelectromechanical systems (MEMS) scanner with the specially fabricated optical components for UV light. This MEMS scanner enables to scan 3 × 3 mm2 range and acquire 400 × 400 pixels image within 20 seconds. The measured spatial and axial resolutions of the developed system are 2.2 and 39 μm, respectively. Finally, we acquired the histology-like PA image of the mouse kidney with characteristic tubular structures of kidney epithelial cells. In the mouse brain, distinct microstructures such as hippocampus and dentate gyrus were differentiated with the validation of frozen section sample.