Label-free non-contact imaging of cell nuclei using ultraviolet photoacoustic remote sensing microscopy (Conference Presentation)

Despite advancements in imaging and surgical methodology surgeons continue to face challenges in differentiating suitable margins in tumor resection sites and assessing the extent of cancer proliferation. Presently, histology is the gold standard used for determining margins post-operatively. However, currently no intraoperative tools can analyze entire resection sites. This results in unnecessary repeated surgeries and is especially critical to patient outcome for certain cancers. To address this critical need, we have developed a next-generation microscopy system intended to allow accurate intraoperative virtual histopathology for margin assessment. The modality, named ultraviolet photoacoustic remote sensing microscopy (UV-PARS), takes advantage of the intrinsic optical absorption contrast of DNA at 266 nm and a non-contact PARS technique. This approach measures time-dependent refractive index modulations at their subsurface origin resulting from thermo-elastic excitation from a pulsed excitation source. This enables the possibility of real time non-contact label-free visualization of cell nuclei in vivo. Preliminary results are presented including studies with live cell cultures, excised tissue samples, phantoms, and characterization of system parameters. Lateral-resolution was found to be 0.7 µm with a signal-to-noise ratio of 50 dB achieved in phantoms and 30 dB for HeLa cells. Simultaneously collected confocal reflectance microscopy using 1310 nm light provided cell body morphology. HeLa and PC3 cell cultures were imaged with good agreement to conventional H&E stained images of the same samples.